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Self-diagnosis
Reading measured value block: Display Groups 00 (block of ten) to 10
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Display group 00 (decimal displayed value)
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▪ Engine running at idling speed
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Display zones
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Specification
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Corresponds to
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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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Engine speed (idling speed)
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24...30
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760...960 rpm1)
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Injection period
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2...5
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2...5 ms
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Throttle valve angle
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2...16
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1...8 <°
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Operating status of lambda control
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see measured value block 99 2)
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Injection period (additive learned value) for lambda control
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0...50
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-0.5...+0.5 ms
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Lambda probe voltage
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0...50
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0.0...1.0 V
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Intake air mass
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18...52
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98...280 mg/stroke
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Coolant temperature
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170...205
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80...105 °C
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Engine control unit power supply voltage
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110...145
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11...14.5 V
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Intake air temperature
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70...160
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4.5...72 °C
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1) Up-to-date specifications:
=> Exhaust emissions test binder
2) Display zone 7 gives a decimal figure indicating the operating status of the lambda control. The operating status of the lambda control is represented by an 8-digit bit sequence in Display Group 99, display zone 4 .
Evaluating display group 00
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Display zone 1: Intake air temperature
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V.A.G 1551 readout
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Possible causes of fault
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Fault remedy
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lower than 70 1)
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- Intake air temperature sender
- Wiring for intake air temperature sender
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- Test intake air temperature sender
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higher than 160 1)
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Display zone 2: Engine control unit power supply voltage
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V.A.G 1551 readout
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Possible causes of fault
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Fault remedy
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lower than 110
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- Alternator defective, battery heavily discharged
- Heavy demand on electrical system shortly after starting due to high charging current and ancillaries
- Contact resistance in power supply or earth connection for engine control unit
- Current drain when ignition is switched off
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- Test voltage, charge battery
Increase revs slightly for a few minutes and switch off ancillaries
Test power supply to engine control unit
Eliminate current drain
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higher than 145
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- Voltage regulator in alternator defective
- Excess voltage from assisted start or high-speed charging
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- Test voltage; if necessary, fit a new voltage regulator
Interrogate fault memory
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1) Depends upon ambient temperature and time vehicle is parked.
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Display zone 3: Coolant temperature
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V.A.G 1551 readout
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Possible causes of fault
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Fault remedy
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lower than 170
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- Engine too cold
- Coolant temperature sender or wiring to engine control unit
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- Test drive if necessary
Test coolant temperature sender -G62
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higher than 205
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- Radiator dirty
- Radiator fan not working
- Coolant thermostat defective
- Coolant temperature sender or wiring to engine control unit
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- Clean radiator
Check operation of radiator fan
Test thermostat
Test coolant temperature sender -G62
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Display zone 4: Intake air mass
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V.A.G 1551 readout
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Possible causes of fault
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Fault remedy
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lower than 18
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- Large quantity of unmetered air between intake manifold and air mass meter
- Air mass meter or wiring to engine control unit
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- Eliminate leak
Test air mass meter
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higher than 52
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- Gear engaged (automatic gearbox)
- Engine load from ancillaries
- Air mass meter or wiring to engine control unit
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- Put selector lever in P or N position
Remove load (power assisted steering) or switch off ancillaries (e.g. air conditioner)
Test air mass meter
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Display zone 5: Lambda probe voltage
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V.A.G 1551 readout
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Possible causes of fault
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Fault remedy
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Readout not
alternating
(lambda control at rich or lean stop limit; see Display Group 99)
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- Large quantity of unmetered air
- Defective spark plug
- Fuel system pressure too high or too low
- Defective injector
- Coolant temperature sender -G62
- Solenoid valve 1 for activated charcoal filter -N80
- Lambda probe heating not working
- Lambda probe defective or dirty
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- Eliminate source of air leak
Test spark plugs
Test fuel system pressure and holding pressure
Read measured value block, Display Group 99
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DIsplay zone 5: Lambda probe voltage
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V.A.G 1551 readout
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Possible causes of fault
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Fault remedy
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constant 255
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- Short to positive through:
- Lambda probe -G39 or
- Signal wire or
- Engine control unit
