Xanadu

My check engine light came on and I went to Auto Zone for them to check what the code was and it came out as P0420. It says that the catalyst system efficiency for bank 1 is below threshold. The guy at Auto Zone said that it might be oxygen (02) sensors. He also told me to go to a mechanic and for them to look at it first before I do anything. What should I do? Anyone that has had this code come up what have you done? I hope it's just my O2 sensors.

If I don't get this replaced what would happen? Would my car pass the state inspection or would it not pass because of high/low emissions caused by this code?

butters

need more info on what year and car you have. Also search for info on cel codes here on h-t. of course you will not pass any smog test with a cel. A smog tech can also see if you had cels prior to getting it fixed. Your best bet is to scan the code, make sure you know what code it is referring too and get it fixed. if its just an o2 sensor, then thats easy to replace. good luck

btw, when my obd2 civic threw a code for o2 sensor, i'm positive the code was a two digit code like 62 or something.

93Civac

Found this somewhere. Hope it helps

Each time you start the engine to your vehicle the computer runs
tests of the catalytic converter. If the converter fails the test the computer turns on the service engine soon light and will report the diagnostic code P0420. What this all means is the converter is not working right. A replacement converter may be needed but I would suggest a few diagnostic checks first. The vehicles computer uses information from 2 different oxygen sensors to compare the oxygen entering the converter to the oxygen exiting the converter. The sensor at the exit of the converter will read a different value than the sensor at the front of the converter. Thats because the converter uses up oxygen in the final phase of operation. If a sensor is not reporting to the computer correctly (lying) the computer could falsely fail the converter. Also, be aware that the exhaust cannot have any leaks. Exhaust leaks near the oxygen sensors can and will cause false readings. One last note, if your converter has failed check with your dealer. There is a time and mileage warranty on the converter and your vehicle maybe covered. Most of the time, all the dealer will need is your vehicle identification number and the mileage when you call to answer that question.

Xanadu

I have a 1999 Civic LX with about 101,000 miles. When it was below 100,000 miles my check engine light came on but it was under warranty. I took it to the dealer and they got it all fixed. I don't remember what they replaced. Now it's not under warranty. Where should I go before I go to the dealer?

Xanadu

Bump