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Cadillac STS-V Series Forum Discussion, Engine hot ac off in Cadillac V-Series Forums; Time to ditch that mechanic....
  1. #16
    carter's_sts is offline Cadillac Owners Connoisseur
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    Time to ditch that mechanic.

  2. #17
    PGA2B's Avatar
    PGA2B is offline Cadillac Owners Connoisseur
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    Re: Engine hot ac off

    Robert- For future reference, you can do that for free at a local parts store.

  3. #18
    Robert Kimball is offline Cadillac Owners Member
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    What do I need to buy at the parts store?

  4. #19
    carter's_sts is offline Cadillac Owners Connoisseur
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    He's saying that auto parts stores can read and clear codes for you.

    You could also get your own scan tool if you want. I think mine was around $40.

  5. #20
    Cadillac Cust Svc's Avatar
    Cadillac Cust Svc is offline Cadillac Customer Service
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    Re: Engine hot ac off

    Quote Originally Posted by Robert Kimball View Post
    I had the same problem. New V owner. Took it to my mechanic and he said just needed a reboot of the computer....$ 100 later. It went away for 5 days and them same error popped up. Read the posts in this forum and disconnected the battery posts as suggested and all is going good....... So far. My mechanic charged me $100 to reset the computer?????
    Hello Robert,

    Welcome to Cadillac Owners! We are happy to have you part of the community. I hope you are enjoying your V ownership so far. I am sorry you experienced an issue with your engine temperature gauge. I am glad the issue seems to be resolved for you currently. If additional concerns or questions arise, please contact us via private message so we can assist. Gregory and I monitor the Cadillac forums and are here to help.

    Sincerely,

    Laura M.
    Cadillac Customer Care

  6. #21
    LEGACY_GN is offline Cadillac Owners Fanatic
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    Re: Engine hot ac off

    Please don't waste your money on a thermostat. This is a known common issue with our cars. I have a bluetooth obd scan tool in my car just for resetting that code on the fly with my android phone without unhooking the battery. My friend replaced both temp sensors in his V and it still happens to him. Just accept it and move on. The thermostat is fine. The other known issue but not quite as common is the shift to park glitch, but I'll save that for another time. Someone really needs to make this a sticky at the top of this forum to let everyone know.

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    http://www.ebay.com/itm/v1-5-Super-M...-/400553914660

  7. #22
    rbzstsv is offline Cadillac Owners Fanatic
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    Quote Originally Posted by LEGACY_GN View Post
    Please don't waste your money on a thermostat. This is a known common issue with our cars. I have a bluetooth obd scan tool in my car just for resetting that code on the fly with my android phone without unhooking the battery. My friend replaced both temp sensors in his V and it still happens to him. Just accept it and move on. The thermostat is fine. The other known issue but not quite as common is the shift to park glitch, but I'll save that for another time. Someone really needs to make this a sticky at the top of this forum to let everyone know.

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    http://www.ebay.com/itm/v1-5-Super-M...-/400553914660
    Wrong. Replace your tstat. Common issue most of us have had.
    mjs182004 likes this.

  8. #23
    LEGACY_GN is offline Cadillac Owners Fanatic
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    Re: Engine hot ac off

    Well, you can buy a thermostat, spend and hour replacing it or hundreds paying someone to replace it, or simply unhook and rehook your battery. One of them will fix it, just have to decide on which one you want to try first.

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    Quote Originally Posted by iLuvEasy View Post
    Thanks I disconnected the battery and it reset it self but I'm still take it to get looked at or a pressure check done on the radiator
    I guess it wasn't the thermostat, imagine that.....

  9. #24
    CMNTMXR57 is offline Cadillac Owners Enthusiast
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    Re: Engine hot ac off

    Clearing the code isn't FIXING the problem though. And in some places, like here in the Chicago area, where cars get emissions tested, one of their parameters is "Mileage since last DTC cleared" (this is also maintained in the history section of the Diagnostic Trouble Codes section that is viewable on a Tech2 or any other similar professional level scan tool). Which means if you're resetting it frequently and not fixing the initial problem, it will flag if their mileage criteria isn't met and you will fail the test, which also here, until you pass, will keep you from re-registering your plates. Wussyconsin ties registration to the emissions test too, albeit the last time I tested a car up there, they did not factor in "mileage since last DTC cleared" as a parameter. The problem is with the T-stat as all of us have experienced and requires replacement. Plain and simple.

    Resetting the PCM by unhooking the battery is also doing more than just clearing codes and turning off the MIL. It is basically puts the PCM into idle re-learn mode. It's kinda like rebooting your PC at home after it's been running for the last month. It clears all the cobwebs out and blows away the bad learned habits, which includes clearing current DTC's (However it does put them into a history file...). This gives you the opportunity to retrain it the way YOU like it. There is actually a whole GM OBDII idle re-learn driving cycle to get the most out of the re-learn. HOWEVER, to the extent that a fault is there as would be the case with a faulty t-stat, the code will regenerate once either a failure actually occurs or the I/M system runs a readiness check. At which point, you're right back to square one.

  10. #25
    Guy.Seminerio is offline Cadillac Owners Connoisseur
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    Re: Engine hot ac off

    And how long does this readiness check take to happen. I got the message on the 15th of July, did the battery thing and 3 months and a few thousand miles later (daily driver) it hasn't come back.

