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Self-diagnosis
Evaluating measured value blocks, engine codes AHU, 1Z
Display group 000 at idling speed (engine warm, coolant temperature not below 80 °C)
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Display group 000 (decimal value displayed)
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▪ Engine running at idling speed
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Read measured value block 0
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◂ Indicated on display
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x
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x
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x
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x
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x
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x
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x
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x
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x
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x
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1
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2
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3
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4
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5
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6
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7
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8
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9
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10
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◂ Display zones
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Specification
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Corresponds to
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Air mass1)
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69...111
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230...370 mg/H
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Fuel temperature
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91...201
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20...80°C
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Intake manifold temperature
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182...50
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10...100°C
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Coolant temperature
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80...35
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80...110°C
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Atmospheric pressure
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Not relevant
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---
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Intake manifold pressure
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Not relevant
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---
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Injected quantity
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11...45
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2.2...9 mg/H
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Accelerator pedal position
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0
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0 %
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Commencement of injection
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0...88
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3°ATDC...4°BTDC
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Engine speed
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41...45
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861...945 rpm
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1) The measured values require the exhaust gas recirculation (EGR) to be switched on. The EGR is switched off after approx. 10 minutes at idling speed, therefore give burst on throttle or restart engine.
Display group 001 at idling speed (engine warm, coolant temperature not below 80 °C)
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Display group 001 -Injected quantity-
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Read measured value block 1
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⇒
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◂ Indicated on display
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xxxx rpm
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xx.x mg/H
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x.xx V
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xxx.x °C
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1
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2
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3
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4
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◂ Display zones
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Specification
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Evaluation
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Coolant temperature
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80...110 °C
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---
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Modulating piston movement sender voltage
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1.25...1.70 V
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Injected quantity
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2.2...9 mg/H
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=> Page 01-62
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Engine speed
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861...945 rpm
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---
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Evaluation: Injected quantity display
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V.A.G 1551 display
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Possible fault cause
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Fault elimination
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Below 2.2 mg/H
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- Injection pump too rich
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- Renew injection pump => Page 23-19
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Above 9 mg/H
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- Engine too cold
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- Run engine at increased speed to warm up and repeat check
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- Injection pump too lean
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- Renew injection pump => Page 23-19
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Evaluation: Modulating piston movement sender voltage display
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V.A.G 1551 display
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Possible fault cause
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Fault elimination
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Below 1.25 V
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- Injection pump too rich
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- Renew injection pump => Page 23-19
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Above 1.70 V
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- Engine too cold
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- Run engine at increased speed to warm up and repeat test
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- Injection pump too lean
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- Renew injection pump => Page 23-19
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Display group 002 at idling speed (engine warm, coolant temperature not below 80 °C)
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Display group 002 -idling speed-
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Read measured value block 2
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⇒
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◂ Indicated on display
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xxxx rpm
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xxx.x %
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xxx
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xxx.x °C
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1
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2
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3
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4
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◂ Display zones
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Specification
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Evaluation
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Coolant temperature
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80...110 °C
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---
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Operating condition
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010
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=> Page 01-64
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Accelerator pedal position
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0 %
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=> Page 01-64
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Engine speed
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861...945 rpm
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---
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Evaluation: Accelerator pedal position display
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V.A.G 1551 display
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Possible fault cause
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Fault elimination
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1...100 %
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- Accelerator position sender -G79 incorrectly set or defective
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- Check G-79 and adjust if necessary
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- Wiring open circuit to G79
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Evaluation: Operating condition display
Significance of figures in 3-digit number block for engine operating condition:
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Significance when display = 1
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x
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x
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x
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Engine operating condition
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1
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Air conditioner compressor switched on
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1
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Idling switch closed
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1
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Increased idling speed because air conditioner is switched on
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Display group 003 at idling speed (engine warm, coolant temperature not below 80 °C)
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Display group 003 -Exhaust gas recirculation-
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Read measured value block 3
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⇒
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◂ Indicated on display
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xxxx rpm
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xxx mg/H
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xxx mg/H
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xxx %
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1
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2
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3
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4
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◂ Display zones
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Specification
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Evaluation
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Duty cycle from exhaust gas recirculation valve
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10...90 %
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---
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Air mass drawn in (actual)1)
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230...370 mg/H
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=> Page 01-66
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Air mass drawn in (specified)
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230...420 mg/H
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=> Page 01-65
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Engine speed
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861...945 rpm
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---
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1) The measured values require the exhaust gas recirculation (EGR) to be switched on. The EGR is switched off after approx. 10 minutes at idling speed, therefore give burst on throttle or restart engine.
