catalytic converter CEL, how to replace catalytic converter

**scha0786** · 12-31-2011

Hello,

this is my first post to this site so be gentle. This is not even my car but my girlfriends car, you know not mine but responsible to change oil, fix and pay for everything basically. Anywho long story short.

A ways back the CEL came on and she brought it to her brother who is an auto mechanic, he pulled the code and it was a shot catalytic converter. So instead of installing the OEM cat he opted for the cheaper high flow. He didn't use any gaskets either, high temp sealant. So now a couple of months down the road the CEL came back on and I scanned with my edge insight and the code was catalytic related, something about difference between O2 sensors. Her brother claims that she isn't driving it hard enough and blah blah. I was getting sick of him giving me the run around. So I brought it to another friend or works at a GM dealer and he hooked it up to the computer and basically said that the high flow cat is tripping the CEL, basically replace with OEM if you want the light to stay off.

So I would like to know how hard this is to replace with no lift? Is there a how to with some pics somewhere on this site?

I am in alaska at the moment so I can't pull the CEL code at the moment.

**blueguy** · 12-31-2011

Here is the deal brutha...

The car's PCM is programmed to read off of the flow of the factory converter...IF there isn't a converter present...or even one that flows better than the factory unit, such as the cheaper HFC the guy installed (which is probably better than stock since they have a high fail rate for clogging anyways) then EVEN IF the cat is good, it'll still trip an SES light. Plenty of people on here and other forums have had great luck with ZZPerformance's 2.5" or 3" full bolt-in catted downpipes (whatever fits your budget...both catted DP's are better than stock for sure)...it can be done with simple hand tools and a jack/jack stands. No one seems to get SES lights from those either...and not only will you not see an SES from it, it'll get rid of the AWFUL factory downpipe/u-bend section in the exhaust...but you'll see a decent performance gain from it along with better MPG's to boot. So, it'll pay for itself I'm sure. You can snag them up in the For Sale section here...or get one new from ZZPerformance here: ZZPerformance - ZZP Downpipes #

Hope this helps.

**TheManInBlack** · 12-31-2011

I don't mean to just jump in but it's kind of on topic. I'm still new with exhaust, what is catback exhaust and downpipes, and u-bend deletes? Or maybe theres a different forum on this someone can suggest?
I have a 04 GP GTP and want to get started on modding it..

**scha0786** · 12-31-2011

nice thanks. ill give them a call.

**scha0786** · 12-31-2011

can i just install this to eliminate the p0420 code?

O2 Simulator Mini Cat Cel Fix

thanks

**sk8erdude** · 01-01-2012

i just installed the mini cat yesterday. ill keep ya posted on how well it works...

**scha0786** · 01-01-2012

this looks better in my mind, what ya think?

Rear O2 Emulator: 3800 Performance

**scha0786** · 01-04-2012

ordered this o2 emulator last night.

ill order the zzzdownpipe (2.5" offroad) in the spring.

**BillBoost37** · 01-04-2012

Starting around 00 GM tightened their standards in the pcm for how much difference between the pre cat and post cat sensors will accept. Likely all manf'rs did. Anyhow there are a couple of aftermarket brands that aren't high flow and work as well as a factory cat. I've honestly had very little flow or clogging issues with stock cats in my vehicles.

Depending on the year a sim may be a bad thing to try. There is a thread or two around that has info about the richening of the fuel to run cat tests on the newer models, they no longer look for a simple emulator. They look for true readings.

**z3r0** · 01-04-2012

i have the zzp o2 emulator and it works excellently for me. as i have a 97 but more less need to figure out at what mileage the o2 sim went in to see when they die

**scha0786** · 01-05-2012

so the emulator was a bad purchase?

Not sure if I agree that the emulator richens because all the emulator is doing is sending back a signal greater than 4 volts which tricks the computer in thinking its with spec, therefore no CEL is thrown and the computer does not trim up or down on the fuel.

Please provide some reasoning behind this richening thought

thanks

**BillBoost37** · 01-05-2012

The emulator wouldn't be richening the fueling. A test would be.

Please read through this whole thread. It will explain what I was talking about.
http://www.grandprixforums.net/remov...know-7092.html

**scha0786** · 01-26-2012

O2 emulator installed for 4 days so far and no more CEL light! I think it was the fix

**rocknnachos** · 01-27-2012

An O2 emulator is never "the fix."

**blueguy** · 01-27-2012

Originally Posted by rocknnachos

An O2 emulator is never "the fix."

It is on '97-'00 cars.

It's the '01 cat diagnostics that kill it after those four years...

**Mater** · 01-27-2012

Originally Posted by BillBoost37

The emulator wouldn't be richening the fueling. A test would be.

Please read through this whole thread. It will explain what I was talking about.
http://www.grandprixforums.net/remov...know-7092.html

this i ended up swapping in a PCM from a 2000 into my 2001 GT

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