Catalytic Converter
What it is
The catalytic converter is a canister in the exhaust system packed with a precious-metal honeycomb (platinum, palladium, rhodium). It is one of the most expensive emissions parts on the car — and a frequent theft target for its metals.
What it does
It chemically converts harmful exhaust gases — carbon monoxide, unburned hydrocarbons and nitrogen oxides — into far less harmful carbon dioxide, water and nitrogen. When its efficiency drops below a threshold, the downstream oxygen sensor notices and the computer sets a P0420/P0430 code.
Symptoms of failure
- P0420 or P0430 "catalyst efficiency below threshold" code
- Failed emissions test
- Sluggish acceleration or loss of power (if clogged)
- Rotten-egg / sulphur smell
- Rattling noise from under the car (broken internal honeycomb)
Common fault codes
Which vehicles need it
All petrol vehicles; high-mileage cars and those that have run rich or misfired for a long time are most affected.
Replacement cost
| DIY (part only) | $150–$600 |
|---|---|
| At a shop (parts + labor) | $900–$2,500 |
| Replacement interval | Designed to last the life of the car (100,000+ miles). Premature failure usually means an upstream problem — fix the root cause first. |
| DIY difficulty | Hard / Professional — exhaust work, often welded; bolt-on units are DIY-able with care |
| Recommended brands | Walker, MagnaFlow, Eastern Catalytic, OEM |
Where to buy the part
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Frequently asked questions
Will a cat cleaner fix a P0420?
Sometimes, if the converter is only mildly contaminated and the real problem (a small oil/coolant burn or rich condition) is fixed. A cleaner cannot rebuild a converter that has physically failed, but it is a cheap first try before replacement.
Can I just replace the oxygen sensor instead of the converter?
Only if the sensor is the actual fault. On a genuine P0420 the converter is worn about 55% of the time and the rear O2 sensor about 30% — diagnose before spending on the expensive part.
Why is my catalytic converter so expensive?
It contains platinum, palladium and rhodium — among the most valuable metals on earth. That cost (and theft risk) is why it is one of the priciest single parts to replace.