  11. #26
    CMNTMXR57 is offline Cadillac Owners Enthusiast
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    Re: Engine hot ac off

    A few thousand is more than sufficient. I think it's usually like a couple hundred miles. They (speaking for Illinois EPA here), want to make sure that you didn't just clear it while sitting in line to be tested.

    The I/M system (referred to as "Readiness Monitors"), will run tests on supported parameters at random. UNLESS it runs a test (lets use a catalyst test as an example), that fails and generates P0420, it will then continue to run that test each ignition cycle until it runs and passes. It will then clear the DTC and turn off the MIL. If it runs and passes, remaining clear for a pre-determined number of subsequent tests (usually 3 - 7 successful, consecutive operating cycles), after, it will clear the current DTC cache, and put it into a history cache and that takes 40 or more sucessful, consecutive operting cycles before being completely purged.

    With a Tech2 (or other suitable tool), you can actually trigger the test manually if you're troubleshooting it. But otherwise, it's completely random and at the PCM's will.

  12. #27
    PGA2B's Avatar
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    Re: Engine hot ac off

    Quote Originally Posted by CMNTMXR57 View Post
    Clearing the code isn't FIXING the problem though. And in some places, like here in the Chicago area, where cars get emissions tested, one of their parameters is "Mileage since last DTC cleared" (this is also maintained in the history section of the Diagnostic Trouble Codes section that is viewable on a Tech2 or any other similar professional level scan tool). Which means if you're resetting it frequently and not fixing the initial problem, it will flag if their mileage criteria isn't met and you will fail the test, which also here, until you pass, will keep you from re-registering your plates. Wussyconsin ties registration to the emissions test too, albeit the last time I tested a car up there, they did not factor in "mileage since last DTC cleared" as a parameter. The problem is with the T-stat as all of us have experienced and requires replacement. Plain and simple.

    Resetting the PCM by unhooking the battery is also doing more than just clearing codes and turning off the MIL. It is basically puts the PCM into idle re-learn mode. It's kinda like rebooting your PC at home after it's been running for the last month. It clears all the cobwebs out and blows away the bad learned habits, which includes clearing current DTC's (However it does put them into a history file...). This gives you the opportunity to retrain it the way YOU like it. There is actually a whole GM OBDII idle re-learn driving cycle to get the most out of the re-learn. HOWEVER, to the extent that a fault is there as would be the case with a faulty t-stat, the code will regenerate once either a failure actually occurs or the I/M system runs a readiness check. At which point, you're right back to square one.
    Well stated!

    I got the issue, replaced the T-Stat and have not gotten the code since and its been a couple of years ago now.

  13. #28
    Guy.Seminerio is offline Cadillac Owners Connoisseur
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    Re: Engine hot ac off

    Not sure how the failed tstat triggers the code but could it possibly incorrectly read the tstat as malfunctioning, therefore throwing the code when in reality there's nothing wrong? Or maybe there is a slight fault in the tstat for a split second that causes the car to throw the code which stays on even though the tstat only malfunctioned for a second?

  14. #29
    carter's_sts is offline Cadillac Owners Connoisseur
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    The code gets set when the engine doesn't heat up to a certain temperature in a certain amount of time. So a T-stat that opens too soon will cause it.

    It's a stupid check they have in place. And it says the engine is hot, which it isn't and disables the temp gauge.

  15. #30
    CMNTMXR57 is offline Cadillac Owners Enthusiast
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    Re: Engine hot ac off

    When you first start your vehicle, it is running in what is called "open loop" operation. What that means is, it reverts to base programming in the PCM to let the cold engine run. In order to do so, it ignores readings from some of the battery of sensors the vehicle has. HO2S's (Heated Oxygen Sensors), ECT (Engine Coolant Temp), and potentially many others. It can vary from vehicle platform to vehicle platform. When running in open loop operation, it is typically running richer than normal. This results in excess fuel consumption and of course, dirtier emissions. Think of it as a modern day equivalent of running a carbed car with it's choke on and a heat riser off the exhaust manifold into the air cleaner assembly.

    So as the vehicle warms up, it reaches a certain threshold and flips into it's proper "closed loop" operation. It will then be utilizing all the sensors, and once in use, they properly meter A/F and ignition tables for optimum fuel efficiency and emissions compliance. In this case, if the ECT can't reach optimum regulating temps due to a stuck t-stat within a certain pre-dertmined time frame, then you risk not getting into "closed loop" operation.

    In particular, P0128's purpose is that it monitors the performance of the thermostat, by using the ECT sensor to determine if the engine coolant will increase at the correct rate, and also meet the calibrated target temperatures under various operating conditions.

    The ECM uses the start-up ECT and the start-up intake air temperature (IAT) to begin the diagnostic calculation. The air flow into the engine is accumulated, and vehicle speed, distance, and engine run time are also factored in to determine if the ECT does increase normally and reach the calibrated target temperatures.


    On another note, in regards to the I/M system, ours doesn't support any ECT test, so no worries on any readiness montior activity. It is purely a regular fault diagnostic that when triggered will cause you to fail any emissions test. I had mine hooked up to the T2 today and figured I'd check my I/M system status. You can see, at least for 2006, we only have 4 monitors. Those being Catalyst, EVAP system, O2 sensors, and the O2 sensor heater circuit.

    Guy.Seminerio likes this.

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