What does code P0420 mean?
P0420 means Bank 1's catalytic converter is not cleaning the exhaust well enough. The computer compares the O2 sensors before and after the converter. When their readings look alike, it concludes the converter has become weak.
Why does code P0420 appear?
- The catalytic converter is old or damaged.
- An exhaust leak near the O2 sensors.
- The O2 sensor after the converter is reading wrong.
- Misfires or the engine burning oil have damaged the converter.
What can you safely check for P0420?
- Write down every code the scanner shows, not just this one. Do it before clearing them, because the other codes help the mechanic find the real cause faster.
- With the engine running, listen for a puffing exhaust-leak sound from under the car. Don't touch the hot exhaust.
- Note whether the exhaust smells like rotten eggs, or whether something rattles underneath.
Is it safe to drive with P0420?
If the car has normal power and there are no other codes, you can usually drive for a few days, but do get it checked. If power drops a lot, there is a burning smell from underneath or the engine runs hot, stop: a blocked converter can choke the engine.
Safety: never remove the radiator cap on a hot engine; boiling coolant can burn you. Keep your hands away from the fan and belts while the engine runs. If you smell fuel, switch off, keep any flame or cigarette away and call a mechanic.
When should you call a mechanic?
A catalytic converter is expensive, so first have a car mechanic (mistri) check for exhaust leaks and test the O2 sensors. If there are misfire or other codes too, fix those first, or a new converter can be ruined as well.