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- Test lambda probe
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constant 80
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- Open circuit through:
- Lambda probe -G39 or
- Signal wire or
- Engine control unit
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- Test lambda probe
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constant 0
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- Short to earth through:
- Lambda probe -G39 or
- Signal wire or
- Engine control unit
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- Test lambda probe
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Display zone 6: Injection period (additive learned value) for lambda control (see also Display Group 11)
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V.A.G 1551 readout
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Possible causes of fault
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Fault remedy
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low lambda learned values
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- Lambda learned values low for idling and normal for part throttle; possibility of oil dilution (too much fuel in oil)
- Injector(s) leaking
- Fuel pressure too high
- Solenoid valve 1 for activated charcoal filter -N80 is constantly open
- Air mass meter -G70 defective
- Lambda probe heating defective or lambda probe dirty
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- See Display Group 11, display zones 2 and 3
Problem eliminated after motorway drive or oil change
Test injectors
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Display zone 6: Injection period (additive learned value) for lambda control
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V.A.G 1551 readout
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Possible causes of fault
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Fault remedy
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high lambda learned values
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- Lambda learned values high for idling and lower for part throttle; possibility of unmetered air around intake manifold
- Injector blocked
- Fuel pressure too low
- Unmetered air between -G70 and throttle valve
- Unmetered air at manifold gasket
- Lambda probe heating defective or lambda probe dirty
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- Eliminate faults
See Display Group 11, display zones 2 and 3
Check injection quantity
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Display zone 7: Operating status of lambda control
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- The operating status of the lambda control is represented by a bit sequence (8-digit number block) in Display Group 99, display zone 4.
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Display zone 8: Throttle valve angle
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V.A.G 1551 readout
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Possible causes of fault
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Fault remedy
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lower than 2
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- Throttle valve potentiometer in throttle valve control part -J338 defective or incorrectly adjusted
- Unmetered air between intake manifold and air mass meter, resulting in increased idling speed; the throttle valve control part will try to regulate the idling speed back to the specified level
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- Test throttle valve control part -J338
Eliminate sources of air leak
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higher than 16
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- Adaption of throttle valve control part -J338 not performed
- Throttle valve potentiometer in throttle valve control part -J338 defective or incorrectly adjusted
- Throttle cable incorrectly adjusted
- Throttle valve sticking
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- Perform adaption of throttle valve control part -J338
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Display zone 9: Injection period
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V.A.G 1551 readout
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Possible causes of fault
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Fault remedy
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lower than 2
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- Large quantity of fuel from the ACF system
- Wrong injectors installed (delivery rate too high)
- Fuel pressure regulator defective
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- Test solenoid valve for activated charcoal filter
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higher than 5
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- Increased engine load due to electrical consumers, air conditioner switched on, gear engaged, power assisted steering on full lock
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- Remove load
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Display zone 10: Engine speed (idling speed)
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V.A.G 1551 readout
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Possible causes of fault
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Fault remedy
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lower than 24
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- Throttle valve control part -J338 sticking or defective
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- Test throttle valve control part
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higher than 30
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- Throttle valve control part -J338 sticking or defective
- Large quantity of unmetered air; idling speed stabilisation can no longer compensate
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- Test throttle valve control part
Eliminate air leak
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Display Group 01: Basic values
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Read measured value block 1
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⇒
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◂ Indicated on display
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760...960
rpm
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80...105
°C
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0.00...1.00
V
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00000X10
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Throttle valve adaption requirements (see next page) 1)
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Lambda probe voltage - see Display Group 00
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Coolant temperature - see Display Group 00
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Engine speed (idling speed) - see Display Group 00
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1) The space marked with an "X" may contain either a 0 or a 1.
Note on display zone 4:
Relevance of figures in 8-digit number block for throttle valve adaption requirements:
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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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Significance when display = 1
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1
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Fault identified by self-diagnosis 2)
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1
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Signal from automatic gearbox
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1
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Air conditioner switched on
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1
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Idling speed switch open 1)
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1
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Fault in Lambda control
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1
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Throttle valve open (angle check) 1)
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1
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Engine running 1)
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1
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Coolant temperature less than 80 °C
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1) A figure "1" in this position means it will not be possible to perform an adaptation of the throttle valve control part.
