My wife and I have a 1997 Honda Accord, roughly 260k miles. A few months back the Check Engine light came on, diagnostic came back with P0420, typically indicating the catalytic converter is shot. Who am I to argue, it was an factory part. So we replaced that with an inexpensive Magnaflow converter. (don’t have the part number on me); this was 5 days ago. Today my wife takes the car in for inspection. Check Engine is still on with the same code. The guy at the testing station begins laughing at my wife when she says we only spent about 200 in parts and labour on the new converter. I’m inclined to think that since we already replaced the converter that I should be looking somewhere else (O2 sensor maybe). But I also don’t want to just start throwing parts at it. Do I have a case here? I would really prefer not to spend $1000 on a car that old with that many miles on it just to pass inspection. Thoughts?
A p0420 is very often the O2 sensor past the catalytic converter but, since yours is original, it could be the one before the converter as well. It could also be an exhaust leak.
When you get that code on a lower mileage car, it could be due to other problems but on a high mile car, one or both those sensors are usually bad.
Unless you have (or have access to) an OBD2 tool that allows you to read the data from those sensors, you may need to take it somewhere to see which sensor is bad or to see what else is wrong.
The sensors themselves may be around $250 or so. It is probably around an hour’s worth of labo for someone with a lift.
$200 for a new converter with installation is really cheap. The converter may not be a very good one. The good ones are made of platinum, a precious metal. That’s probably why he laughed because they tend to cost a lot more than that.
Disconnect your negative battery cable. Turn the headlights on and off. Reconnect the battery. The CEL should be off. If it stays off for a day or two, go have your car re-tested…The part that set the P0420 code is the rear oxygen sensor…I would replace that next…
I’ve seen some problems reported here prior associated w/inexpensive cats. I don’t know if this is the OP’er problem, but OP might want to plug his car into the website below and make sure he’s got the correct cat for his make/model.
Don’t fix anything else on your car, it has too many miles on it. A repair costs more than the car is now worth. You are into the money pit phase of a car’s life. There are other major parts that need changing, and they are expensive.