99,200 miles check engine light came on, Dealer said needs both cats replaced ($2600)! I bought new cats online for $380. I installed them and noticed that the cats are approved for CA ( i am in PA). Reconnected the battery and the light was no longer on!!! :) 25 miles later it came on again. I called the auto parts store (online) to tell them about the CA approved cats being an issue and they said they will work fine and that I probably never needed cats in the first place, and to replace the o2 sensors. I did not get the code read yet because I as I understand it it will simply say that there is an emission problem. How was the dealer positive I needed Cats replaced? What should I do now?

Thoughts?

First off, Cheap aftermarket cats are junk. I put one in my truck and is barely passed smog. Buy the next time I was up for smog check, it was not doing anything. I had to replace it with an OEM cat.

That said, the stock cat should last a good 200k unless something went wrong and hurt it. Your stock cat should be fine. However, OS sensors only last about 100k, so I am betting that is what has failed and your dealer is lying to you. Most ECUs will tell you what sensor has failed so get someone to read the code.

I just had the codes downloaded and this is what I found:

P1130
air/fuel sensor bank 1 sensor 1
Open or short circuit or poor connection

P1135
air/fuel sensor heater circuit response bank 1 sensor 1
Open or short circuit or poor connection

P0125
Coolant temp is low or bad sensor
engine took too long to warm up to operating temp.


Which sensor is bank 1 sensor 1? Before the cats I assume?
given these codes is there any reason to believe the new cats are not working? I will most likely put the old ones back one after I get through these other issues.

Thanks for your help.

Get the factory service manual. It will tell you what sensor is what. I don't have one for that year. It looks like the O2 sensor is bad or you have a loose connection. Check the wires to it. They are down low and can get packed with mud and water.

The low coolant temp should be a different issues. It could be the temp sensor. What does the gauge show? Does it come up to operating temp normally? It could be a bad thermostat. At neat 100k miles, you should have replaced the timing belt (assuming you have the V6) along with the water pump and thermostat.