Auto fan randomly working in 379 with Detroit 60

Discussion in 'Peterbilt Forum' started by simonsocm, May 18, 2021.

  1. Don379

    Don379 Medium Load Member

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    Is your a/c on? If sitting idle, the fan will come on to cool the a/c condenser about every 30. -60 seconds. If so, that tells me everything is good with your solenoid. I would be looking at your coolant temp sensor as being the problem if it’s not cooling the radiator when needed
     
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  3. simonsocm

    simonsocm Light Load Member

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    Yup, AC was on. I will talk to a detroit dealer and see if there's maybe a coolant switch for the fan or if maybe the gauge reads off a different sensor. If the gauge reads off a different sensor like Lester was saying then yeah the engine temp sensor is borked then for sure.
     
  4. simonsocm

    simonsocm Light Load Member

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    Well I replaced the radiator and the coolant temp sensor for the ecm. Still not turning on when it should. When I get home next week I'm going to check the wiring to the coolant temp sensor from the ecm.
     
  5. Don379

    Don379 Medium Load Member

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    should be throwing code if there is no signal to the sensor. Did you check for codes with cruise control switch
     
  6. simonsocm

    simonsocm Light Load Member

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    Nope, no code for coolant temp sensor. I'd assume it would've said something along the lines of voltage high if the resistance was super high. I'm still going to check the wiring when I get home next though. Only code I had was for a high voltage for coolant level sender that I just temporarily fixed with a butt connector and lots of electrical tape for stability and sealing.

    Not a thing for the coolant temp sensor.
     
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  7. simonsocm

    simonsocm Light Load Member

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    I had a thought on this. Could something like an intermittent bad ground for the sensors cause something similar to this? Or would that throw codes?

    Also where would the instrument panel ground be located? Maybe it truly is the coolant temp gauge and coolant warning switch has an intermittent dirty ground.
     
  8. Don379

    Don379 Medium Load Member

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    All those sensors go to ecm. IF bad ground and sensor wasnt working, you would throw a code. All you have to do to check and see if this is accurate is next time you have truck running, unplug the sensor and see if check engine light comes on. It should. Why do you want to check grounds to instrument panel? Everything works on instrument panel correct? I think what you need is for a diesel shop to plug into ecm with laptop. This would tell you immediately where the fault is if any at all. If funds allow, you should buy the communicator and software for your laptop.
     
  9. simonsocm

    simonsocm Light Load Member

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    I've had a shop check the radiator fan function and they said it came on at the correct temp but my gauge is 15 degrees off. Thing is my coolant temp warning switch also comes on when the gauge shows 215... Most of the time. So fan comes on around 219 on the gauge, but shows 204 in ecm, coolant warning temp comes on at 215-220 on the gauge.

    All the other gauges seem to work as intended still.
     
  10. Don379

    Don379 Medium Load Member

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    with the computer hooked up, you can see in detail the functions what the computer in your truck sees.
     
  11. simonsocm

    simonsocm Light Load Member

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    Been awhile, did some poking around this weekend. Fixed an ecm power issue and cleaned the ecm connections with electrical contact cleaner. I also checked ohms from the ecm to the coolant sensor and got 0 ohms. Same with the ecm grounds.

    I think I'm gonna check if the sensor is actually getting 5v or not. If its getting 5v then I'm gonna assume the ecm is going bad. If its not getting 5v then I'm guessing maybe a bad spot in the harness?
     
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