Catalytic Converter Replacement at Johnny's Automotive
A P0420 code doesn't always mean the converter failed. We check the sensors, leaks and engine first, so you only replace the expensive part when it's the actual problem.
Do I really need a new catalytic converter?
The catalytic converter sits in the exhaust between the engine and the muffler, and its job is chemistry. Hot exhaust passes through a ceramic honeycomb coated in precious metals, and that coating converts most of the harmful gas into carbon dioxide, nitrogen and water vapor. There are no moving parts inside it. It either works, or the honeycomb has been contaminated, melted, or broken apart.
Here's the part we'd rather tell you up front. The most common code people bring us, P0420, does not say the converter is bad. It says the downstream oxygen sensor is reading a signal too close to the upstream one. A lazy or failing sensor, an exhaust leak ahead of the sensor, a misfire, or oil and coolant getting burned in the engine will all set that code with a perfectly good converter bolted to the car. Replacing the converter without ruling those out is the most expensive way to guess wrong, because it's the priciest part of the exhaust by a wide margin.
So we work backwards. We look at live sensor data, check for leaks ahead of the sensor, read fuel trims and misfire counts, and figure out whether the engine has been feeding the converter something that killed it. A converter that failed because of a misfire or a leaking valve seal will fail again in short order if nobody fixes the cause. When it truly is the converter, we say so plainly and replace it.
Theft is the other reason people call us about converters. Thieves cut them out for the metal inside, and you'll know the moment you turn the key, because the car roars. We can replace the converter and, on the vehicles that get targeted most, add a shield or cable guard while it's already on the lift. Converter work we perform is covered by our 36 month, 36,000 mile nationwide warranty.
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Problems we fix
Our experts diagnose and resolve any issue.
A rotten egg or sulfur smell from the tailpipe
The converter isn't processing sulfur compounds the way it should, often because the honeycomb is contaminated or the engine is running rich. The smell is a symptom, not the diagnosis.
Check engine light with a P0420 code
That code compares two oxygen sensors, so it can come from a tired sensor, a leak ahead of it, or a misfire. The converter is one possible cause out of several.
The engine feels choked and won't pull
A converter with a collapsed or melted honeycomb restricts flow, so the engine can't breathe out. It usually feels worst at highway speed or climbing a grade.
A rattle like gravel in a can under the car
The ceramic substrate inside has broken up and the loose pieces are moving around. Once it's rattling, cleaning is off the table.
The car roared like a race car this morning
That's the sound of a converter cut out of the exhaust overnight. Theft is real here, and the fix is replacement plus a guard on the vehicles thieves keep coming back to.
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Learn moreCatalytic Converter Replacement questions, answered
Common questions about our catalytic converter replacement services.
How do you know it's the converter and not a sensor?
We watch what both oxygen sensors are actually doing while the engine runs, instead of trusting the code. A healthy converter makes the downstream sensor go relatively flat while the upstream one keeps switching. If that pattern is there, the converter is doing its job and we go looking somewhere else.
Can a converter be cleaned instead of replaced?
Occasionally. If the honeycomb is intact and just fouled from a condition we've since fixed, a cleaning is worth trying and we'll tell you the odds honestly. If it's rattling, melted, or plugged, no chemical or cleaning process is bringing it back and we won't take your money to try.
Why are catalytic converters so expensive?
The coating inside contains platinum, palladium and rhodium, and those metals are priced like the commodities they are. That's also exactly why they get stolen. It's the single most expensive component on most exhaust systems, which is the whole reason we diagnose carefully before condemning one.
What can I do about converter theft?
Some vehicles get targeted far more than others, usually the ones sitting high enough to slide under. For those we can install a shield or cable guard, and it's a lot cheaper when we do it during another repair while the car is already up. Parking where the underside isn't easy to reach helps too.
Will replacing the converter fix my failed emissions or turn off the light?
Only if the converter was the real cause. If a leak, a misfire, or an oil burning issue is what set the code, the light comes back on a new converter, sometimes within a week. That's why we chase the cause first and replace the part second.
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