A clogged catalytic converter creates back-pressure in the exhaust: the engine "cannot breathe", loses power and runs hotter. If it is merely worn out, the typical error is P0420 for efficiency below threshold.
Typical symptoms
- Gradual loss of power, especially at high revs
- Acrid, rotten-egg smell
- Rising consumption and high temperatures under the car
- Check engine light with code P0420 or P0430
- Metallic rattle from the exhaust if the substrate has crumbled
- Difficulty revving up, as if the car were "braked"
Why it is ruined
- Prolonged rich mixture (injectors, lambda sensor, MAF)
- Repeated misfires that melt the substrate
- Oil consumption from rings or turbo
- Impact or corrosion of the casing
- Non-compliant additives and poor fuel
How it is checked
- Back-pressure measurement in the exhaust: the most reliable test for blockage.
- Upstream versus downstream lambda comparison: if the signals are similar, the converter is no longer working.
- Temperature check at inlet and outlet.
- Fuel trim reading to rule out a rich mixture that is ruining it.
What not to do
Replacing the converter without fixing the upstream cause ruins the new one too. If the fault is a dripping injector or a defective sensor, the new part is damaged in a short time. For costs see how much it costs to replace the catalytic converter.
Can you drive with a clogged converter?
Better to avoid it: high back-pressure strains the engine and can damage valves and turbo. On a turbo car the risk is even greater.
How MasterTuning helps
We read the real values of the control unit, not just the code: that is the difference between finding the faulty component and replacing parts by trial and error. After the repair we clear the error and check that it does not come back. Find the nearest centre or contact us.
Want an accurate diagnosis? Book a diagnosis at the nearest MasterTuning centre.
Frequently asked questions
Does P0420 mean the catalytic converter must be changed?
Not always: it can be the rear lambda sensor, exhaust leaks or a rich mixture. They must be ruled out before replacing.
Can I drive with a clogged catalytic converter?
Better to avoid it: high back-pressure strains the engine and can damage valves and turbo.
How long does a catalytic converter last?
If the engine is in order it can exceed 200,000 km; rich mixture and oil consumption shorten its life a lot.
How is a clogged converter measured?
With exhaust back-pressure measurement compared with the engine’s expected values, plus a comparison of the two lambda signals.
