P0172

DIAGNOSTIC TROUBLE CODES P0171, PO172
Adaptation too lean or too rich, rear cylinder row (cyl. 1-3- 5)

Fault Symptom.
CHECK ENGINE lamp (MIL) on

Condition
More than 25% richer or leaner for at least 20 seconds

Diagnostic Procedure.
If other diagnostic trouble codes are present, deal with them first.
1. Activate the ISAT command "ADAPT. SHORT 1-3-5" or "ADAPT. LONG 1-3-5" in the "READ FUNCTIONS" menu to see whether the engine is running on a lean or rich mixture. Lambda 1 corresponds to 0% on the ISAT.

"ADAPT. SHORT" displays the current fuel-air mixture and "ADAPT. LONG" shows the mean value of the mixture over the past 15-20 minutes.

2. Clear all trouble codes and drive the car to check whether any trouble codes are generated afresh. It they are, continue as described below.

3. Check the following points:
- that the oxygen sensor's signal lead is not in contact with any HT lead
- that components of the correct type are fitted in the fuel system
- that no air leakage occurs in the induction system
- that fuel pressure is correct
- that battery voltage is correct
- that no leakage occurs in the exhaust system ahead of or behind the oxygen sensor
- that all grounding points in the system are OK

4. If no faults can be detected after carrying out the above checking procedure, clear all trouble codes and drive the car on the road to check whether any trouble codes are generated afresh.

If they are, continue at "Before Replacing Control Module" for further diagnostic instructions. Before Replacing A Control Module