P0421

P0421

Diagnostic information - DME (DFI)

Catalytic converter, bank 1, inadequate effect

Diagnostic conditions
- Perform following short tests in sequence:
1. All models: Oxygen-sensor short tests
2. Short test Tank vent
3. Short test Fuel supply Partial load
4. Short test Fuel supply Idle speed
5. Short test Catalytic-converter conversion

or:

- Engine temperature more than 60 °C (140 °F)
- Time after engine starts more than 10 seconds
- Catalytic converter temperature 500 °C ... 750 °C (932 °F ... 1,382 °F)
- Driving for an extended period with gentle acceleration at 30 ... 130 km/h (19 ... 81 mph)
- Loading of carbon canister less than 0.7
- Engine speed less than 3,000 rpm
- Lambda control ahead of catalytic converter active
- Lambda control behind catalytic converter ready for operation
- No detection of oxygen sensor, mass air flow sensor or throttle valve adjusting unit fault

Possible fault causes
- If an oxygen sensor fault is entered::
- corresponding fault cause
- Remedy oxygen-sensor fault according to instructions then
- then perform short test as described above


- Leak in exhaust system between engine and oxygen sensor behind catalytic converter --> this is particularly relevant when driving with a mass air flow less than 250 mg/stroke
- Oxygen sensors ahead of and behind catalytic converter bank 1 are interchanged
- Catalytic converter bank 1 faulty