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Testing operation > < Testing lambda control

A3 Mk1

Simos Injection and Ignition System (4-cylinder)
Testing lambda control
Poor performance after cold start

Test conditions

  • ● No faults relating to lambda control function recorded in fault memory. If faults are recorded, rectify them and erase the fault memory.

The time it takes for the lambda control to cut in (lambda probe temperature must be approx. 300°C) is mainly determined by the following factors.

  • ◆ Ambient temperature (summer or winter)
  • ◆ Operating conditions after starting
  • ◆ Functioning of lambda probe heating

If faults occur after a cold start, check whether the problem arises before or after the lambda control cuts in.

Testing vehicle under cold start conditions:

  • ‒ Select function 08 "Read measured value block" and Display Group 99
    =>Page 01-103.
 
→ Display readout:
Read measured value block 99    ⇒
    1    2    3    4

Display zone 4 will show the status of the Lambda control.

Relevance of figures in 8 digit number block in display zone 4 (see also Page 01-103):

Display zone 4

Meaning of readout

1XXXXXXX

Fault recorded in memory during diagnosis

X1XXXXXX

Not allocated

XX1XXXXX

Not allocated

XXX1XXXX

Restricted operation mode

XXXX1XXX

Lambda control at stop limit

XXXXX1XX

Lambda control switched on

XXXXXX1X

Lambda probe functioning

XXXXXXX1

Mixture status
1 = rich mixture
0 = lean mixture

After cold start:
 
→ Display readout:
Read measured value block 99    ⇒
    1    2    3    XXXXX00X

Notes:

  • ◆ The lambda probe will not start functioning immediately after a cold start (lambda probe too cold).
  • ◆ The lambda control is activated once the lambda probe is functioning.
Important!
The V.A.G 1551 must be operated by a second person.
  • ‒ Take the vehicle for a test drive and watch display zone 4.
 
→ The lambda control cannot cut in unless it is switched on and the lambda probe is functioning.
Read measured value block 99    ⇒
    1    2    3    XXXXX11X

The readout for the mixture status (on the far right of the 8 digit number block) should fluctuate continuously between "0" and "1".

A "1" in the space for "Mixture status" indicates that the air/fuel mixture is too rich (too little residual oxygen in the exhaust gas).

A "0" in the space for "Mixture status" indicates that the air/fuel mixture is too lean (too much residual oxygen in the exhaust gas).

  • ‒ If the engine performance is poor before the lambda control cuts in, the lambda control is not the cause of the problem.
  • ‒ If the performance only becomes poor after the lambda control has cut in, test the operation of the lambda control
    =>Page 24-52.

Notes:

  • ◆ If the performance improves once the lambda control has cut in, this means that the lambda control is counteracting the problem (e.g. unmetered air or defective injector, etc.). Check the lambda learned values to confirm this.
  • ‒ Select "Read measured value block" (function 08) and Display Group 11.
  • ‒ Compare the actual values (displayed on the test apparatus) with the specifications.

Testing operation > < Testing lambda control