Catalyst System Efficiency Below Threshold (Bank 2)
What it means
This is the bank 2 version of P0420 and appears on engines with two cylinder banks. The computer sees that the sensor after the converter reads almost the same as the one before it, meaning the converter is not doing its job.
Symptoms4
- Check engine light, usually with no other symptom.
- Occasional sulfur smell from the exhaust.
- Reduced performance if the converter is clogged.
- Failed periodic inspection.
Possible causes5
- Worn catalytic converter on bank 2.
- Faulty bank 2 downstream oxygen sensor.
- Exhaust leak on bank 2.
- Earlier misfires on bank 2 cylinders.
- Engine burning oil or coolant.
How to diagnose and fix5
- Fix any misfire or fuel mixture codes first.
- Check for exhaust leaks on bank 2.
- Compare downstream and upstream sensor readings with a scan tool.
- Replace the downstream sensor if it is proven faulty.
- Replace the converter after ruling out other causes.
Repair cost
In Saudi riyals; the highlighted part is the expected range for this fault.
It starts at the cost of a sensor or leak repair and can exceed 5,000 SAR if a genuine converter is required.
Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Frequently asked questions
P0420 and P0430 appeared together. Are both converters bad?
Possibly, but both at once suggests a shared cause such as combustion problems or oil burning. Check for that before replacing both.
Will an aftermarket converter do?
Good-quality aftermarket units can work, but very cheap ones often let the code return soon.
This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.
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