Can a faulty catalytic converter cause the check engine light in my Mercedes-Benz E-Class to turn on?

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Can a faulty catalytic converter cause the check engine light in my Mercedes-Benz E-Class to turn on?

The check engine light came on in my E-Class, and a mechanic mentioned it might be due to the catalytic converter. How does a failing o r inefficient catalytic converter trigger this warning? What other components should I check before replacing the converter?

Talha Kyanii asked on 11 Oct 2025 13:44:59 pm

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Gari Master - on 11 Oct 2025 13:45:45 pm

Yes, a faulty o r inefficient catalytic converter is a common cause of the check engine light CEL in Mercedes-Benz E-Class models. Heres how:

The oxygen sensors O2 sensors monitor emissions before and after the catalytic converter.

If the converter is not reducing harmful gases properly, the sensors detect abnormal levels of CO, NOx, o r unburnt hydrocarbons.

This triggers the P0420 o r P0430 error code catalyst efficiency below threshold, causing the CEL to come on.

Other Things to Check First:

O2 sensors themselves — sometimes the sensor is faulty, not the converter.

Vacuum leaks o r misfires — these can cause temporary poor emissions.

Oil o r coolant leaks into the exhaust — often mistaken as a bad cat.

What to Do:
Have a diagnostic scan done to read the fault codes. If it’s a P0420/P0430, your mechanic should test the catalytic converter efficiency before replacing it — since the part is expensive.