Evaluation: Air mass drawn in (specified) display
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V.A.G 1551 display
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Possible fault cause
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Fault elimination
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Above 420 mg/H
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- Engine too cold
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- Run engine at increased speed to warm up and repeat check.
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Evaluation: Air mass drawn in (actual) display
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V.A.G 1551 display
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Possible fault cause
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Fault elimination
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Below 230 mg/H
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- Excessive exhaust gas recirculation
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- Checking exhaust gas recirculation
=> Page 23-89
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- Unmetered air
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- Check intake air system for leaks.
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Above 370 mg/H
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- Engine too cold
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- Run engine at increased speed to warm up and repeat check.
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- Insufficient exhaust gas recirculation
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- Engine running at idling speed for 10 mins., give burst on throttle.
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- Air mass meter -G70 defective
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- Check exhaust gas recirculation and air mass meter function => Page 23-89
If a fault is present the measured value block indicates a constant air mass value of approx. 425 mg/H over the complete rpm and load range.
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Display group 004 at idling speed (engine warm, coolant temperature not below 80 °C)
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Display group 004 -Commencement of injection-
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Read measured value block 4
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⇒
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◂ Indicated on display
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xxxx rpm
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xx.x °
B/ATDC
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xx.x °
B/ATDC
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xxx %
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1
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2
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3
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4
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◂ Display zones
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Specification
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Evaluation
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Commencement of injection valve duty cycle
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2...10 %1)
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Commencement of injection (actual)
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3°ATDC...4°BTDC
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=> Page 01-68
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Commencement of injection (specified)
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3°ATDC...4°BTDC
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=> Page 01-68
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Engine speed
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861...945 rpm
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---
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1) The duty cycle can be up to 50 % on new vehicles or vehicles with a new engine.
Evaluation: Commencement of injection (specified) display
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V.A.G 1551 display
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Possible fault cause
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Fault elimination
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Earlier than 4°BTDC
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- Engine too cold
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- Run engine at increased speed to warm up and repeat check.
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Evaluation: Commencement of injection display (actual)
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V.A.G 1551 display
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Possible fault cause
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Fault elimination
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Earlier than 4°BTDC
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- Engine too cold
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- Run engine at increased speed to warm up and repeat check.
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- Injection pump set too "advanced"
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- Check and adjust commencement of injection dynamically => Page 23-25
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- Commencement of injection valve -N108 defective
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- Check -N108 => Page 01-51, final control diagnosis
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Later than 3°ATDC
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- Injection pump set extremely "retarded"
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- Check and adjust commencement of injection dynamically => Page 23-25
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- Injection adjustment blocked
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- Check -N108 => Page 01-51, final control diagnosis
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- Commencement of injection valve -N108 defective
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Evaluation: Commencement of injection valve duty cycle
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V.A.G 1551 display
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Possible fault cause
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Fault elimination
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Earlier than 10 %1)
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- Injection pump set extremely "retarded"
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- Check and adjust commencement of injection dynamically => Page 23-25
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Display group 005
The values displayed are not relevant for fault finding within the service department.
