A failing catalytic converter can fail a smog check, but it is often a symptom rather than the root problem. Misfires and rich mixtures destroy converters. Confirm the cause before you replace one.
Key takeaways
- Converters wear out because of other faults.
- P0420 does not guarantee a bad converter.
- Fix the cause first.
What a converter does
It converts harmful exhaust gases into less harmful ones using a heated catalyst. It must reach temperature to work.
Signs of failure
A rotten egg smell, reduced power, a rattle from inside, a lit light and a high emissions result all point toward the converter.
Causes
Misfires, oil burning, coolant leaks and fuel mixture problems poison the catalyst. Replacing a converter without fixing the cause damages the new one.
Testing
We check back pressure, temperature across the converter and oxygen sensor readings before recommending replacement.
Replacement
California has rules about which converters are legal. Ask about a part that matches your car's certification.
How long a converter should last
A catalytic converter can last the life of a car when the engine runs cleanly. It fails early when misfires dump raw fuel into it, when oil or coolant burns in the engine or when it is physically damaged. If your converter failed at low mileage, the root cause matters more than the part. Replacing the converter without fixing the cause means paying for another one soon.
California rules on replacement converters
California has specific requirements for replacement catalytic converters, and many aftermarket converters sold for other states are not legal here. Ask your shop which converter is approved for your vehicle and keep the paperwork. Installing a non-approved converter can cause a failed test and a repeat repair. Because the part is expensive, confirm the diagnosis, the legal part and the warranty before you authorize the work.
Need help in south Bakersfield?
Questions about smog repair? Read our Smog Repair page, call (661) 599-9098 or request a time. Peña's Auto Electric, Smog & Repair, 303 Taft Hwy, Suite B, Bakersfield, CA 93307. Mon to Fri 9:30 AM to 5:30 PM, Sat 8 AM to 1 PM.
Frequently asked questions
Does P0420 mean replace the converter?
Not always.
What destroys a converter?
Misfires, oil and coolant leaks.
Can a converter be cleaned?
Usually not reliably.
Are all aftermarket converters legal?
No. Ask about California-approved parts.
Related reading
Sources
- California Bureau of Automotive Repair, Smog Check program and consumer information