1997 pete 379 engine fan won’t cut in for engine temp

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Junk Yard Dogg, May 31, 2020.

  1. Junk Yard Dogg

    Junk Yard Dogg Bobtail Member

    10
    1
    Jun 21, 2013
    winnipeg manitoba canada
    0
    I have a 1998 pete 379 c12 (9ns).
    For the longest time my engine fan wouldn’t come on when my coolant temperature got high so I just used the manual dash switch. Never fixed this issue. Problem 1

    Problem 2 my engine fan now stays on constantly with engine fan dash switch off, my fan air solenoid is constantly getting power when key switched on.

    A wiring diagram would be great.
     
    Last edited: May 31, 2020
  2. Truckers Report Jobs

    Trucking Jobs in 30 seconds

    Every month 400 people find a job with the help of TruckersReport.

  3. A5¢

    A5¢ Medium Load Member

    344
    476
    Oct 30, 2017
    0
    the first three posts on the Mechanics page, has listings for Cat, Cummins and Detroit wiring diagrams. Check for it there. If it's not, ask pushbroom to kindly look it up.
     
    pushbroom and BoxCarKidd Thank this.
  4. RocketScott

    RocketScott Light Load Member

    231
    112
    Apr 10, 2013
    Tacoma, WA
    0
    Sounds like a bad sensor

    Weird that it would flip from being constantly open to constantly closed
     
  5. Junk Yard Dogg

    Junk Yard Dogg Bobtail Member

    10
    1
    Jun 21, 2013
    winnipeg manitoba canada
    0
    I think the 3406e 40 pin diagram is the same as c12, so I’m working off that to trace the system. I’ve changed the temp sensor and still had the same problem. I think the relay lost its ground, but I’m gonna start from the bottom up and hopefully report back with some findings.
     
  6. lester

    lester Heavy Load Member

    915
    2,309
    Jan 2, 2012
    NW, Iowa
    0
    Just FYI, I'm not sure about the c-12, but a C-15 doesn't kick fan on until 217 degrees
     
  7. pushbroom

    pushbroom Road Train Member

    1,531
    6,172
    Sep 1, 2012
    0
    Jump the a/c high pressure switch. Usually switch or the a/c circuit. If you can get it on a laptop it should tell you what is turning the fan on
     
    Goodysnap Thanks this.
  8. jcarter

    jcarter Bobtail Member

    5
    1
    Jan 21, 2018
    0
    Check the ac switch it can cause that
     
  9. Junk Yard Dogg

    Junk Yard Dogg Bobtail Member

    10
    1
    Jun 21, 2013
    winnipeg manitoba canada
    0
    So we finally found the cause of constant engine fan. Wire 226 out of the manual fan switch to the fan air solenoid had constant power When it shouldn’t have. There are 2 wires labeled 226 that come out of the manual switch one runs to the air solenoid and the other I’m guessing was a open jumper to nothing, but it looks like it somehow “plugged” into another open jumper with constant ignition power.
    Sounds weird but there has been no work done behind my dash before this problem started, and they were just barely making contact not like it had been physically put together.
     
    tommymonza Thanks this.
  • Truckers Report Jobs

    Trucking Jobs in 30 seconds

    Every month 400 people find a job with the help of TruckersReport.

  • Draft saved Draft deleted