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Thread: P0128 issue

  1. #1

    P0128 issue

    Having issues with p0128 setting on aunts 07 hhr. When code sets a/c is disabled. Once code is cleared a/c is allowed by pcm again. Problem is intermittent, thermostat was bad and was replaced with new part and that lasted 2 months. Code set again and thermostat was pulled back out for inspection and looks good. Wiring looks ok will ohm the wires tomorrow but since it's intermittent I'm guessing it will ck out good. My uncle said someone told him the ecm is bad. My question is can I disble that code and will a/c still work if the fault reoccurs
    Last edited by prostreet1967; 07-26-2015 at 07:14 PM.

  2. #2
    Advanced Tuner CatnipG5Bandit's Avatar
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    The way P0128 works, is that if the vehicle doesn't reach operating temperature within a certain time, the car assumes something is wrong. The engine is designed for the thermostat to fail open, for safety/longetivity. It then cuts your AC, coolant temp display on the dash, and also in my case sent the car into some weird mode that ran awful. Pulled timing, sluggish, etc... Also the car would turn the cooling fans on 100%, which keep temps on my car at 155-160*.

    When you disable P0128by setting the drop-down to 3-no error reported, it ignores the coolant temp logic. You don't lose AC, coolant temp display, and your fans work normally. I've been running a disabled P0128 for two years now with no issues.
    2008 Pontiac G5 2.2L (main oil seal became a crunchy Autumn leaf, RIP)
    2016 Fiesta 1.0L Ecoboost - Project "not-so-detestable"

  3. #3
    Yea pretty weird I know v8 guys do it just wasn't sure how it would work on hhr. So I wouldnt get the --- on digital display and engine n fans will work normal? Sounds good

    Thanks for confirmation
    Last edited by prostreet1967; 07-26-2015 at 08:35 PM.

  4. #4
    little problem, after setting p0128 to no error reported i let car run while working on door handle. after few minutes the abs and stabilitrack lights came on. turned car off and then it wouldnt restart. after charging battery for a while i started engine and checked charging system to find alternator is not putting out.
    could this be due to the p0128 or just a coincidence?

  5. #5
    Advanced Tuner CatnipG5Bandit's Avatar
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    Probably coincidence. My stock tune disabled the alternator for a few seconds after startup anyway. So no comment there. I'd assume something got touched, unplugged, or a fuse blown when working on the door handle.
    2008 Pontiac G5 2.2L (main oil seal became a crunchy Autumn leaf, RIP)
    2016 Fiesta 1.0L Ecoboost - Project "not-so-detestable"

  6. #6
    Need to find diagram. I did pull thermostat so prior to starting a filled n bleed cooling system and power washed engine. Never had issue before fuses ok n wiring ok at alternator

  7. #7
    Advanced Tuner Road's Avatar
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    Here you go good luck
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