P0422moderate severityPowertrain
Main Catalyst Efficiency Below Threshold (Bank 1)
on 2000 BMW 528i 2.8L I6 M52 · RWD
What this code means
The PCM determined the main catalytic converter on bank 1 is not reducing emissions efficiently. This is usually judged by comparing upstream and downstream oxygen sensor readings.
Symptoms
- Check engine light on
- Failed emissions test
- Reduced fuel economy
Common causes
- Failed catalytic converter
- Faulty downstream O2 sensor
- Exhaust leak
- Engine misfire or fuel issue
Diagnostic steps
- Scan and confirm P0422
- Compare upstream and downstream O2 data
- Inspect exhaust for leaks
- Test catalyst efficiency
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Other Powertrain codes on this vehicle
29CC
Misfire Cylinder 1
29CD
Misfire Cylinder 2
29CE
Misfire Cylinder 3
29CF
Misfire Cylinder 4
29D0
Misfire Cylinder 5
29D1
Misfire Cylinder 6
29D2
Misfire Cylinder 7
29E0
Lambda Additive/Idle Adaptation Limit, Bank 1
29E1
Lambda Additive/Idle Adaptation Limit, Bank 2
29E2
Lambda Multiplicative Part-Load Adaptation Limit, Bank 1