What usually causes it
- A worn out catalytic converter
- A failing rear oxygen sensor (sensor 2)
- An exhaust leak near the sensors
- A misfire, or oil or coolant burning in the engine, that damaged the converter
P0420Starts at: OK to drive, fix when convenient
Catalytic converter is not cleaning well enough (bank 1)
The catalytic converter is the part in the exhaust that cleans the fumes. It is not working as well as the computer expects, on the side of the engine with cylinder 1.
Check this first
Listen for ticking or hissing from the exhaust, which points to a leak. Ask a shop to check the front and rear oxygen sensor readings before you buy a new converter.
What to watch for
- A rotten egg smell from the exhaust
- The car feels choked or slow on hills
- A flashing check engine light. This means a misfire that can ruin the converter, so stop driving as soon as you safely can
Can I keep driving?
We rate P0420 as OK to drive, fix when convenient, as a starting point. Keep an eye on the signs below. If the light starts flashing, stop driving soon.
Quick answers about P0420
What does P0420 mean?
Catalytic converter is not cleaning well enough (bank 1). The catalytic converter is the part in the exhaust that cleans the fumes. It is not working as well as the computer expects, on the side of the engine with cylinder 1.
Can I keep driving with P0420?
We rate P0420 as OK to drive, fix when convenient, as a starting point. Keep an eye on the signs below. If the light starts flashing, stop driving soon.
What usually causes P0420?
The most common causes, in order: A worn out catalytic converter; A failing rear oxygen sensor (sensor 2); An exhaust leak near the sensors; A misfire, or oil or coolant burning in the engine, that damaged the converter.
Estimates only. A mechanic should confirm. The same code can mean slightly different things on different cars; the app explains it for your exact year, make, model and mileage.