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Testing lambda probe (before catalytic converter) for ageing > < Testing lambda control (engine code: AVV)

A4 Mk1

Motronic injection and ignition system (4-cyl.)
Testing lambda control (engine code: AVV)
Testing lambda probe and lambda control (before catalytic converter)

Special tools and workshop equipment required

  • ◆ V.A.G 1526 A
  • ◆ V.A.G 1594 A
  • ◆ V.A.G 1598/31
  • ◆ VAS 5051 with VAS 5051/1
  • or
  • ◆ V.A.G 1551 with V.A.G 1551/3 A

Requirements for test:

  • ● Exhaust system free of leaks
  • ● Coolant temperature at least 80 °C

Test sequence

  • ‒ Connect vehicle diagnostic, testing and information system VAS 5051 (or fault reader V.A.G 1551) and select engine electronics control unit by entering address word "01" ( .)
    When doing this the engine must be idling.
 
→ Indicated on display:
Rapid data transfer     HELP
Select function XX
  • ‒ Enter "04" to select "Basic setting" and confirm with Q key.
 
→ Indicated on display:
Basic setting    Q
Enter display group number XXX
  • ‒ Enter "030" to select Display Group 030 and confirm entry with Q key.
  • ‒ Check readout in display zone 1.

Notes:

  • ◆ The specified readouts can be obtained more quickly by increasing the engine speed.
  • ◆ The "lambda probe status" indicates the status of the lambda control and the lambda probes.

Display zones

1

2

3

4

Display Group 030: Lambda probe status

Display

X X X

XXX

Indicates

Lambda probe status Bank 1, probe 1

Lambda probe status
Bank 1, probe 2

Range

0 = off
1 = on

0 = off
1 = on


Specification

1 1 1

110

Note

If readout does not match specification => Page 24-83.

Significance of three-digit display in Display group 030

X

X

X

Display zones 1 and 2

X

Lambda control : 0= inactive; 1= active

X

Lambda probe condition: 0= inactive; 1= active

X

Status of lambda probe heating: 0= inactive; 1= active

Note:

The first digit in this three-digit display (heating) fluctuates between 0 and 1.

  • ‒ Do not continue test until display "111" has been indicated in display zone 1 at least once.

Testing lambda probe learned values and lambda control

  • ‒ Press C key.
 
→ Indicated on display:
Basic setting    Q
Enter display group number XXX
  • ‒ Enter "032" to select Display Group 032 and confirm entry with Q key.
 
→ Indicated on display:
Basic setting 32    ⇒
    1    2    3    4
  • ‒ Check lambda learned values in display zones 1 and 2.

Display zones

1

2

3

4

Display Group 032: Lambda learned values

Display

xx.x %

xx.x %

Indicates

Lambda learned value, Bank 1, Probe 1
at idling speed (additive)

Lambda learned value, Bank 1, Probe 1 at part throttle (multiplicative)

Specification

-6.0...6.0 %

-10.0...10.0 %



Note

If the specification is not attained

  • ‒ Press C key.
 
→ Indicated on display:
Basic setting    Q
Enter display group number XXX
  • ‒ Enter "033" to select Display Group 033 and confirm entry with Q key.
 
→ Indicated on display:
Basic setting 33    ⇒
    1    2    3    4
  • ‒ Check readouts for lambda control in display zones 1 and 2.

Display zones

1

2

3

4

Display Group 033: Lambda control

Display

xx.x %

x.xxx V

Indicates

Lambda control
Bank 1, Probe 1

Lambda probe voltage Bank 1, Probe 1

Specification

The readout should fluctuate by at least 2 % in a range between -10.0...10.0 %

0.130...3.600 V

Note

If readout does not match specification
=>Further notes,
Page 24-86

If readout does not match specification
=>Reading Display Group 033, Page 24-89

Note on display zone 2:

The display indicates the lambda probe voltage signal after it is processed and smoothed by the engine control unit. A display of 1.5 V equals lambda 1.

