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Checking ageing of lambda probe upstream of catalytic converter > < Checking Lambda control

A3 Mk1

Motronic injection and ignition system (4-cyl.)
Checking lambda control
Checking lambda probe and lambda control upstream of 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

Test requirements:

  • ● No faults stored in fault memory
  • ● No leaks in exhaust system
  • ● Coolant temperature at least 80 °C=>Display group 004, display zone 3

Checking operation

  • ‒ Connect vehicle diagnostic, testing and information system VAS 5051 or fault reader V.A.G 1551 and select engine electronics control unit with "address word" 01 .
    Engine must be idling.
 
→ Display readout:
Rapid data transfer     HELP
Select function XX
  • ‒ Enter "04" for "Start basic setting" function and confirm with Q key.

Checking lambda probe status
 
→ Display readout:
Basic setting    Q
Enter display group number XXX
  • ‒ Enter "030" for "Display group number 030" and confirm with Q key.
  • ‒ Check lambda probe status in display zone 1.

Note:

"Lambda probe status" indicates status of lambda control and lambda probe.

Display zones

1

2

3

4

Display group 030: Lambda probe status

Display

X X X

X X X

Readout

Lambda probe status bank 1, probe 1

Lambda probe status bank 1, probe 2

Operating range

0 = off
1 = on

0 = off
1 = on


Specification

1 1 1

1 1 1/0

Note

If reading does not match specification => Page 24-84

Significance of 3-digit display in display group 030

X

X

X

Display zone 1

1

Lambda control active

1

Lambda probe condition

1

Status of lambda probe heating

Notes:

  • ◆ First zone of 3-digit display (heating) fluctuates between 0 and 1.
  • ◆ "0" may also be displayed at idle (no load) for lambda control bank 1 probe 2.

Checking lambda probe learned values and control

  • ‒ Press C key.
 
→ Display readout:
Start basic setting    Q
Enter display group number XXX
  • ‒ Enter "032" for "Display group number 032" and confirm with Q key.
  • ‒ Check lambda probe learned values and control in display zones 1 and 2:

Display zones

1

2

3

4

Display group 032: Lambda learned values

Display

xx.x %

xx.x %

Readout

Lambda learned value
bank 1 at idle
(additive)

Lambda learned value
bank 1 at part throttle
(multiplicative)

Specification

-10.0...10.0 %
May fluctuate slightly

-10.0...10.0 %
May fluctuate slightly



Note

If reading does not match specification =>Evaluation of display group 032, Page 24-85

Evaluation of display group 032

Display zone: 1 / 2

Possible cause of trouble

Fault remedy

Lambda learned values
(mul.) less than -10.0 %

- Leakage in intake area

- Check intake system for leaks and eliminate unmetered air => Page 24-70

Lambda learned values
(add.) less than -10.0 %

- Oil dilution

- Change oil or drive across country at good speed

- High oil consumption level

- Air-mass meter defective

- Check air-mass meter => Page 24-61

- Activated charcoal filter solenoid valve sticking open

- Check activated charcoal filter solenoid valve => Page 24-132

- Fuel pressure too high

- Check fuel pressure regulator
=> Page 24-34

- Injector leaking

- Check injectors

- Lambda probe heating defective
- Lambda probe dirty

- Check lambda probe heating
=> Page 24-98

Evaluation of display group 032

Display zone: 1 / 2

Possible cause of trouble

Fault remedy

Lambda learned values (mul.) greater than 10.0 %

- Unmetered air in intake system

- Check intake system for leaks and eliminate unmetered air
=> Page 24-70

Lambda learned values (add.) greater than 10.0 %

- Fuel pressure too low

- Check fuel pressure regulator
=> Page 24-34

- Lambda probe heating defective

- Check lambda probe heating
=> Page 24-98

- Injector does not open or only partially

- Check injectors

- Activated charcoal filter solenoid valve sticking

- Check activated charcoal filter solenoid valve => Page 24-132
  • ‒ Press C key.
 
→ Display readout:
Start basic setting    Q
Enter display group number XXX
  • ‒ Enter "033" for "Display group number 033" and confirm with Q key.
  • ‒ Check 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

Readout

Lambda control
bank 1, probe 1

Lambda probe
voltage bank 1, probe 1

Specification

Value must fluctuate slightly in -20.0...20.0 % range

Voltage must fluctuate in 1.0...2.0 V range

Note

If reading does not match specification
=> Continued onPage 24-89

If reading does not match specification
=> Evaluation of display group 033,Page 24-88

Note on display zone 1:

Display must fluctuate around 0. If display is always 0, lambda control has switched from closed loop to open loop mode on account of a fault in the lambda control. Interrogate fault memory => Page 01-14.

Notes on display zone 2:

  • ◆ Voltage signal "Rich mixture (low residual oxygen level)" is less than 1.5 V.
  • ◆ Voltage signal "Lean mixture (high residual oxygen level)" is greater than 1.5 V.

Evaluation of display group 033

Display zone: 2

Possible cause of trouble

Fault remedy

Constant 1.5 V

- Open circuit in wire 1 between lambda probe and control unit

- Check basic voltage => Page 24-90

- Open circuit in wire 5 between lambda probe and control unit

Constant 4.9 V

- Short to positive in wire 1 between lambda probe and control unit

- Check wiring of lambda probe upstream of catalytic converter
=> Page 24-92

Constant 0.0 V

- Short to earth in wire 1 between lambda probe and control unit

Continued

If reading in display zone 1 does not match specification or if value does not fluctuate slightly:

  • ‒ Perform test drive to remove any residue from lambda probe and repeat test.

If reading in display zone 1 does not match specification even after a test drive or if value does not fluctuate:

  • ‒ Check basic voltage => Page 24-90.
  • ‒ Check lambda probe heating => Page 24-98.
  • ‒ Check for ageing of lambda probe upstream of catalytic converter
    .

Checking basic voltage
 
A26-0142
  • ‒ → Unscrew protective cover -arrows- on underside of vehicle.
 
M24-0053
  • ‒ → Unplug 6-pin connector -1- (black) for lambda probe upstream of catalytic converter -G39.
 
M24-0056
  • ‒ → Connect up multimeter for voltage measurement between contacts 1 and 5.
  • ‒ Switch on ignition.
    • ‒ Specification: 0.400 ... 0.500 V
  • ‒ Switch off ignition.

If reading does not match specification:

  • ‒ Check lambda probe wiring => Page 24-92.

Checking lambda probe wiring
 
A26-0142
  • ‒ → Unscrew protective cover -arrows- on underside of vehicle.
 
M24-0053
  • ‒ → Unplug 6-pin connector -1- (black) for lambda probe upstream of catalytic converter -G39.
  • ‒ Connect test box V.A.G 1598/31 to engine control unit wiring harness. Actual engine control unit is not to be connected.
 
M24-0056
  • ‒ → Check for open circuit in the following wiring.

Connector,

contact

Test box V.A.G 1598/31,
socket

1

70

2

71

5

51

6

52
  • ‒ Eliminate open circuit in wiring if necessary.
  • ‒ Check wiring for mutual short circuit.

If no fault is found in wiring:

  • ‒ Replace engine control unit => Page 24-16.

Checking ageing of lambda probe upstream of catalytic converter > < Checking Lambda control