Thread: p0420

I had a p0420 a few months back. I had the car for about 10k miles before it started to happen. I dont notice any loss in performance, maybe some in fuel economy. The cat on there was a universal magnaflow welded on, it seemed to have been falilng apart causing substrate to go in the o2 sensor. I replaced the cat with a magnaflow direct fit and the code is still there. could it be the o2 sensor is actually bad or what?

Thanks

That code is taking the expected difference between the two O2 sensors and comparing that to an expected value. Meanwhile the sensors are also monitored for heating up quickly and reading etc. Typically the pcm would throw a code for one of them if it were a sensor.

I have seen in a lot of cases where magnaflow replacements didn't meet the requirements of the pcm.

You need to clear the code after cat replacement and see if it comes back.

I believe they cleared the code but it came on a lot faster than it used to. I only had to drive like 10 miles this time rather than 50. maybe they didnt clear the codes?? It was either get the magnaflow replacement or go to the dealer and spend $1100

Which is why the dealer one doesn't set a code. Lemme dig something up that'll be cheap and should help you

Fifth post down explains it and says it all.

http://www.grandprixforums.net/persi...mad-70364.html

I mean if I have to I can get a tuning cable and block the code. Cause I have a feeling it's why i get below 20mpg avg
This is really aggravating me. I hope after I install the new o2 sensor that it'll just go away but im not sure. the shop isnt liable for the light being back on because I had to bring my own part, not paying 1100 for a new cat from the dealer, better off dumping the car into a pole or ditch. I just paid 300 for the direct fit cat.

Looked at post #16 on that link? The mod doesnt always work. and i cant afford to be 'trying' stuff anymore lol.

No worries, I tried to give you more info and suggest a $5 fix. Tell you what, send me your paypal address. I'll send you $10 to buy defoulers and try it out. Do that instead of putting a new sensor in. If that works, send me back the $10. If not, keep the defoulers and buy the more expensive sensor.

Right...I'm willing to give you the chance to try it free.

There are plenty of other options besides the dealer cat.

I am pretty sure magnaflow sells a high end cat converter for 250-350 bucks, I forget the part number but I know matt knows which cat I am talking about.

Originally Posted by Fivefingerdeathpunch

There are plenty of other options besides the dealer cat.

I am pretty sure magnaflow sells a high end cat converter for 250-350 bucks, I forget the part number but I know matt knows which cat I am talking about.

I bought their direct fit converter lol.

Originally Posted by BillBoost37

No worries, I tried to give you more info and suggest a $5 fix. Tell you what, send me your paypal address. I'll send you $10 to buy defoulers and try it out. Do that instead of putting a new sensor in. If that works, send me back the $10. If not, keep the defoulers and buy the more expensive sensor.

Right...I'm willing to give you the chance to try it free.

I already bought the o2 sensor a few days ago just havent been able to install it yet. The defouler requires a weld doesnt it?

Originally Posted by sirricealot

I mean if I have to I can get a tuning cable and block the code. Cause I have a feeling it's why i get below 20mpg avg
This is really aggravating me. I hope after I install the new o2 sensor that it'll just go away but im not sure. the shop isnt liable for the light being back on because I had to bring my own part, not paying 1100 for a new cat from the dealer, better off dumping the car into a pole or ditch. I just paid 300 for the direct fit cat.

There are so many people in Illinois with HP tuners just have it tuned out save a lot of money. And be done with it . No need in dealing with the spark plug fouler it didn't work for me either when I first got my Gxp. but if you want a factory cat and insist on it I still have mine. And BTW yes that is why you're getting ****ty mileage right now

well idk if theres anyone local to me that has HP tuners or not. I thought about buying it myself but im not sure exactly lol. I'd like to have it tuned though, just didnt wanna have to spend lots of $$.

You could nickel and dime yourself to the point where you wish you'd had a tune or buy HP tuners, diablo, trifecta etc....but I'd be willing to sell you my old cat I f you insist on having one it is factory btw and contrary to belief high flow cats are worth like 2hp or something small llikethat. So don't feed into it cats are very efficient from the factory.

Welll i got the magnaflow because it was either that, a universal, or dealership. I may just save up for a tune and do it myself...seems pretty easy. Im guessin hp tuners is the best?

Just do what Billboost said, hes always right. Or buy a quality Walker cat. High flow cats arnt worth it.

Originally Posted by sirricealot

I bought their direct fit converter lol.

Right, you bought the cheapest cat they make, which is why the SES is still on.

This applies to several threads, if people want to just throw money and not take our advise send me the money so I can go buy a case of new bowties if ya know what i mean.

Not to be harsh, but it is still freaking snowing wet heavy slushy crap south of the Twin Cites and it is April 18.

Originally Posted by sirricealot

Welll i got the magnaflow because it was either that, a universal, or dealership. I may just save up for a tune and do it myself...seems pretty easy. Im guessin hp tuners is the best?

I like HP tuners but efi live is out there That have the ability to turn off the code and test in the pcm. You can request the same from diablo and trifecta As well