Keep in mind:
- Internal deterioration of a catalytic converter is usually caused by abnormal engine operation upstream of the catalyst. Events that can produce higher than normal exhaust gas temperature (EGT) are particuarly suspect, such as misfiriring.
- Incorrect Ho2S signal input (e.g...
According to my factory service manual:
P0421 indicates Bank 1 catalyst system efficiency is below acceptable threshold.
POSSIBLE CAUSE
- Use of leaded fuel
- Oil contamination
- Cylinder misfiring
- Damaged Ho2 sensor
- Malfunctioning ECT/CHT sensor
- Downstream Ho2 sensor improperly...