Thread: Pontiac GP 08 - P0300 & P0420

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  1. #1 Pontiac GP 08 - P0300 & P0420 
    SE Level Member sn95gt50's Avatar
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    I have a 2008 Base GP, 3800 engine, about 110,000 miles, daughters car.

    A couple of weeks ago she got CEL pulled the code P0420 Catalytic converter, cleared the code, car seams to be running fine, I don't drive it much.

    Today she got a flashing CEL and complained about no power and a lot of vibration. Pulled the code, P0300.

    I don't have my live data scanner, trying to get a hold of my buddy to get it back. What are the steps to get this diagnosed?

    Thanks,
    John
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  2. #2 Re: Pontiac GP 08 - P0300 & P0420 
    SE Level Member sn95gt50's Avatar
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    Forgot to mention, after clearing the P0420, it came back after a few days, prior to getting the P0300.
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  3. #3 Re: Pontiac GP 08 - P0300 & P0420 
    Killa Bee Scottydoggs's Avatar
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    if its a na engine the cat is likely clogged up.

    when its clogged it can cause the misfire code and the flashing cel.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  4. #4 Re: Pontiac GP 08 - P0300 & P0420 
    SE Level Member sn95gt50's Avatar
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    Just started it, about 30 degrees outside, initially idled around 1500, then calmed down to about 900. Listened for for vacuum leak didn't hear anything. Tried revving the engine and it goes to 3500 RPM in Park and won't go any further.

    Is that due to the cat clogged?

    Thanks for your help.
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  5. #5 Re: Pontiac GP 08 - P0300 & P0420 
    Killa Bee Scottydoggs's Avatar
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    there is a rev limiter in park and N, set around 3500, 4000 depending on year. so if it did the ricer bap bap bap sound thats the limiter.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  6. #6 Re: Pontiac GP 08 - P0300 & P0420 
    Donating Users bandook's Avatar
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    Wait, that's not 2 step?
    Top Swapped 01 Imp
    VS (very small?) cam, SD Headers, 2.8" pulley, 29°, ported everything, E85, AEM water/meth, Deka 60's, HPT tuned
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  8. #7 Re: Pontiac GP 08 - P0300 & P0420 
    Killa Bee Scottydoggs's Avatar
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    Quote Originally Posted by bandook View Post
    Wait, that's not 2 step?
    well i suppose that all depends on who you really are inside lol

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  9. #8 Re: Pontiac GP 08 - P0300 & P0420 
    GT Level Member mguzzo's Avatar
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    my vote is clogged cat.
    --
    "Silver Bullet" 98 GTP Coupe: Stock, rust free, and broadsided.
    Old '98 GTP Coupe: VS Cam, 3.0, S2IC, 42.5#, TOGs, N*/LQ4, Corsa. it once ran a 13 flat
    Older '98 GTP Sedan: Pullied, rockered, SSIC, etc. Stock 14.33 @ 96.5 / PB: 13.89 @ 101
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  10. #9 Re: Pontiac GP 08 - P0300 & P0420 
    Turbo is the way to go. Fivefingerdeathpunch's Avatar
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    I'd still change the spark plugs if they are original too.

    SMGPFC Member #1
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  11. #10 Re: Pontiac GP 08 - P0300 & P0420 
    SE Level Member sn95gt50's Avatar
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    Figured it was the cats as well, took it to a place called Iowa Muffler and Brake in Des Moines, they have always been straight with me (or so I think). He said the cats could be bad, but recommended fixing the misfire first, they recommended a small shop in the area, initially they thought it was a coil and stuck in a coil they knew was good, no go. They then determined it was the ICM that was bad, paid for the diag and headed to NAPA and picked up a new ICM, took a few minutes to install, fired it up and it instantly stalled, tried to start again it cranked longer than usual then fired up. Took it for a test drive and she drove great, neither P0300 or P0420 reappeared, I wouldn't be surprised if the P0420 reappeared.

    Question for you guys, how often do the ICMs fail? The original failed and Pontiac replaced $1000, then it failed again, local shop replaced it $600, now it failed again. This one cost me $220, the top of the line one that NAPA had Delphi.

    Thanks,
    John
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  12. #11 Re: Pontiac GP 08 - P0300 & P0420 
    SE Level Member sn95gt50's Avatar
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    Plugs were not original, maybe 30k on them.
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  13. #12 Re: Pontiac GP 08 - P0300 & P0420 
    Killa Bee Scottydoggs's Avatar
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    odd a mis fire could cause a cat code, the other way round, all the time....

    buy a used icm next time. people sell them for 20-30 bucks used. i have a spare one i picked up just to have.

    lets hope the cat code stays off so your not any deeper on this one.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  14. #13 Re: Pontiac GP 08 - P0300 & P0420 
    Donating Users bandook's Avatar
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    I have heard of misfires causing cat codes. You have so much unburnt fuel in the system it triggers sensor 2. I've heard of folks dropping a few dimes on a new cat, then the misfire continues and cooks the new converter. I've heard enough times about icms going bad that I grabbed one at the salvage yard just in case mine ever does. I'd rather go through a couple used ones then spend hundreds on a new one. Seems they can go out at 60k miles,.or 200k+.

    Are you.using stock coils?
    Top Swapped 01 Imp
    VS (very small?) cam, SD Headers, 2.8" pulley, 29°, ported everything, E85, AEM water/meth, Deka 60's, HPT tuned
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  15. #14 Re: Pontiac GP 08 - P0300 & P0420 
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    Yes ICM’s go bad and cause lots of weird things.

    I was thinking coil or ICM. 110 k is pretty low miles for a cat to go. Most all of mine have went 200-300K.


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  16. #15 Re: Pontiac GP 08 - P0300 & P0420 
    GrandPrix Junkie
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    ICM's can also fail due to a cracked coil. Had that happen on my 00 GT. JY ICM and coils and it fired right up and has been running fine ever since. Have about 200K on those parts now.
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  17. #16 Re: Pontiac GP 08 - P0300 & P0420 
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    Amazon sells a new AC delco ICM for $159


    ACDelco D1977A GM Original Equipment Ignition Coil Interface Module https://www.amazon.com/dp/B0013G0IDY..._cdIpEb9349G0P




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  18. #17 Re: Pontiac GP 08 - P0300 & P0420 
    SE Level Member sn95gt50's Avatar
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    Spent the weekend working on Jeeps with little to no internet access. Needed to have it going before I went to the guys weekend and didn't have time to wait for Amazon or Rock Auto to deliver. Good idea, about picking up a spare and a couple coils from the bone yard, may do that on my next trip.

    The misfire is still gone, but, the P0420 has returned, Probably need to think about replacing the cat. Not in a big hurry, could be the car has been missing for a while, just not as bad, may attribute to a premature cat failure.

    I see Rock Auto has several bolt in cats for around $200, what is the chance of those actually unbolting with out breaking the bolts off? A lot of rust in Iowa.

    I bought this car in 2008, same day GM announced Pontiac was shutting down, overall been a pretty good car. My kids have driven it for the last 6 or 7 years , a lot of short trips to and from school. That may attribute to the cats going bad so soon.

    Thanks for everyone's input, always appreciated!

    John
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