The catalytic converter prevents the toxic gases produced by combustion from passing straight into the air. It is a steel box fitted into the exhaust line, with an average life of around 80,000 kilometres.
Symptoms of a Blocked Catalytic Converter
- Loss of pulling power; the car no longer performs as it did
- Poor acceleration and throttle response
- At an advanced stage, refusing to rev
- Failing the emissions test
- Increased fuel consumption
- A rotten egg smell from the exhaust
- Rattling from the exhaust
A Catalyst Rarely Fails on Its Own
This is the key point: a catalytic converter usually blocks as the consequence of another fault. Incomplete combustion, oil burning or an ignition system problem fills it.
Which means cleaning or replacing it without finding the real cause is not a lasting fix; the new one reaches the same state quickly and the cost is repeated.
Is the Catalyst Really Finished?
You cannot tell by eye. Making that call requires assessing, with a tool:
- Catalyst efficiency fault codes and the conditions under which they set
- Live data from the front and rear lambda sensors — how they behave relative to each other shows whether the catalyst is working
- Freeze frame data — the conditions when the fault occurred
- The state of the ignition and fuel systems — is the cause still present
Replacing a catalyst without this assessment is expensive and the outcome is uncertain.
Cleaning Is Not Always the Answer
Cleaning only works where the blockage is deposit-related. If the internal honeycomb is physically broken, melted, or the coating is exhausted, cleaning achieves nothing and the part must be replaced.
Telling which situation you are in also comes down to measurement. Without that, money spent on cleaning is wasted.
Protecting the Catalyst
- Do not delay when the check engine light comes on; incomplete combustion fills the catalyst.
- Do not ignore oil consumption complaints.
- If you mostly do short journeys, take a longer run periodically.
- Keep to the service schedule.