Audi Workshop Service and Repair Manuals

Test requirements:

No fault stored relating to the lambda control - if necessary eliminate fault(s) and clear the fault memory.

The time that elapses before the lambda control cuts in (required probe temperature approx. 300 oC) is mainly influenced 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.

Procedure:

Check the vehicle under cold start conditions.

• ‒ Read measured value block (function 08) and select Display group 07 =>Page 01-49.

Display zone 2 will show the voltage of the lambda probe signal.

Engine cold or lambda control not running: 0.45...0.50 V.

• ‒ Start engine and carry out a road test, observe Display zone 2 during the road test.

Voltages of more than +0,7 V indicate a rich fuel mixture (low oxygen level in exhaust gas).

Voltages of less than +0.3 V indicate a lean fuel mixture (high oxygen level in 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 engine performance is only poor after the lambda control has cut, check its operation =>Page 24-42.

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 08. If the values are not as specified, rectify the fault.
• ‒ Also check the measured value blocks in function 04 (Basic setting). The ACF solenoid valve -N80 is closed for this function.

• ◆ With the aid of Display group 99 it is possible to switch the lambda control on and off as required. Pressing keys 4 and 8 will switch between the "Basic setting" (lambda control off) and "Read measured value block" (lambda control on).