16555moderate severityPowertrain
System too Lean Bank 1
on 2009 Audi A3 2.0L TDI · FWD
What this code means
The ECU detects too much air or too little fuel in bank 1 (equivalent to OBD P0171). The mixture is running lean and trims are adding fuel to compensate.
Symptoms
- Check engine light on
- Rough idle
- Hesitation under acceleration
Common causes
- Vacuum or intake air leak
- Faulty mass air flow sensor
- Low fuel pressure or weak pump
- Dirty or clogged injectors
Diagnostic steps
- Read fuel trim values for lean bias
- Smoke test intake for leaks
- Test MAF sensor and fuel pressure
- Inspect and clean injectors
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