P0239moderate severityPowertrain
Turbocharger/Supercharger Boost Sensor B Circuit Range/Performance
on 2009 Audi A8 4.2L V8 · AWD
What this code means
The PCM has detected that the turbo/supercharger boost sensor B signal is outside the expected range. This usually points to a sensor or wiring fault affecting boost pressure readings.
Symptoms
- Reduced engine power
- Check engine light on
- Poor acceleration
Common causes
- Faulty boost pressure sensor
- Damaged sensor wiring or connector
- Boost/vacuum leak
- Restricted sensor reference hose
Diagnostic steps
- Scan and record freeze frame data
- Inspect boost sensor wiring and connector
- Compare sensor reading to actual boost
- Replace boost sensor if out of spec
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