P0420 code on 2008 Prix

Beware of aftermarket cats. Alot of em, especially the cheapos wont work for very long and you'll find yourself back at square one. They cant handle the volume. The OEM's are the best. Or look into a quality one made by Walker,Magnaflow,etc. Best to change both O2's when replacing the cat. They do wear out. HTH

He used a magnaflow

get the zzp downpipe and high flow cat with the corrected o2 for 2006 and up and be done with it. and or see if they can get a pcm programmed for you to eliminate this.

I tried calling them but they are closed, I'll give them a try in the morning. I don't fully understand their options. Can you tell me what the "corrected O2" for 2006 & up is about?

The 06 up models have had issues with any aftermarket cat system, they are very sensitive to the 02 placement/readings. My understanding is that ZZP adjusted the 02 placement to correct this.

FWI - e-mail is the fastest way to reach them. they take forever to reply to the voice mail.

Well here we are, almost 3 months to the day since I started this thread, and I still have P0420. The Magnaflow 49227, a cali cat for my car, hasn't turned it off. Nor has two new O2 sensors. I took the car to a local shop, they found nothing wrong. They told me I needed a GM cat. I called Magnaflow, they told me something must be wrong in the engine, and I need to have a five gas analyzer (tailpipe) test done. After much searching, I found a place in New Jersey to do it.

The car passed with flying colors. The guy said "this car is so clean, if you wanna kill yourself with it you better have a full tank of gas." He also said "I've seen this before...you need a GM cat."

I just emailed the place where I bought the Magnaflow, sent them all the paperwork, and told them I want to return it for a refund. If they don't cooperate, I'll take it up with my credit card co.

A GM cat will run me $750 to my door. Yeah, that hurts. If anyone else has any ideas I'd love to hear them. But the story I'm getting from both shops is that some cars simply don't do well with aftermarket cats, and Pontiac GPs are one of them.

Go to GM Parts Direct and check their prices. If you can get by with the federal cat then the price is much less than you stated. The California cat is much more expensive.

here this guy does custom pcm programming for the 2006 model. you just have to ask him what you want programmed out in the pcm and he should be able to do it. e-mail him for more information (Will). only other option is to use the gm model. personally I would just reprogram the pcm and be done with it.

http://www.getoverkilled.ca/3800sc.html

Thanks guys.

Well, after 3-1/2 months, 10,000 miles, and endless frustration, IT'S FIXED!!!!!!!!!!

I installed a genuine GM Cali catalytic converter a few days ago, and today the catalyst monitor program in the ECM ran and completed successfully for the first time since last December. WHEW.

So, lesson to all - no aftermarket cats in the PRIX!!

Thank you everyone for your suggestions and putting up with me!

So, lesson to all - no aftermarket cats in the PRIX!!



Glad you got the issue fixed!!!!

BTW....After market cats are fine for all but the 06 up years. the 06 has to have the o2 placement altered or pcm reprogrammed to run correctly.