2001 Celica with catalitic convertor code

I have a 2001 Celica and the check engine light is on and I had the code read and they said it was the cat. Is it really the cat or could it be something else like an O2 sensor.

What is the code? what number we dont like guessing and it does make a difference.

What code? It should be in the format “P1234” There are several codes that may be incorrectly interpreted as a converter problem. Get the code and post it back here. Many auto parts stores will read them for free.

BTW the number of miles on it and anything else going on that is not normal might help pin it down.

Yes, it could be a faulty O2 sensor. An O2 sensor can be checked. It only takes a proper mechanic, with the proper tool, to do so.
The catalytic converter and the O2 sensors are on the tail-end of everything, combustion-wise, which has taken place within the engine. If proper combustion hasn’t happened, the results can negatively affect the catalytic converter and the oxygen sensors. Your proper mechanic knows how to treat the engine so that the output (exhaust) will be as it should be.
If parts are just changed, the problems will still be there, and will adversely affect the new parts. True troubleshooting is needed, and as a customer, is what you deserve.

It is code P0420. The car has 132000 miles on it and as far as I know there are no other problems.

Ah, the dreaded P0420 code, catalytic converter low efficiency code. What the ECM is telling you is that it is seeing the upstream O2 sensor mirror the downstream O2 sensor. Either engine conditions are causing the sensors to indicate constantly rich or lean or the sensors are tracking each other indicating that the catalytic converter is not processing the gases efficiently.

Do as ‘hellokit’ suggests. Have a mechanic read the sensor responses and verify that the sensors will indeed cycle. Then, he should compare the upstream voltage to the downstream voltage to see if they are tracking. If all is in order a catalyic converter replacement might be the next step.

BTW which engine is in ?his car? If you know the engine model i.e. 2AZ-FE let us in on the secret.