P0405moderate severityPowertrain
EGR Sensor A Circuit Low
on 2004 Audi S4 4.2L V8 · AWD
What this code means
Low voltage from the EGR position sensor A.
Symptoms
- Check Engine Light
- EGR control issues
Common causes
- Short to ground in sensor circuit
- Faulty sensor
- Wiring damage
Diagnostic steps
- Test sensor voltage
- Check for shorts
- Inspect wiring
Repair notes
Repair wiring or replace EGR valve (sensor often integrated).
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