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Thread: engine heater sets "engine hot" MIL ?

  1. #1
    Advanced Tuner
    Join Date
    Apr 2007
    Graz, Austria / Europe

    engine heater sets "engine hot" MIL ?

    weird issue somehow. Customer had a Webasto engine/interior pre-heater installed which has absolutely no connection to PCM and runs on gasoline.

    when engine is cold, he remotely starts heater to have it warm and comfy when he drives off, all OK at first, about 5 minutes later display shows "engine overtemp", MIL comes off and it is hard to start thereafter and coolant temp gauge is forced to 0. He needs to pull PCM fuse to get rid of it. If he does the same when engine is hot not problems at all.

    Spoke to a GM Tech today and he said he has seen that a few times on 2008 and up Silverados. Apparently, there is a engine off timer and first time when ignition comes on PCM (or BCM?) compares IAT with coolant sensors and compares it to a temperature table. If mismatch like coolant preheated to 50'S and IAT sees 10's, it "thinks" coolant temp sensor os failed and switches MIL on. BS or fact?

    it sort of spoils the idea of having a pre-heater......

    what are trucks doing who have the block pre-heater option? are the running a different OS? Anything I can do with HPTuners, GM is at a mess here at the moment due to the bankrupcy thing, means zero support in Europe

    anbody have a solution for that as it is winter and chilly.........

  2. #2
    Please email your file to support and I'll take a look at it next week
    I count sheep in hex...

  3. #3
    Tuner in Training
    Join Date
    Jun 2007
    bringing this thread from the dead....
    gm;s new block heater cord activates at around -18C or something.
    if you don't plug it in, this 09 denali 6.2 starts fine. plug in heater overnight and in -35deg temps, it starts rough and idles bad and dies.
    after a rough restart, idle smoothes and is okay im told. sometimes the engine overtemp and cel come on.
    does anyone know the intake temp tables vs coolant temp that I could alter to make this problem go away?
    I also have this issue once a year on my blower car. (2010 Camaro) overtemp warning on start due to 2 tempo sensors not reading within 9 degrees of each other.
    I cant seem to locate a relevant table on 2.24.

  4. #4
    Tuner in Training
    Join Date
    Sep 2015
    anyone, similar issues here on a 2010 5.3 with e38