2) A figure "1" in this position means that the self-diagnosis has identified a fault which may not yet have been recorded in the fault memory. If the self-diagnosis has identified a fault relating to the throttle valve control part it will not be possible to perform an adaption of the throttle valve control part using the "Basic setting" function.
Display Group 02: Basic values
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Read measured value block 2
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⇒
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◂ Indicated on display
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760...960
rpm
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100...280
mg/stroke
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0
km/h
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0100
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Operating status of engine
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Road speed
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Intake air mass - see Display Group 00
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Engine speed (idling speed) - see Display Group 00
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Note on display zone 4:
Significance of figures in 4-digit number block for operating status of engine:
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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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x
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Operating status of engine
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1
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Overrun
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1
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Idling
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1
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Part throttle
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1
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Full throttle
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Display Group 03: Basic values
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Read measured value block 3
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⇒
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◂ Indicated on display
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760...960
rpm
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100...280
mg/stroke
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1...8
<°
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-100...100
%
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Duty cycle of throttle valve positioner
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Throttle valve angle - see Display Group 00
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Intake air mass - see Display Group 00
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Engine speed (idling speed) - see Display Group 00
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Display Group 04: Basic values
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Read measured value block 4
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⇒
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◂ Indicated on display
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760...960
rpm
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100...280
mg/stroke
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2...5
ms
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1.8...5
g/s
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Intake air mass
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Injection period - see Display Group 00
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Intake air mass - see Display Group 00
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Engine speed (idling speed) - see Display Group 00
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Display Group 05: Basic values
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Read measured value block 5
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⇒
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◂ Indicated on display
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760...960
rpm
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11...14.5
V
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80...105
°C
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10...70
°C
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Intake air temperature - see Display Group 00
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Coolant temperature - see Display Group 00
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Engine control unit power supply voltage - see Display Group 00
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Engine speed (idling speed)
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Display Group 06: Altitude adaption
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Read measured value block 6
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⇒
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◂ Indicated on display
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760...960
rpm
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100...280
mg/stroke
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1...8
<°
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0.7...1.3
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Altitude correction factor
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Throttle valve angle
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Intake air mass - see Display Group 00
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Engine speed (idling speed) - see Display Group 00
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Display Group 07: Idling speed setting
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Read measured value block 07
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⇒
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◂ Indicated on display
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1...8
<°
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0.9...1.1
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0.9...1.1
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0100
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Operating status of engine
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Idling speed learned value (with gear engaged)
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Idling speed learned value (without gear engaged)
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Throttle valve angle
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Note on display zone 4:
Significance of figures in 4-digit number block for operating status of engine:
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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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x
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Operating status of engine
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1
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Overrun
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1
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Idling
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1
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Part throttle
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1
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Full throttle
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Note:
Measured value block 7 is for information only and has no significance for fault-finding in the workshop.
Display Group 08: Idling speed stabilisation
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Read measured value block 08
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⇒
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◂ Indicated on display
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760...960
rpm
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830...860
rpm
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-2...35
%
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1.8...5
g/s
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Intake air mass
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Idling speed stabiliser
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Specified idling speed when vehicle is stationary
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Engine speed (idling speed) - see Display Group 00
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Display Group 09: Idling speed air requirement
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Read measured value block 09
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⇒
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◂ Indicated on display
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-2..35
%
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0000
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80...105
°C
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760...960
rpm
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Engine speed
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Coolant temperature
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Throttle valve control part adaption status
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Idling speed stabiliser
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Note on display zone 2:
Relevance of figures in 4-digit number block for adaption status of throttle valve control part:
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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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Adaption status
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1
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A fault has occurred during adaption of the throttle valve control part; interrogate fault memory => Page 01-10
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1
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No current in throttle valve control part (duty cycle = 0)
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1
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Adaption terminated because battery voltage is too low (less than 8V)
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1
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Idling speed switch open (switch position check)
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Display Group 10: Lambda control and ACF system
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Read measured value block 10
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⇒
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◂ Indicated on display
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-25...25
%
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0.00...1.00
V
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0...10
%
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-10...15
%
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Lambda correction factor with active fuel tank breather system
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Duty cycle of solenoid valve 1 for activated charcoal filter -N80
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Lambda probe voltage
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Lambda control
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Note:
Measured value block 10 is for information only and has no relevance for fault-finding in the workshop.
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