Thread: Check Engine Light: P0128 Code

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  1. #1 Check Engine Light: P0128 Code 
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    I have a 2005 GP. Recently, the check engine light came on. I had it scanned, and it showed P0128: coolant temp below regulated temp. I do remember that it came on during a cool morning (45F). Is it possible the code will reset, now that temps are warmer ? Is there a certain number of engine starts that will clear it ?

    Is there a way to clear the codes quicker, so I can see if it comes back ?

    And lastly, is there a way to retrieve trouble codes similar to the way that older OBD-1 cars could ? You woul jumper the diagnostic terminal and count flashing lights for the number of the code.
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  2. #2 Re: Check Engine Light: P0128 Code 
    Killa Bee Scottydoggs's Avatar
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    temp sensor is under the t stat housing, bottom of the lim, just change it. look over the wires first tho, they could be bad.

    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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  3. #3 Re: Check Engine Light: P0128 Code 
    I live here. 02NavyBlue's Avatar
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    I believe that code will reset, I had it on an impala with the 3.8 and it was stored as previous codes, but not a current code.
    Use an OBD II scan tool to retrieve codes. They run as low as $50 to get a simple code reader, but you can go to an auto parts store and they will read codes for free.
    No jumper wire techniques on OBD II, just a scan tool.

    I fixed this issue by putting in a new thermostat (Also did a cooling system flush and new rad cap, the t-stat is what fixed the problem)
    2006 Grand Prix GT S/C 109k - Modded Transgo Shift Kit, Gutted Airbox, Dash Cam, and Inlays. Retros soon to come.
    2002 Grand Prix GT N/A 127k - Same as 06 Plus: Trans Cooler, DIY Aux Input, LED lighting, Suspension Upgrades, Tint, Retrofits.
    Sold.
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  4. #4 Re: Check Engine Light: P0128 Code 
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    Quote Originally Posted by Scottydoggs View Post
    temp sensor is under the t stat housing, bottom of the lim, just change it. look over the wires first tho, they could be bad.
    Hey Scotty u've helped me on the trans forum and now I have a new problem. P0128 code just came on. From what I hear its a bad thermostat? If so what brand/temp do I swap it with? Autozone says a 195 degree duralast? Is that correct?
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  5. #5 Re: Check Engine Light: P0128 Code 
    Killa Bee Scottydoggs's Avatar
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    OBD-II Trouble Code: P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) looks like a temp sensor.

    if your gonna change the t stat get a 195. i have no fav brand.

    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: Check Engine Light: P0128 Code 
    I live here. 02NavyBlue's Avatar
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    All it's saying is it's detecting that the system took too long to warm up. "The intent of the P0128 code is to indicate a faulty thermostat."

    Quote Originally Posted by kingspadeshan View Post
    Hey Scotty u've helped me on the trans forum and now I have a new problem. P0128 code just came on. From what I hear its a bad thermostat? If so what brand/temp do I swap it with? Autozone says a 195 degree duralast? Is that correct?
    Stant is a very common brand for thermostats, if you go with them get their superstat version. It's a few bucks more but is identical to oem.
    2006 Grand Prix GT S/C 109k - Modded Transgo Shift Kit, Gutted Airbox, Dash Cam, and Inlays. Retros soon to come.
    2002 Grand Prix GT N/A 127k - Same as 06 Plus: Trans Cooler, DIY Aux Input, LED lighting, Suspension Upgrades, Tint, Retrofits.
    Sold.
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  7. #7 Re: Check Engine Light: P0128 Code 
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    Thanks Blue
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  8. #8 Re: Check Engine Light: P0128 Code 
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    Quote Originally Posted by 02NavyBlue View Post
    All it's saying is it's detecting that the system took too long to warm up. "The intent of the P0128 code is to indicate a faulty thermostat."



    Stant is a very common brand for thermostats, if you go with them get their superstat version. It's a few bucks more but is identical to oem.
    Is it safe to drive the car for a day or two without damaging anything ?
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  9. #9 Re: Check Engine Light: P0128 Code 
    I live here. 02NavyBlue's Avatar
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    With a defective t-stat? Yes it will be fine.
    2006 Grand Prix GT S/C 109k - Modded Transgo Shift Kit, Gutted Airbox, Dash Cam, and Inlays. Retros soon to come.
    2002 Grand Prix GT N/A 127k - Same as 06 Plus: Trans Cooler, DIY Aux Input, LED lighting, Suspension Upgrades, Tint, Retrofits.
    Sold.
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  10. #10 Re: Check Engine Light: P0128 Code 
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    Oh ok good, I'm in So Cal and will driving it to work and then straight to the dealer right after work. Only had the car a week.
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  11. #11 Re: Check Engine Light: P0128 Code 
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    FYI my thermostat was stuck wide open. Replaced it and no more cel or codes. Woo hoo
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  12. #12 Re: Check Engine Light: P0128 Code 
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    Yeah that's what happens, it's nice GM used a code for that. Thanks for the update.
    2006 Grand Prix GT S/C 109k - Modded Transgo Shift Kit, Gutted Airbox, Dash Cam, and Inlays. Retros soon to come.
    2002 Grand Prix GT N/A 127k - Same as 06 Plus: Trans Cooler, DIY Aux Input, LED lighting, Suspension Upgrades, Tint, Retrofits.
    Sold.
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