P0433 — Main Catalyst Efficiency Below Threshold (Bank 2)
Drive with caution — fix soon.
What P0433 means
This code means the main catalytic converter on bank 2 has fallen below its expected efficiency, so it isn't reducing emissions as it should. It's most often caused by a worn converter, but a faulty oxygen sensor, an exhaust leak, or an underlying misfire can also set it. Diagnosis typically inspects the sensors, exhaust, and engine condition before concluding the converter must be replaced.
Common symptoms
- Check engine light is on
- Failed emissions or smog test
- Reduced fuel economy
- Slight loss of power or sluggish acceleration
- Sulfur or rotten-egg smell from the exhaust
Common causes
- Worn or failing main catalytic converter on bank 2
- Faulty downstream oxygen (O2) sensor
- Exhaust leak near the converter or sensors
- Engine misfire damaging the catalyst
- Rich fuel mixture overloading the converter
Typical repair cost
$200 – $2200
Varies by vehicle and root cause.
Frequently asked questions
Can I keep driving with a P0433 code?
Usually yes for the short term, since the car typically runs fine. But the main converter isn't cleaning the exhaust well, so emissions rise and you may fail a smog test. Have it diagnosed within a week or two, especially if a misfire is contributing.
How much does it cost to fix a P0433?
An oxygen sensor or exhaust leak often costs $200 to $500 to fix. If the main catalytic converter on bank 2 needs replacing, the bill can run roughly $900 to $2,200 depending on the vehicle.
Is a P0433 code serious?
It's a moderate concern. It won't usually strand you, but a degraded main catalyst means more pollution and can worsen if a misfire or rich mixture is left unfixed. Address it before it leads to a costly converter replacement.
What's the difference between the main and warm-up catalyst codes?
The main catalyst (P0433) is the larger converter farther from the engine that does most of the emissions cleaning, while the warm-up catalyst (P0432) is the smaller one closer to the engine. Both being on bank 2 means they're on the same cylinder bank.