cat efficiency light...87xxx miles, CEL came on

reset the ECU by disconnecting the battery for a few mins, and was fine for a good 1100 miles, and the CEL lit up again.

from what i read, it could be bad sensors, a bad cat, or even a bad tank of gas? doubtful its the cat, doesnt have the bad cat conv smell, mileage is ok (23-ish, i sit thru LA traffic everyday).

i noticed it comes on after driving hwy speeds. first time it popped up was around 70mph..2nd time around was about 15 mins after i got off the hwy.


irrelevant, but i think the car might be burning oil too...4k miles since my last change, and while i was waiting for ECU to reset earlier today (did it again to rid of the CEL) i was snooping around n checked oil levels...its right in between the L and F lines.


any inputs appreciated.

 

do you have a header?

and a bad cat wouldnt effect your cas mileage.

and tC's are known to burn a little oil. Nothing unusual about where your level is. Add some oil if you want or better yet just change the oil all together. I usually change every 3 or 3.5 K.


If you dont have a header then I would actually guess that your cat has gone bad.

 

do you use those fuel system cleaners? if so, how often?

 

your primary O2 is on ur headers cat converter. if something is wrong with your cat, your CEL will pop up and give you that code... also if your sensor is bad it'll give you that code as well... i would start off by seeing if u could borrow an O2 from someone

 

the primary 02 comes before the cat on the headers as its main job is check the the AFRs during closed loop and make fuel trims accordingly.

A cat inefficiency code is a result of the secondary 02 sensor on the S-pipe either seeing that the cat has indeed gone bad or that the secondary sensor itself has gone bad

 

only thing im running is a CAI and trd axleback. stock header.

after i reset the ECU the frist time around, i threw in some lucas injector cleaner, at the time my mileage was goin down. i figured it was the winter grade gas, or dirty injectors, but it whatever it was, it went away. nevertheless, that was 1100miles ago.

 

see if you can borrow someone's secondary 02 sensor (the one on the S-pipe)

My guess is still that your cat has gone out :-(

 

Unplug the factory ECU harness from the ECU and replug it back in, everytime I have a CEL I have done this and it has always went away.

 

ignoring the problem and not finding out the cause for it is NEVER the proper way to do things....

 

I'm not saying to ignore the problem, but often times when you mess with the exhaust or the CAI you throw a CEL. I doubt the car's going to blow up, lol and I was just telling him how to get ride of it.

 

the P0420 code is usually a bad CAT. It can be an o2 sensor, but don't count on it. It won't hurt to try swapping it for a known good one, but you are most likely looking at a CAT replacement.