All trouble codes → Catalytic converter efficiency codes
Catalytic converter efficiency codes
This code sets when the downstream oxygen sensor starts to mirror the upstream one — a sign the catalytic converter has lost efficiency. A worn converter is one cause, but an upstream misfire, a rich condition or an exhaust leak can damage or fake it, so rule those out before spending money on a converter.
Emissions fault — will fail inspection. Rule out misfires, exhaust leaks and O2 sensor issues before replacing the converter.
Common causes
- Worn catalytic converter
- Upstream misfire or rich condition damaged the catalyst
- Exhaust leak near the O2 sensors
- Lazy/biased downstream O2 sensor
First checks
- Fix any misfire and fuel trim issues first
- Compare upstream vs downstream O2: the downstream sensor should stay steady (~0.6–0.7 V) while the upstream switches
- Check Mode $06 catalyst results for margin
System: Auxiliary emission controls. This is general guidance for the generic OBD-II codes in this group; always confirm against the service information for your specific vehicle.
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