17964moderate severityPowertrain
Charge Pressure Control: Negative Deviation
on 2009 Audi A3 2.0L TDI · FWD
What this code means
Actual turbo boost pressure is lower than the target commanded by the ECU. Equivalent to OBD-II code P1556.
Symptoms
- Reduced power / limp mode
- Turbo lag or no boost
- Check engine light on
Common causes
- Boost leak in charge pipes or hoses
- Faulty wastegate or actuator
- Stuck or leaking diverter/N75 valve
- Faulty boost pressure sensor
Diagnostic steps
- Read boost target vs actual values
- Pressure test charge air system for leaks
- Check wastegate/actuator operation
- Test N75 valve and boost sensor
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