16804moderate severityPowertrain
Catalyst System Efficiency Below Threshold Bank 1
on 2003 Audi A6 3.0L V6 · AWD
What this code means
The catalytic converter on bank 1 is not cleaning exhaust efficiently (OBD P0420). This usually means a degraded catalyst or sensor issue.
Symptoms
- Check engine light
- Failed emissions test
- Reduced fuel economy
Common causes
- Degraded catalytic converter
- Faulty rear O2 sensor
- Exhaust leak
- Engine running rich or lean
Diagnostic steps
- Read fault codes
- Compare front/rear O2 signals
- Inspect exhaust for leaks
- Test or replace catalyst
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16515
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