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Display group 005 -Starting conditions-
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Read measured value block 5
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⇒
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◂ Indicated on display
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xxxx rpm
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xx.x mg/H
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xx.x °
B/ATDC
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xxx.x °C
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1
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2
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3
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4
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◂ Display zones
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Specification
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Evaluation
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Coolant temperature
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---
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---
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Commencement of injection (actual)
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---
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---
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Starting quantity
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---
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---
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Engine speed
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---
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---
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Display group 006 with ignition switched on
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Display group 006 -Switch positions-
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Read measured value block 6
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⇒
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◂ Indicated on display
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xxx km/h
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xxx
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xxxxxx
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xxx
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1
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2
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3
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4
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◂ Display zones
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Specification
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Evaluation
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Cruise control system1)
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---
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---
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Cruise control system
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=> Page 01-71
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Brake pedal monitor
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=> Page 01-71
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Speed
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---
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---
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1) 0 = Cruise control system free
1 = Cruise control system off
2 = Accelerating
4 = Delay
8 = Speed accepted again
16 = Brake pedal depressed
32 = Hold speed
64 = Not relevant
128 = Not relevant
255 = Cruise control system blocked
Evaluation: Brake pedal monitor display
Significance of figures in 3-digit number block for brake pedal monitor:
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Significance when display = 1
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x
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x
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x
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Brake pedal monitor
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1
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Brake light switch -F- closed
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1
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Brake pedal switch -F-47- open
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1
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Clutch pedal switch -F36- open
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Evaluation: Cruise control system display
Significance of figures in 6-digit number block for cruise control system:
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"1" signifies:
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x
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x
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x
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x
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x
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x
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Cruise control system
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1
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Cruise control system "switched off" (button in OFF position)1)
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1
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1
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Cruise control system switched on
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1
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1
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1
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SET-button operated
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1
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1
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1
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Resuming set speed
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1) If the cruise control system switch is in "OFF" position, then "000000" is displayed in number block 3.
Display group 007 with ignition switched on (engine cold and not running)
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Display group 007 -Temperatures-
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Read measured value block 7
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⇒
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◂ Indicated on display
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xxx.x °C
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xxx.x °C
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xxx.x °C
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1
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2
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3
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4
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◂ Display zones
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Specification
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Evaluation
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Coolant temperature
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Approx. ambient temperature1)
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=> Page 01-73
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Intake manifold temperature
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Approx. ambient temperature1)
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=> Page 01-73
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No display
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Fuel temperature
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Approx. ambient temperature1)
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=> Page 01-73
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1) Details of temperature specifications are not possible. When the engine is cold the fuel, intake air and coolant temperatures must equate approximately to ambient temperature. If a temperature deviates noticeably then the relevant sender must be checked.
Evaluation: Fuel temperature display
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V.A.G 1551 display
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Possible fault cause
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Fault elimination
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- 5.6 °C
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- Short circuit or fuel temperature sender
- -G81 defective
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- Check G81 => Page 23-56
If a fault is present the measured value block shows a fuel temperature of -5.6 °C
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Evaluation: Intake manifold temperature display
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V.A.G 1551 display
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Possible fault cause
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Fault elimination
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Approx. 19 °C
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- Intake manifold temperature sender -G72 defective
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- Check G72 => Page 23-51
If a fault is present the measured value block shows a constant intake manifold temperature of approx.19°C an
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Evaluation: Coolant temperature display
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V.A.G 1551 display
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Possible fault cause
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Fault elimination
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Large deviation from ambient temperature
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- Short circuit or coolant temperature sender -G62 defective
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- Check G62 => Page 23-40
If a fault is present the fuel temperature is displayed alternatively
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Display group 009
The values displayed are not relevant for fault finding within the service department.
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Display group 009 -Injected quantity limitation-
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Read measured value block 9
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⇒
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◂ Indicated on display
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xxxx rpm
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xx.x mg/H
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xx.x mg/H
|
x.xx V
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1
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2
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3
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4
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◂ Display zones
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Specification
|
Evaluation
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Modulating piston movement sender voltage
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---
|
---
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Injected quantity limitation from automatic gearbox during gear change
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---
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---
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Injected quantity (cruise control system active)
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---
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---
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Engine speed
|
---
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---
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Display group 012
The values displayed are not relevant for fault finding within the service department.
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Display group 012 -Glow plug system-
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Read measured value block 12
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⇒
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◂ Indicated on display
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xxxx
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xx.xx sek.
