P0421 OBD Trouble Code
1 result found
| Type | Powertrain - Auxiliary Emission Controls - ISO/SAE Controlled |
|---|---|
| Description | Catalyst System Efficiency Below Threshold Conditions |
| Cause | Engine running at steady state highway conditions for 5 minutes in closed loop, then the PCM detected that the rear HO2S switch rate was too high |
Try also: https://www.obd-codes.com/p0421
