1999 Freightliner Classic DDEC 4

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Smellfunny, Feb 21, 2024.

  1. Smellfunny

    Smellfunny Road Train Member

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    Having issue with coolant temperature gauge in dash and fan control not seeing correct coolant temperature. ECM shows proper reading but the dash gauge is jumping and engine fan coming on. I am thinking there may be a wiring issue from ECM to cab but not sure which wire that could be. Or if it may even be the EDM in the dash.
     
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  3. Big Road Skateboard

    Big Road Skateboard Road Train Member

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    Unplug your fan solenoid and see if your gauge settles to normal.
     
  4. wtwfarms2018

    wtwfarms2018 Bobtail Member

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    I thought engine fan on those were controlled by the ecm.
     
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  5. Smellfunny

    Smellfunny Road Train Member

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    If that makes the gauge work would it be the solenoid?
     
  6. Rideandrepair

    Rideandrepair Road Train Member

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    Don’t know about your gauge. I do know for sure there was a bulletin on the fan. I did the upgrade on my 99. It involves a wire splice into the harness near the solenoid. Easy fix. Did it in parking lot at Youngstown Freightliner. Had the problem for years before I heard about the bulletin. Fan would come on for no reason. Wintertime, stopping to pay a toll for example. No one else seemed to know anything. Finally Youngstown came through with an actual upgrade kit. They even loaned me a fancy crimp tool. I mentioned it to them a few years back. No one knew anything. Lol. My 2000 has a pdmi box in the fuse panel that controls the fan, and a few other things. Eliminating a few sensors. Memories a bit rough. See if you have a pdmi box. If not, maybe you need the upgrade kit if it can be found.
     
  7. Big Road Skateboard

    Big Road Skateboard Road Train Member

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    Yes.



    They are, but that signal goes through the Coolant Level Sensor Module on the Freightliners, which interfaces with several other outputs
     
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  8. jamespmack

    jamespmack Road Train Member

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    Most, Not all had mechanical Gauge from factory.
     
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  9. Smellfunny

    Smellfunny Road Train Member

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    Unhooking the fan solenoid made no change. He said it does not mess up as much once the engine is hotter. But when cold the gauge is wonky and the fan kicks on and off.
     
  10. jamespmack

    jamespmack Road Train Member

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    Sticking thermostats will cause mechanical gauge to be in accurate/or all over the place. Possibly causing a ecm coolant temp sensor to see a overheat situation and cycle the fan.

    Or you have a head gasket/liner issue about to show its face.
     
  11. Big Road Skateboard

    Big Road Skateboard Road Train Member

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    See if it's a mechanical gauge, possibly fan control too, but shouldn't be on that engine.

    A pic of the right rear of the head, just below the valve cover, and a pic of the thermostat housing would verify
     
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