Catalyst 1/1 Efficiency Failure (OBD II)

Name of Code:
Catalytic Converter Efficiency Failure

When Monitored:
See DRB III

Set Condition:
See DRB III

Theory of Operation:
The catalyst monitor uses oxygen sensors (O2S's) to monitor the efficiency of the converter. The dual O2S strategy is based on the fact that as a catalyst deteriorates, its oxygen storage capacity and its efficiency are both reduced. By monitoring the oxygen storage capacity of a catalyst, its efficiency can be indirectly calculated. The upstream O2S is used to detect the amount of oxygen in the exhaust gas before the gas enters the catalytic converter. As the converter absorbs the oxygen, there is lack of oxygen downstream of the converter and the output of the downstream O2S indicates limited activity. The downstream O2S detects oxygen content in treated gases that passed the converter. The PCM monitors lean-to-rich switches of the dual O2S's. A ratio of downstream to upstream switches closer too indicates an operational catalyst. while a 1:1 ratio indicates an ineffective catalyst.

Probable causes:
- Catalytic converter
- Exhaust leaks upstream of catalyst
- Contaminated fuel
- Mechanical engine problem
- Weak O2 sensor with a deteriorated catalyst