Engine Hot - AC Off and P0128; Thermostat Replacement
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  • 5 Post By Guy.Seminerio
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Cadillac STS-V Series Forum Discussion, Engine Hot - AC Off and P0128; Thermostat Replacement in Cadillac V-Series Forums; I know most of us know how to do this but I decided to take a couple of pictures while ...
  1. #1
    Guy.Seminerio is offline Cadillac Owners Connoisseur
    Automobile(s): 2009 STS-V; 1979 Coupe Deville
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    Engine Hot - AC Off and P0128; Thermostat Replacement

    I know most of us know how to do this but I decided to take a couple of pictures while I was replacing the thermostat so I could post them for anyone who needs it in the future.

    To start off, If you get the "engine hot - AC off" message, most likely, the problem is your thermostat. This also applies to a check engine light with the code P0128. Tim did a write up on why this problem occurs here http://www.cadillacforums.com/forums...explained.html. It is a common problem on the car.

    If the message pops up, your AC will obviously cut off so this will cause an uncomfortable situation, especially if you have friends or family in the car with you. So pull over somewhere, turn the car off, disconnect the battery cables, touch them together for a few seconds and reconnect them. The issue should go away. It may go away for a few minutes, a few weeks, or a few months but at least you and your passengers will have air conditioning. I managed to get about 6 months out of it. Either way, the battery disconnect should be a temporary fix and in the meantime you should go ahead and get the new thermostat on order. Also, in my experience, with the "engine hot a/c off" code, I could go some time after a battery disconnect without any issues, whereas with the engine light AND the P0128, as soon as the battery is reconnected and the car is started up, the symptoms return. You can get the "engine hot ac off" message without the CEL, but if you have the CEL with P0128, you will always have the "engine hot ac off" message with it. Just my experience.

    I ordered from Chris at Rippy Cadillac as I do all my parts.

    Thermostat part number is 12601556, list price $23.24, Chris' price $14.51.
    Gasket part number is 12590871, list $8.57, forum discount is $5.35.

    After tax and shipping I paid $28.26.

    I've read that people re-use the old gasket, but I went ahead and changed it out.

    Make sure you haven't driven the car for hours before you do this job. Let it sit overnight and do it in the morning so you don't make so much of a mess with the coolant, or burn yourself with it.

    --------------------------------------

    Under the hood, remove the black plastic sight shields. You'll see something like this:



    The blue circle is where the thermostat is housed.

    The red arrow shows that I removed the part of the intake between the MAF/air filter and the Y portion (yellow circle.)

    I have the Y portion of the intake circled to note that if this is removed, you will have a much easier time squeezing your hands in there and working. I didn't do this. It was very tight down there. You'll end up moving some hoses around to help you maneuver down there a little better. I have my engine appearance cover on because the car is for sale.

    Here's a close-up:



    there are 2 10mm bolts to be removed (blue arrows) (one of them is not in view here) and a socket wrench might not be the best solution with the tight quarters. You might find a regular wrench to be better.

    There are 2 clamps to be removed (red arrows) (I used large adjustable pliers.) I actually didn't remove the smaller of the two hoses because I had issues doing so, but things would probably have been easier if I did. Understand that when you remove these hoses, coolant will spill onto the aero shields on the bottom of the car and collect in a puddle down there unless you remove them before you begin. Can you guess whether I thought of that beforehand? SO have some 50/50 dexcool handy to top off when you're all done.



    Red arrow: You see I found a convenient place to rest the big hose so I didn't loose too much coolant.
    Blue arrow: You see I didn't remove the small hose.
    Yellow arrow: Old thermostat.
    Green arrow: Old gasket (black rubber piece)



    Red arrow is the new tstat and the new gasket

    Blue arrow is the old gasket still in the now empty housing.

    I used needle nosed pliers to remove the old gasket. It didn't seem possible to get the new thermostat into the old gasket unless you removed it first. So since I had to remove it anyway, I said screw it and used the new gasket. You have to use a gasket sealer. I used the sealer in the little cutout of the gasket where the thermostat sits, and in the housing where the gasket sits. I followed the instructions on the bottle of the sealer which called for pressing it into place and letting it sit for a few hours before handling it.



    New tstat and gasket sitting in the housing. I hadn't put the sealant in yet. I placed it in and took a photo. Then I removed it and put in the sealant, let it sit for a few hours, then put the housing with thermostat back in, put the 10mm bolts back in, reconnected the big hose, disconnected battery cables, touched them together and reconnected them to reset the CEL, and fired the car up. Problem solved. By the way, I didn't have to top off coolant. Although I thought I lost a lot, the coolant level in the reservoir was still slightly above the normal cold level. For the next couple of days, I checked the coolant level in the mornings and I was good to go.

    After disconnecting the battery, you'll lose a couple of settings. The automatic window up/down needs to be reset. Open your window by pressing the switch in the FULL down position and HOLD the button in that full down (2nd click) position the entire time the window is opening. When the window fully opens, continue to HOLD the button in that full down position for another 2-3 seconds. Then immediately pull the switch in the full up position (2nd click) and HOLD it there until the window is fully closed. Repeat this on all windows. If the feature is not restored in one of the windows, do the procedure again in that window alone.

    If you have a 2009, the HUD exceed speed limit alert will default into the OFF position after a battery reset. You'll have to turn that back on.

    Also, if you're as entertained by a british guy giving you nav directions as I am, you'll realize that after a reset, the nav defaults to the U.S. female setting after the battery reset.

    A lot of experience on here so I'd love to see others chime in with their pointers, especially those who went with the gasket re-use route.

    Other than that, this was something I was hoping to find before I did this job and it wasn't available so hopefully this will come in handy for someone else in the future.

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  3. #2
    Berger 93 is offline Cadillac Owners Fanatic
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    Re: Engine Hot - AC Off and P0128; Thermostat Replacement

    Great write up . . too bad too many dealers are too ignorant to understand this simple fix.

  4. #3
    Guy.Seminerio is offline Cadillac Owners Connoisseur
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    Re: Engine Hot - AC Off and P0128; Thermostat Replacement

    Thanks. Yeah my understanding is they don't assume thermostat and will try a laundry list of other things to solve it.

  5. #4
    Ludacrisvp's Avatar
    Ludacrisvp is offline Cadillac Owners Connoisseur
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    Re: Engine Hot - AC Off and P0128; Thermostat Replacement

    ^^ so they can make more money.
    Its a complex car so it can't be the simple fix ... ever.
    Guy.Seminerio likes this.

  6. #5
    Jailtime is offline Cadillac Owners Fanatic
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    Re: Engine Hot - AC Off and P0128; Thermostat Replacement

    Nice how-to.

    I didn't have to remove any hoses from the housing when I did mine, but I pulled the Y part of the intake. Lots more room that way.

  7. #6
    Guy.Seminerio is offline Cadillac Owners Connoisseur
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    Re: Engine Hot - AC Off and P0128; Thermostat Replacement

    Thanks.

    And yeah if I have to do it again, the y part is coming out.

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