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speedometer wont go over 40mph

Discussion in 'Ford Trucks' started by Scenic Lawnscape, Nov 2, 2009.

  1. Scenic Lawnscape

    Scenic Lawnscape Senior Member
    Messages: 481

    I have a 99 f-350 4x4 auto powerstroke

    My abs light was on and the speedo wasnt working till i hit over 40mph, well yesterday i was driving and it wont go over 40 mph.

    So I replaced the sensor in the Rear Diff, and now the speedo works fine untill I get to 40MPH and it wont go any higher.

    Any ideas?

    This is driving me crazy
     
  2. Bolt-1

    Bolt-1 Senior Member
    Messages: 103

    I wish i could help you with your dilema. It's always a PITA to have a vehicle prob. and the solution is out of reach. Unless it starts affecting performance, or ends up causing another issue. I don't see the problem. And look at it this way. If it only reads up to 40 mph. Think of the low mileage you'll have in a few years when you sell it.
     
  3. Scenic Lawnscape

    Scenic Lawnscape Senior Member
    Messages: 481

    the mileage is still working and working and so is the trip counter.
     
  4. Bolt-1

    Bolt-1 Senior Member
    Messages: 103

    Oh well, wishful thinking for you on my part
     
  5. Scenic Lawnscape

    Scenic Lawnscape Senior Member
    Messages: 481

    thanks anyways
     
  6. ProScape Canada

    ProScape Canada Junior Member
    Messages: 17

    there are two sensors on your truck. one's in the diff and the other is mounted on your frame. Ones low speed ones high speed and the one in your diff controls your truck shift points.
     
  7. albhb3

    albhb3 PlowSite Veteran
    Messages: 3,510

    but officer my truck said I was only going 40 hahaha
     
  8. Scenic Lawnscape

    Scenic Lawnscape Senior Member
    Messages: 481

    the one on the frame do you know what it is called
     
  9. Scenic Lawnscape

    Scenic Lawnscape Senior Member
    Messages: 481

    i found that there is a sensor on top of the trans but I cant seem to find a away to get it out
     
  10. smoore45

    smoore45 Senior Member
    Messages: 526

    So maybe they changed a few things from 99 to 03, but here is what I think is going on. If your ABS light came on when all of this started then it is a problem with the sensor in the diff. Now that you have replaced that sensor and you are still having problems, it could be the wiring going to the sensor. Did you check that the connector wasn't corroded or damaged? Maybe the seal is getting worn and letting water in it.

    The sensor on the transmission is your Output Shaft Speed (OSS) Sensor and is the one that controls your shift points(at least in my 03). Is your truck still shifting a driving okay? If yes, then I wouldn't touch the sensor on your Trans and try to see if you can find something with the wiring on the rear Diff sensor.

    Take this for what it is worth, I'm just going off of experience from my 03.
     
  11. RepoMan207

    RepoMan207 PlowSite Fanatic
    from Maine
    Messages: 5,033

    gee, Do Fords not have speed sensors on there hub assemblies?
     
  12. smoore45

    smoore45 Senior Member
    Messages: 526

    Thats a good point. They do in the front, but not in the rear(diff sensor only). If your 99 has 4-wheel ABS instead of just Rear ABS, then it could be one of your front wheel speed sensors(at the wheel end). In that case you may want to get a code checker from Autozone and see if you can figure out which one it is.