P2423moderate severityPowertrain
HC Adsorption Catalyst Efficiency Below Threshold (Bank 1)
on 2003 Audi A6 3.0L V6 · AWD
What this code means
The hydrocarbon adsorption catalyst on bank 1 is not trapping and converting HC emissions effectively. This usually means the catalyst has degraded over time.
Symptoms
- Check engine light on
- Failed emissions test
- Reduced catalyst performance
Common causes
- Degraded or aged catalyst
- Exhaust leak upstream of catalyst
- Faulty oxygen sensor readings
- Engine running rich causing damage
Diagnostic steps
- Scan and verify related codes
- Inspect exhaust system for leaks
- Check oxygen sensor operation
- Replace catalyst if efficiency low
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