Catalyst System Efficiency Below Threshold (Bank 1)
What it means
The computer compares the oxygen sensor readings before and after the catalytic converter and found that the converter is no longer cleaning the exhaust well enough. The converter may really be worn, or the fault may be the downstream sensor or an exhaust leak.
Symptoms4
- Check engine light, usually with no other symptom.
- Occasional rotten egg smell from the exhaust.
- Loss of power if the converter is clogged.
- Failed emissions or periodic inspection.
Possible causes5
- Aged or worn-out catalytic converter.
- Faulty downstream oxygen sensor giving false readings.
- Exhaust leak near the sensors.
- Past misfires that damaged the converter.
- Oil or coolant being burned in the engine and contaminating the converter.
How to diagnose and fix6
- First fix any stored misfire or rich/lean codes.
- Inspect the exhaust for leaks before and after the converter.
- Watch the downstream sensor reading; it should be fairly steady, not switching like the upstream one.
- Test the downstream sensor and replace it if faulty.
- Make sure the engine is not burning oil or coolant.
- Replace the converter only after ruling out the causes above.
Repair cost
In Saudi riyals; the highlighted part is the expected range for this fault.
The range is wide: a sensor or exhaust leak repair is cheap, while a genuine converter on some cars exceeds 5,000 SAR.
Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Frequently asked questions
Should I replace the converter right away?
No. It is expensive, and many cases turn out to be a sensor or a leak. Replacing it without fixing what killed it will ruin the new one too.
Can I drive with this code?
Usually yes, unless you notice severe power loss or unusual heat under the car, which suggests a blockage that needs prompt inspection.
Is removing the converter an acceptable fix?
No. It breaks emissions regulations in most countries, fails inspections and triggers other codes.
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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