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Thread: Fan On/Off Logic (GM Computer)

  1. #1
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    Fan On/Off Logic (GM Computer)

    I've read all of the posts dating back to 2006 about this topic but I STILL can not seem to get my fans to turn on and off properly (well.....on works....but not off). Attached should be an image of my settings in the editor. Hopefully someone has had this same issue. Again, the fans turn on as expected, but once they come on and the temperature drops below my set point, the logic never triggers the fan to off. I have monitored the values in the scanner and I can see that "fan1" comes ON but once the temp drops back below my transition temps, it still doesn't transition to off. I have put a volt meter on the fan output and it reads 12 volts. If I pull the fuse to the fan (in my fuse block), the fan goes off. Put it back in, fan comes on (once up to temp). And even when the temp drops below, pulling the fuse and re-inserting it, fan still stays on. So the computer is clearly still commanding it on. Turn of power to the computer and restart the vehicle, the bit is now "off" in the scanner and the fan is off. So.....any help anyone can give would be MUCH appreciated. Because I feel like I have tried everything and read all that I can.

    BTW: I've just started tuning work...so that is why I am new to this forum. But I am LOVING the flexibility it gives me when it comes to control of my newly boosted 2.2L ecotec motor. This work is in a 2008 GM computer that was in a Chevy Cobalt (should have mentioned that before). i've put this motor in an extreme rock crawler that I have recently finished building.
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    Last edited by four_by_nut; 01-02-2020 at 09:37 AM.

  2. #2
    Senior Tuner cobaltssoverbooster's Avatar
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    this may sound dumb but verify with the scanner that the ac system is not triggered and the ac system pressure is reading a low pressure value. if the system jumps to the ac fan tables it will be harder to control.

    the lowest cell for % vs etc needs to be 0 so it will command on off state and allow the relay to unlock.
    for the fan off at key, go to the ignition off column and select fan % = 0 and set fan hi to 100%.
    this will run the fan at 100% until the ecu shots down. if bellow the enable hi ect value then it will command 0% and unlatch the relay.
    ignition off - run-time max in stock 08 2.4 ecu is 780 seconds. that's like 13 minutes of after run allowable. if you want to test the shutdown option then set it to 30 or 60 seconds so your not standing there for ever waiting for the timeout override to end.
    run-time zone sets the ignition off run-time allowed for each zone. ect zone sets the ect shut off override temperature. so if in zone 2 i can run for 780 seconds, the ect zone is 221*F which if i fall bellow that before 780 seconds goes by, then it should shut down based on a coolant override.

    if your fan is not pwm compatible then you need to change the pwm requests to reflect that by saying 0 or 100 (99.99 or whatever the highest pwm value the software will accept).

    i dont think i have an exact solution but hopefully it offers insight to the operation and can help you adjust the system.
    rdrfabrication@gmail.com
    2016 GMC 3500 Denali Diesel
    2000 Ford Mustang - Top Sportsman

    Ecotec help can be found here:
    LNF-http://www.hptuners.com/forum/showth...357-LNF-Guides
    LSJ-http://www.hptuners.com/forum/showth...965-LSJ-Guides

  3. #3
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    Thanks cobaltssoverbooster for that response. Maybe I wasn't clear....I'm not having a problem when I turn the vehicle/rig off. I'm not having a problem getting them to come on when I want. I can't seem to get it to turn off once the ECT drops below my set value of 20%. I don't think the AC settings are interfering because it does come on when I want it to as the ECT climbs. But it won't go back off once the fans are on and the ECT drops below that 20% value.

    I'll double check my AC stuff tomorrow just to make sure that's not interferring.

    Any thoughts why the computer isn't commanding the fan off once the ECT drops back below my 20% setting?

  4. #4
    Senior Tuner cobaltssoverbooster's Avatar
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    set the 192 cell to 0. if the temp commands 0 there then it should shut down and bypass the pwm transition table.
    Last edited by cobaltssoverbooster; 01-13-2020 at 12:43 AM.
    rdrfabrication@gmail.com
    2016 GMC 3500 Denali Diesel
    2000 Ford Mustang - Top Sportsman

    Ecotec help can be found here:
    LNF-http://www.hptuners.com/forum/showth...357-LNF-Guides
    LSJ-http://www.hptuners.com/forum/showth...965-LSJ-Guides

  5. #5
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    Changed that value to 0 in the table and it still won't turn off once it comes on even when the desired goes below 20%. In fact it is sitting at 0% and the fan is still commanded on by the computer (verified with the scanner PID). I'm at a loss....

  6. #6
    Senior Tuner cobaltssoverbooster's Avatar
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    have you tried changing the fan 1 0 cell to 1? im wondering if 0 and 1 are fan selections. it sounds dumb but when logic isnt working time to try unusual changes.
    rdrfabrication@gmail.com
    2016 GMC 3500 Denali Diesel
    2000 Ford Mustang - Top Sportsman

    Ecotec help can be found here:
    LNF-http://www.hptuners.com/forum/showth...357-LNF-Guides
    LSJ-http://www.hptuners.com/forum/showth...965-LSJ-Guides