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xx.x V
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xxx.x °C
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1
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2
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3
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4
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◂ Display zones
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Specification
|
Evaluation
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Coolant temperature
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---
|
---
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Supply voltage from control unit
|
---
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---
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Pre-glow period
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---
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---
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Not relevant
|
---
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---
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Display group 013 at idling speed (engine warm, coolant temperature not below 80 °C)
|
Display group 014 -Smooth idling speed control-
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Read measured value block 13
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⇒
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◂ Indicated on display
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x.xx mg/H
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x.xx mg/H
|
x.xx mg/H
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1
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2
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3
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4
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◂ Display zones
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Specification
|
Evaluation
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No display
|
|
---
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Different quantity injected Cyl. 1 and Cyl. 3
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- 2.0...+ 2.0 mg/H
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=> Page 01-77
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Different quantity injected Cyl. 2 and Cyl. 3
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- 2.0...+ 2.0 mg/H
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=> Page 01-77
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Different quantity injected Cyl. 4 and Cyl. 3
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- 2.0...+ 2.0 mg/H
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=> Page 01-77
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Evaluation: Idling speed smooth running control display
The injection system is equipped with an idling speed smooth running control. There may be power differences between the individual cylinders (component tolerances, injector delivery, compressions etc.) which are recognised and equalized via selective injected quantities.
Recognition at idling speed is via the signal from the engine speed sender which delivers four signals per crankshaft revolution to the control unit. If the signals are delivered at the same rhythm then all cylinders work the same. If one cylinder is weaker then the crankshaft takes longer for the next half revolution. Conversely a more powerful cylinder accelerates the crankshaft so less time is taken.
If the control unit recognises a difference, then the relevant cylinder is given more or less fuel, until the engine runs evenly again.
The measured value block displays the injected quantity differences of the individual cylinders compared with No. 3 cylinder that is required to ensure an even engine idling speed.
+... mg/H: The relevant cylinder is less powerful than No. 3 cylinder and is therefore supplied with more fuel.
-... mg/H: The relevant cylinder is more powerful than No. 3 cylinder and is therefore supplied with less fuel.
Display group 000 at full throttle (test drive in 3rd gear, coolant temperature not below 80 °C)
Notes:
-
◆ When testing, accelerate vehicle at full throttle.
-
◆ The measured values must be printed out or read (2nd person required) when the revolutions reach 3,000 rpm.
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Display group 000 (decimal displayed value)
|
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▪ Engine speed 2900...3100 rpm
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|
Read measured value block 0
|
◂ Indicated on display
|
|
|
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x
|
x
|
x
|
x
|
x
|
x
|
x
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x
|
x
|
x
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|
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|
1
|
2
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3
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4
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5
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6
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7
|
8
|
9
|
10
|
◂ Display zones
|
Specification
|
Corresponds to
|
|
|
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Air mass
|
225...255
|
750...850 mg/H
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Fuel temperature
|
91...201
|
20...80°C
|
|
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Intake manifold temperature
|
182...50
|
10...100°C
|
|
|
|
|
|
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|
|
Coolant temperature
|
80...35
|
80...110°C
|
|
|
|
|
|
|
|
Atmospheric pressure
|
Not relevant
|
---
|
|
|
|
|
|
|
Intake manifold pressure
|
165...189
|
1380...1575 mbar
|
|
|
|
|
|
Injected quantity
|
174...180
|
35...36 mg/stroke
|
|
|
|
|
Accelerator pedal position
|
255
|
100 %
|
|
|
|
Commencement of injection
|
138...188
|
8...12°BTDC
|
|
|
Engine speed
|
136...150
|
2850...3150 rpm
|
Display group 004 at full throttle (test drive in 3rd gear, coolant temperature not below 80 °C)
Notes:
-
◆ When testing, accelerate vehicle at full throttle.
