Thread: Bad rear 02 sensor and random misfires. Can runs just fine.

sounds like your cat is clogged. thats what my car was doin. when you go wot your putting a lot of pressure on the exhaust, and if your cats clogged, the exhaust cant go anywhere, which will make your car misfire. and if the cat is clogged, the rear o2 cannot get a proper reading, which is why you have that code. my suggestion is order an off road 3" dp from zzp and put it on. all depends on if you need to pass emissions.

Clogged cat is the first thing I thought as well until I closely examined the auto zone printout. From what it says it seems to suggest that the heater circuit isn't working in the sensor, and that what causes the code. I was thinking that a seperate code would come up for a clogged cat. I could be totally off though... It's been known to happen.

Can anyone confirm which of these two that code represents?

Edit: Did you have the same two codes?

a clogged cat will come up and say catylist efficiency below threshold. but it can also bring up the code saying the rear 02 isnt functioning properly. its hit and miss. my moneys on the cat though.

Maybe I'll just remove it and punch it out with a crowbar or something. The car hit 200K yesterday, and I'll be getting rid of it in april, so I'm sure as hell not going to sink more money into it.

cat doesnt unbolt. its part of the dp

I was thinking unbolting the down pipe. But I just remembered that the ubend would be in the way. Damn.

in the way of what?

Of punching something through the rear of the cat... Isn't it right before the ubend?

It's been quite a while since I've been underneath a grand prix.

check out a picture of one in the for sale section. im not sure i never really looked at mine. i took it off and shipped it back to zzp for cat credit

That's what a stocker looks like. I was planning on hollowing it out from the rear, then I remembered that the ubend prevents me from doing so.

hmm yep...cut your cat out and have a pipe welded in

Originally Posted by Jakegday

you do realize this isnt gonna turn your SES light off, right?

Why not? My experience with this car is that after fixing the problem and starting the car a few times, the light always goes off. The code is still there. But the light is off.

The cat is not clogged. This was confirmed with a back pressure check.

what was the reading on the backpressure test?

reason i ask is i had the same code and the car ran fine...then a couple weeks later my cat became clogged and then it ran like crap, pieces of the cat actually damaged the rear 02 sensor putting a big dent in the cage around the sensor.

Sorry, but I have no idea. I took it to an exhaust shop where I had taken another car of mine before. I figure if they're going to turn me away and tell me that I don't need new stuff then they must really mean it

id try first by just taking out the rear 02 and doing a visual inspection on it