98 Peterbilt cruise not working

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by drewfarmsllc, Aug 12, 2022.

  1. drewfarmsllc

    drewfarmsllc Bobtail Member

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    Oct 18, 2008
    South Carolina
    0
    I have a 98 379 with 12.7 Detroit and the cruise quit about 6 weeks ago. Jake's work fine. High idle works and can adjust rpm up and down with switch. I have a laptop and used jpro to check it. All the switches are working according to laptop. On off,resume and set, clutch and brake all are showing that it's working properly. Any ideas?
     
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  3. Goodysnap

    Goodysnap Road Train Member

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    Jul 12, 2017
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    Are you showing road speed in the ECM? Sometimes there’s 2 output speed sensors, one for the Speedo and one for the ECM.
     
  4. drewfarmsllc

    drewfarmsllc Bobtail Member

    46
    13
    Oct 18, 2008
    South Carolina
    0
    I replaced both sensors but that doesn't mean anything. How do I check that ?
     
    Rideandrepair Thanks this.
  5. Goodysnap

    Goodysnap Road Train Member

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    Jul 12, 2017
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    If the speed does not register you will need to check the wiring from the ECM to the sensor. Sometimes it’s just easier on an older chassis to just run a new twisted pair from the sensor to the ECM.
     
    Rideandrepair and spsauerland Thank this.
  6. Rideandrepair

    Rideandrepair Road Train Member

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    Aug 8, 2015
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    When I had that exact problem, it was the top speed sensor. Not the one on the bottom. Never knew about the second one, till I happened to notice it one day. Must have ran 2 yrs. that way. Thought I’d mention it, in case you’re wondering which one controls the cruise.
     
    Bean Jr. Thanks this.
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