-
◆ The measured values must be printed out or read (2nd person required) when the revolutions reach 3,000 rpm.
|
Display group 004 -Commencement of injection-
|
|
Read measured value block 4
|
⇒
|
◂ Indicated on display
|
|
|
|
xxxx rpm
|
xx.x °
B/ATDC
|
xx.x °
B/ATDC
|
xxx %
|
|
|
|
1
|
2
|
3
|
4
|
◂ Display zones
|
Specification
|
Evaluation
|
|
|
|
|
|
Commencement of injection valve duty cycle
|
60...90 %
|
=> Page 01-80
|
|
|
|
|
Commencement of injection (actual)
|
Approx. Commencement of inj. (specified)
|
=> Page 01-80
|
|
|
|
Commencement of injection (specified)
|
8...12°BTDC
|
---
|
|
|
Engine speed
|
2850...3150 rpm
|
---
|
Evaluation: Commencement of injection (actual) display
|
|
|---|
|
V.A.G 1551 display
|
Possible fault cause
|
Fault elimination
|
|
For large deviation from specified value (approx. 5°)
|
- Commencement of injection valve -N108 defective
|
- Check -N108 => Page 01-51, final control diagnosis
|
|
|
- Injection pump timing way off
|
- Check commencement of injection dynamically and adjust => Page 23-25
|
|
|
- Air in fuel system
|
- Check fuel supply system
|
Evaluation: Duty cycle from commencement of injection valve display
|
V.A.G 1551 display
|
Possible fault cause
|
Fault elimination
|
|
Below 60 or
above 90 %
|
- Commencement of injection valve -N108 defective
|
- Check -N108 => Page 01-51, final control diagnosis
|
|
|
|
- Check commencement of injection dynamically and adjust => Page 23-25
|
|
|
|
- Check fuel supply system
|
Display group 008 at full throttle (test drive in 3rd gear, coolant temperature not below 80 °C)
Notes:
-
◆ When testing, accelerate vehicle at full throttle.
-
◆ The measured values must be printed out or read (2nd person required) when the revolutions reach 3,000 rpm.
|
Display group 008 -Injected quantity limitation-
|
|
Read measured value block 8
|
⇒
|
◂ Indicated on display
|
|
|
|
xxxx rpm
|
xx.x mg/H
|
xx.x mg/H
|
xx.x mg/H
|
|
|
|
1
|
2
|
3
|
4
|
◂ Display zones
|
Specification
|
Evaluation
|
|
|
|
|
|
Injected quantity limitation due to mass of air drawn in (smoke prevention)
|
35...38 mg/H
|
=> Page 01-82
|
|
|
|
|
Injected quantity limitation via revs. (torque limitation)
|
34.2...35.2 mg/H
|
=> Page 01-82
|
|
|
|
Injected quantity (driver's requirement)
|
36...42 mg/H
|
=> Page 01-82
|
|
|
Engine speed
|
2850...3150 rpm
|
---
|
Evaluation: Injected quantity (driver's requirement) display
|
V.A.G 1551 display
|
Possible fault cause
|
Fault elimination
|
|
Below 36 mg/H
|
- No full throttle
|
- Repeat check at full throttle
|
|
|
- Accelerator pedal position sender -G79 incorrectly adjusted or defective
|
- Check G-79 and if necessary adjust
|
Evaluation: Injected quantity limitation via revs. (torque limitation) display
|
|
|---|
|
V.A.G 1551 display
|
Possible fault cause
|
Fault elimination
|
|
Below 34.2 mg/H
|
- Speed too high or too low
|
- Read off specified value at 3000 rpm
|
Evaluation: Injection quantity limitation due to air mass drawn in (smoke prevention) display
|
|
|---|
|
V.A.G 1551 display
|
Possible fault cause
|
Fault elimination
|
|
Below 35 mg/H
|
- Air mass drawn in insufficient
|
- Check exhaust gas recirculation and air mass meter function => Page 23-89
|
|
|
- Excessive exhaust gas recirculation
|
- Check exhaust gas recirculation and air mass meter function
|
Display group 010 at full throttle (test drive in 3rd gear, coolant temperature not below 80 °C)
Notes:
-
◆ When testing, accelerate the vehicle at full throttle.