Further notes

If the readout in display zone 1 does not match the specification, or if the readout does not fluctuate by at least 2 %:

  • ‒ Take car for a test drive to free lambda probe of any deposits, then repeat the test.

If the readout in display zone 1 still does not match the specification even after the test drive, or if the readout still does not fluctuate by at least 2 %:

  • ‒ Test the basic voltage => Page 24-90.
  • ‒ Test the lambda probe heating before catalytic converter.
  • ‒ Check the lambda probe (before the catalytic converter) for ageing => Page 24-93

Reading Display Group 032

Display zone 1 / 2

Possible cause of fault

Fault remedy

Lambda learned
values below specified range

- Air leak in intake system

- Check intake system for leaks and eliminate unmetered air

- Oil dilution

- Change oil or drive car
at moderate to high speeds on
out-of-town roads

- High oil consumption

- Air mass meter defective

- Test air mass meter
=> Page 24-43

- Solenoid valve for activated charcoal filter sticking in open position

- Test solenoid valve for activated
charcoal filter => Page 24-131

- Fuel pressure too high

- Test fuel pressure regulator
=> Page 24-20

- Injector does not close

- Test injectors => Page 24-31

- Lambda probe heating defective
- Lambda probe defective

- Test lambda probe heating
=> Page 24-97

Reading Display Group 032

Display zone 1 / 2

Possible cause of fault

Fault remedy

Lambda learned
values above specified range

- Unmetered air in intake tract

- Check intake system for leaks and eliminate unmetered air

- Fuel pressure too low

- Test fuel pressure regulator
=> Page 24-20

- Air mass meter defective

- Test air mass meter
=> Page 24-43

- Lambda probe heating defective
- Lambda probe defective

- Test lambda probe heating
=> Page 24-97

- Injector not opening or only opening partially

- Test injectors => Page 24-31

- Solenoid valve for activated charcoal filter sticking

- Test solenoid valve for activated
charcoal filter => Page 24-131

Reading Display Group 033

Display zone 2

Possible cause of fault

Fault remedy

Above 4.800 V

- Short to positive in wire between lambda probe and control unit
- Lambda probe defective

- Test lambda probe wiring (lambda probe before catalytic converter) => Page 24-91

Less than 0.130 V

- Short to earth in wiring between lambda probe and control unit
- Lambda probe defective

- Replace lambda probe before catalytic converter

Testing basic voltage
 
A24-0392
  • ‒ → Unplug 6-pin connector (black) for lambda probe (before catalytic converter) -G39.

Note:

For access to connector, unscrew bolts securing coolant expansion tank and pivot expansion tank clear to the side. The coolant hoses do not have to be disconnected.
 
A24-0139
  • ‒ → Connect multimeter (voltage measurement range) between contacts 1 and 5.
  • ‒ Switch ignition on.
    • ‒ Specification: 0.400 ... 0.500 V
  • ‒ Switch off ignition.

If the specification is not obtained:

  • ‒ Test lambda probe wiring.

If the specification is obtained:

  • ‒ Replace the lambda probe (before catalytic converter) -G39.

Testing lambda probe wiring
 
A24-0392
  • ‒ → Unplug 6-pin connector (black) for lambda probe (before catalytic converter) -G39.

Note:

For access to connector, unscrew bolts securing coolant expansion tank and pivot expansion tank clear to the side. The coolant hoses do not have to be disconnected.

  • ‒ Connect test box V.A.G 1598/31 to wiring harness for engine control unit. Do not connect to the engine control unit itself.
    => Page 24-10.
 
A24-0139
  • ‒ → Test the following wiring connections for open circuits:

Connector
Contact

Test box V.A.G 1598/31
Socket

1

70

2

71

5

51

6

52
  • ‒ Rectify any open circuits.

=> Current flow diagrams, Electrical fault finding and Fitting locations binder

  • ‒ Test for short circuits between the wires.

If the wiring is OK:

  • ‒ Fit a new engine control unit => Page 24-13.

Testing lambda probe (before catalytic converter) for ageing > < Testing lambda control (engine code: AVV)