DTC P0420: Catalyst System Efficiency Below Threshold: Condition
WARNING: This page is about a different car, the 2002 Suzuki Esteem. However, it is still accessible from the selected car via links, so may be relevant.
DTC is set when while vehicle is being driven at constant speed other than at a high load, value from HO2S No. 2 becomes closer to value from HO2S No. 1. ECM monitors this circuit once per drive cycle. MIL is illuminated when ECM detects malfunction during 2 consecutive drive cycles. Possible causes are:
- Exhaust system leak.
- Catalytic converter malfunction.
- Fuel system malfunction.
- HO2S No. 1 malfunction.
- HO2S No. 2 malfunction.