cruise not working

Discussion in 'Trucks [ Eighteen Wheelers ]' started by gunner76, Nov 19, 2014.

  1. gunner76

    gunner76 Medium Load Member

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    We have a '99 FL112 Freightliner and the cruise has stopped working, this also means that we lost the ability to bump up the idle. Trying to figure out what the problem is and here is what I've found so far.

    This truck is set up so when the cruise switch is in the "on" position the jakes will only turn on when the brake pedal is pushed, when the cruise switch is off the jakes will engage when you let off the throttle. Right now when the jakes are on standby they will turn on when you let off the throttle no matter the position of the cruise switch. Also when the cruise switch is off you can hold the set/resume switch to run a diagnostic scan for any stored codes.


    I thought it might be the cruise on/off switch so I replaced it and there was no change. Next I replaced the stop light pressure switch that is mounted on one of the airvalves on the firewall and that made no difference. I don't think it is the set/resume switch since I can activate the code scan feature using it and I don't believe it is the switch down by the clutch pedal because if that was bad the jakes shouldn't turn on either.

    Anybody have any ideas on what it could be?
     
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  3. Alaska76

    Alaska76 Road Train Member

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    Do the brake lights work? Many cruise systems rely on an operational brake light circuit, as that is one way to cancel the cruise control.
     
  4. gunner76

    gunner76 Medium Load Member

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    brake lights work. I'll probably just have to take it somewhere and have a professional look at it, although it'll be at least a week before we can spare the truck.
     
  5. JohnP3

    JohnP3 Road Train Member

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    One thing you could test is the speed sensor on the back of the transmission, if you have a Ohm meter, test both coils one should be around 900 and the other between 1100 and 1400, if you do not have a meter swap the leads, and inspect the wires. You may need to have it put on a computer to find the problem, testing each switch, diagnostics by the ripping and tearing method very rarely works, and is expensive. The 900 Ohm coil lead should go to the computer.
    You want to tell us what engine you have!
     
  6. GrapeApe

    GrapeApe Road Train Member

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    For high idle, the speed sensor should not be an issue because the truck should not be moving. The VSS is big a factor for the cruise control to work properly, but the high idle usually works when the VSS fails.

    I'm assuming that it's a Cat if you pulled flash codes from the cruise switches? If so, then the set/resume switch is working. To test the on/off switch, turn it on and try to pull codes again. If you can, the ECM is not seeing the on/off switch. It will only pull flash codes with the switch off, so if it wont pull them with the switch on, those 2 switches and wiring are OK. If it pulls code with the switch on, diagnose the problem in the on/off switch circuit.

    You have a parking brake switch and clutch switch circuits to check as well.
     
  7. Trckdrvr

    Trckdrvr Heavy Load Member

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  8. gunner76

    gunner76 Medium Load Member

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    GrapeApe is correct, it's a C12. The on/off switch for the cruise is also working fine because I can't run the code scanner with the switch in the on position.

    By clutch switch do you mean the spring loaded one that the pedal pushes against? I figured that if that switch was stuck in a position that wouldn't allow the cruise to work that the jakes also would be dead.
     
  9. sunsation288

    sunsation288 Light Load Member

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    Just a question , i try to figure what mean .... pull flash codes ?
    thanks in advance for taking time
     
  10. GrapeApe

    GrapeApe Road Train Member

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    With a Cat engine, you can use the cruise control switches to get engine diagnostic codes. With the cruise on/off switch "off", hold the set/resume switch either way for a few seconds and the check engine light will flash out 2 digit diagnostic codes. If there are no active codes, it will flash 5-5.

    Knowing that, if you can get flash codes it verifies that the set/resume switch is working correctly. You can verify that the on/off switch is working correctly if you can get flash codes with it off but not when it's on.
     
    sunsation288 Thanks this.
  11. postmandav

    postmandav Medium Load Member

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    We had a Volvo at a former company that had an issue with the cruise not working. I happened to be driving one day and accidentally pushed the clutch pedal up. All of ;a sudden the cruise started working. Maybe you have to much freeplay in your clutch pedal.
     
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