-
◆ The measured values must be printed out or read (2nd person required) when the revolutions reach 3,000 rpm.
|
Display group 010 -Air quantities-
|
|
Read measured value block 10
|
⇒
|
◂ Indicated on display
|
|
|
|
xxx mg/H
|
xxxx mbr
|
xxxx mbr
|
xxx.x %
|
|
|
|
1
|
2
|
3
|
4
|
◂ Display zones
|
Specification
|
Evaluation
|
|
|
|
|
|
Accelerator pedal position
|
100 %
|
=> Page 01-85
|
|
|
|
|
Intake manifold pressure (charge pressure)
|
1720...1950 mbar
|
=> Page 01-85
|
|
|
|
Atmospheric pressure (ambient pressure)
|
No specification
|
---
|
|
|
Air mass drawn in
|
750...850 mg/H
|
=> Page 01-84
|
Evaluation: Air mass drawn in display
|
|
|---|
|
V.A.G 1551 display
|
Possible fault cause
|
Fault elimination
|
|
Below 750 mg/H
|
- Revs. too low or too high
|
- Read off specified value at 3000 rpm.
|
|
|
- Charge pressure too low
|
- Check charge pressure control
|
|
|
- Air mass meter defective
|
- Check exhaust gas recirculation and air mass meter function => Page 23-89
If a fault is present the measured value block indicates a constant air mass value of approx. 425 mg/H over the total speed and load range
|
Evaluation: Intake manifold pressure (charge pressure) display
|
V.A.G 1551 display
|
Possible fault cause
|
Fault elimination
|
|
Below 1720 mbar
|
- Charge pressure control defective
|
- Check charge pressure control
|
|
|
- Turbocharger defective
|
|
|
|
- Charge pressure limitation solenoid valve -N75 sticking
|
|
|
Above 1950 mbar
|
- Pressure hose of charge pressure control fallen off or blocked
|
- Check charge pressure control
=> Page 23-79
|
|
|
- Charge pressure limitation solenoid valve -N75 sticking
|
|
Evaluation: Accelerator pedal position display
|
|
|---|
|
V.A.G 1551 display
|
Possible fault cause
|
Fault elimination
|
|
Below 100 %
|
- No full throttle
|
- Repeat test at full throttle.
|
|
|
- Accelerator pedal position sender -G79 incorrectly adjusted or defective
|
- Check G-79 and if necessary adjust
|
Display group 011 at full throttle (test drive in 3rd gear, coolant temperature not below 80 °C)
Notes:
-
◆ When testing, accelerate the vehicle at full throttle.
-
◆ The measured values must be printed out or read (2nd person required) when the revolutions reach 3,000 rpm.
|
Display group 011 -Charge pressure control-
|
|
Read measured value block 11
|
⇒
|
◂ Indicated on display
|
|
|
|
xxxx rpm
|
xxxx mbr
|
xxxx mbr
|
xxx %
|
|
|
|
1
|
2
|
3
|
4
|
◂ Display zones
|
Specification
|
Evaluation
|
|
|
|
|
|
Duty cycle from charge pressure limitation valve
|
30...75 %
|
---
|
|
|
|
|
Charge pressure (actual)
|
1720...1950 mbar
|
=> Page 01-87
|
|
|
|
Charge pressure (specified)
|
1750...1950 mbar
|
---
|
|
|
Engine speed
|
2850...3150 rpm
|
---
|
Evaluation: Charge pressure display (actual)
|
V.A.G 1551 display
|
Possible fault cause
|
Fault elimination
|
|
Below 1720 mbar
|
- Charge pressure control defective
|
- Check charge pressure control
|
|
|
- Turbocharger defective
|
|
|
|
- Charge pressure hose not connected to control unit
|
- Connect charge pressure hose
|
|
Above 1950 mbar
|
- Pressure hose of charge pressure control fallen off or blocked
|
- Check charge pressure control
=> Page 23-79
|
|
|
- Charge pressure limitation solenoid valve -N75 sticking
|
|
| 
