P0409moderate severityPowertrain
Exhaust Gas Recirculation Sensor A Circuit
on 2003 Audi A6 3.0L V6 · AWD
What this code means
There is a fault in the EGR position sensor circuit. This prevents the PCM from knowing how far the EGR valve is open, affecting emissions.
Symptoms
- Check engine light on
- Rough idle
- Failed emissions test
Common causes
- Faulty EGR position sensor
- Wiring or connector problems
- Carbon-clogged EGR valve
- Bad PCM
Diagnostic steps
- Read code and freeze frame data
- Inspect EGR sensor wiring and connector
- Test sensor voltage and ground
- Replace EGR sensor or valve as needed
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