Audi Workshop Service and Repair Manuals

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/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.

Special tools, testers and auxiliary items

• ◆ Fault reader V.A.G 1551 (or vehicle system tester V.A.G 1552) with cable V.A.G 1551/3

Testing vehicle under cold-start conditions:

• ‒ Connect fault reader V.A.G 1551
  .
• ‒ Start the engine.
• ‒ Select "Read measured value block", Display Group 009, engine at idling speed.

Display zone 1 will show the signal voltage for lambda probe 1.

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

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

• ‒ Take vehicle for a test drive.

• ‒ Observe display zones 1 and 2 during test drive.

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 only becomes poor after the lambda control has cut in, test operation of lambda probes
  => Page 24-68.

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", Display Group 008, engine at idling speed. If the values are not as specified, rectify the fault.

• ‒ Check also the measured value blocks in function 04 (Basic setting). The solenoid valve for the activated charcoal filter -N80 is closed for this function.

• ◆ The lambda control can be switched on and off as required using Display Group 099. Press keys 4 and 8 to switch back and forth between "Basic setting " (lambda control off) and "Read measured value block" (lambda control on).