P0421
Warm Up Catalyst Efficiency Below Threshold Bank 1
1999-2000 BMW 323i E46 2.5L I6
Moderate SeverityPowertrainGeneric (SAE)
Description
The Bank 1 warm-up catalytic converter is not efficient during the warm-up period.
Symptoms
- Check Engine Light
- Failed emissions test
Common Causes
- Worn catalyst
- Engine running rich during warm-up
- O2 sensor issue
- Exhaust leak
Diagnostic Steps
- Monitor catalyst temps during warm-up
- Compare O2 sensor signals
- Check for exhaust leaks
Repair Notes
Replace warm-up catalyst if confirmed failed.
Related Codes
Other Powertrain Codes
- P0001Fuel Volume Regulator Control Circuit/Open
- P0002Fuel Volume Regulator Control Circuit Range/Performance
- P0003Fuel Volume Regulator Control Circuit Low
- P0004Fuel Volume Regulator Control Circuit High
- P0010Intake Camshaft Position Actuator Circuit/Open Bank 1
- P0011Intake Camshaft Position Timing Over-Advanced Bank 1
- P0012Intake Camshaft Position Timing Over-Retarded Bank 1
- P0013Exhaust Camshaft Position Actuator Circuit/Open Bank 1
- P0014Exhaust Camshaft Position Timing Over-Advanced Bank 1
- P0015Exhaust Camshaft Position Timing Over-Retarded Bank 1
P0421 on Other Vehicles
Common Questions
What does code P0421 mean on a 1999-2000 BMW 323i E46?
P0421 stands for "Warm Up Catalyst Efficiency Below Threshold Bank 1". The Bank 1 warm-up catalytic converter is not efficient during the warm-up period.
What are the symptoms of P0421 on a BMW 323i E46?
Common symptoms of P0421 include: Check Engine Light, Failed emissions test.
What causes P0421 on a 1999-2000 BMW 323i E46?
Common causes of P0421 include: Worn catalyst, Engine running rich during warm-up, O2 sensor issue, Exhaust leak.