I have the CEL light come on on my 2000 Corolla. I have only 138000 miles on it. I am wondering if it is really the CAT. I already did a tune up, put new Iridium sparks worth $ 170 from dealer, changed air filter but no avail. I had already replaced the O2 sensors ( both) only 5 years ago and have put about 90000 miles since.I got an estimate for a new Catalytic converter for $ 1580. I am wondering if I should put an after market and would it work as good? My car is running great for now.
Please help!
-S
Answer
The PCM copares switch rates between the front O2 sensors and the downstream catalyst monitors. The catylist monitors are often mistaken as O2 sensors, and they are, but that is not their job, or what they are called. By comparing the switch rates between the front (before cat) and rear (downstream of cat) the PCM knows if the cat is affecting the exaust, and how much it is affecting the exaust. If it sees little or no effect o the exaust gases that have passed through the cat, then it decides that the cat is not working anymore, ad sets a P0420, or a P0430, depending on which bank it is. To check this yourself, you will need to bring up data stream on your scanner, watch the upstream and downstream O2 parameters and see if they are following each other closely. If the cat is working right, you should see a fairly rapid switch rate, probably 5 or 6 times a minute on the front O2, but almost a flat line just above .5 volts on the rear. If the rear is switching often you probably need a catalytic converter.
you need someone with an obd 2 scan tool.
It could be either the Sensors or the cat. An aftermarket cat is more like $369 plus $100 labor. do not believe the Toyota scam of the $1000 cat . They have been overcharging people off for years on this one.
