Jake Brake not working Cruise control working

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Tama Mai Hawaii Nei, Oct 1, 2020.

  1. Tama Mai Hawaii Nei

    Tama Mai Hawaii Nei Light Load Member

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    Sep 6, 2013
    Las Vegas, NV
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    I need some help. My Jake brake isn't working. I turn it on nothing not even a indicator light on dash comes on. Cruise works I can set it at idle and raise rpms.

    The engine is a c13 Lee15325 truck is a 386 Pete vin 750952

    I replaced the injector harness, put 6 new injectors in, and ran a overhead. The jakes didn't work prior to this but after completing the work jakes still don't work.

    We hook the computer up and no codes show.

    I thought it was the clutch switch but cruise control works. We even replaced the throttle sensor and wiring harness.

    Any ideas
     
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  3. stillwurkin

    stillwurkin Road Train Member

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    My engine brake will not come on if i am driving with my foot ( not cruise) if i have the cruise switch in the on position. I can put the engine brake switch on and there's nothing..switch the cruise switch off and engine brake starts. Then, if lets say i have the cruise set at 65mph and am gaining speed downhill. Speed has to get to 68mph or so, then engine brake starts. This is on a c-15.
     
  4. Goodysnap

    Goodysnap Road Train Member

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    Do you have power to the dash switch? There is no light on the dash. Does the light on the on/off switch come on? If the switches are used daily, they do not last forever and I replace quite a few.

    Next step is to connect CAT ET and check to make sure all the switches are responding correctly in the ECM.
     
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  5. Tama Mai Hawaii Nei

    Tama Mai Hawaii Nei Light Load Member

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    Las Vegas, NV
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    I get power to the dash switch. The CAT ET showing no faults. Originally it showed the number 1 injector had issues that lead to just replacing all the injectors then we noticed the wiring harness was screwed up.

    After we did all the work everything was fine no faults, looked to see if jake is on the brake peddle but it is set for the throttle.
     
  6. Tama Mai Hawaii Nei

    Tama Mai Hawaii Nei Light Load Member

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    Sep 6, 2013
    Las Vegas, NV
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    I never checked to shut the cruise off. I do know the cruise works though.
     
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  7. pushbroom

    pushbroom Road Train Member

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    CAT Et wont show any faults if the switch doesnt work.
    The switch input needs to be monitored in CAT ET
     
  8. stillwurkin

    stillwurkin Road Train Member

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    I had a mechanic that did a test drive for a different issue. He said your engine brake doesn't work. Same thing. I got in and it worked fine. Just have to have that cruise switch off.(thats when drivin Hope that solves your issue.
     
    Tama Mai Hawaii Nei Thanks this.
  9. AModelCat

    AModelCat Road Train Member

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    The jake can work just fine with the cruise on. Its a parameter that can be set.

    Like Pushbroom says, use ET to see if the ECM registers an input from the jake switch. It won't throw faults for a switch (and related wiring) issue since the ECM only recognizes voltage or no voltage.
     
  10. Tama Mai Hawaii Nei

    Tama Mai Hawaii Nei Light Load Member

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    Sep 6, 2013
    Las Vegas, NV
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    So an update used the ET program at Rush they said all parameters are where they're supposed to be. The jake is set to manual so should work on the peddle.

    I tried turning cruise off completely and still dont work. Im guessing its wiring issue.

    PSA: If you are running I15 between Vegas and Cali and you come up on me I apologize now in advance. I come down those grades in 8th gear and Cajon Pass in 7th. My jakes still not working and I don't want to smoke my breaks.
     
  11. north60

    north60 Bobtail Member

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    Jun 13, 2019
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