Thread: diagnosing speedometer not working

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  1. #1 diagnosing speedometer not working 
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    Also getting the "CAL" message on the overhead console and a CEL for lack of input from the speed sensor. Problem arose when I put my t-case back in a year ago after replacing the front half. I've tried rotating the speedo gear on the case with no change. Before I start tracing wires, I'm wondering if anyone knows exactly what triggers the CEL when it says lack of input from speed sensor. Can it tell through other methods that the vehicle is moving and it says hey wait a minute we're missing something, or could it just be a short in the wiring for the VSS somewhere? Previous to pulling the case, the speedo would take a few minutes before it would actually start working too, I'd have to drive half a mile or so before it would kick on. Makes me think I'm looking at a wiring issue, and I hate those.
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  2. #2 Re: diagnosing speedometer not working 
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    Hopefully something simple like your exhaust burned the wire going to the vss on the tail cone. Good luck


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  3. #3 Re: diagnosing speedometer not working 
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    I've given the wires a decent once-over in that area and everything looks to be fine. Plus the exhaust is on the complete opposite side of the t-case from the speedo wires.
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  4. #4 Re: diagnosing speedometer not working 
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    Oh damn you're right, I was thinking of the o2 sensor wires, mine got partially burned after having my old flow master smashed up into the floor boards and breaking the plastic clip holding the wires.

    I do not envy you with this problem. Maybe swap in a 5.3 and have all new wires across the board haha


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  5. #5 Re: diagnosing speedometer not working 
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    Eh, it's been this way for a year already, not the end of the world. I have an old cell phone in a cradle with a GPS speedometer. Only real issue is it doesn't shift into OD, so anything over 55 is kind of a pain, but it's not like my ZJ goes that fast very often anyways.
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  6. #6 Re: diagnosing speedometer not working 
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    Dave, I'm not sure if the BCM has anything to do with the speedometer, but I have a couple of spares if you want to throw one in. I know that the BCM controls the odometer, but I haven't done the research to see if it takes a signal from the sensors before it goes to the actual speedo. Lemme know, I can hook up with you somewhere this week since I'm in town.
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  7. #7 Re: diagnosing speedometer not working 
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    If I remember correctly the wire that delivers speed to the ECM runs up the trans tunnel then splits off and one side goes to the ECM connector and the other I am not sure, I think it was orange and black. I can probably come up with the wiring diagrams if you need them.
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  8. #8 Re: diagnosing speedometer not working 
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    Depends on year of course with the gauge cluster being driven exclusively by the PCM after going to obd2 starting in 96


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  9. #9 Re: diagnosing speedometer not working 
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    95, OBDI.
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  10. #10 Re: diagnosing speedometer not working 
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    Does your cruise control still work when the speedometer doesn't?


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  11. #11 Re: diagnosing speedometer not working 
    Senior Member Lifetime Supporter Jeep Whore's Avatar
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    Dave are you sure that the gear hasn't been ground down? I had moved mine just a little bit thinking it was where it was before and by the end of the weekend my speedo didn't work, I restarted it and the speedo caught and worked for a little until I shut it off again.

    Pull the gear out and just make sure there are no flat spots on it or anything.

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  12. #12 Re: diagnosing speedometer not working 
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    Dave, I have a sensor w/ gear you can have if you want to try swapping in another one.
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  13. #13 Re: diagnosing speedometer not working 
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    Here's a trick I learned off another forum to help you test the speed sensor. Unbolt it and pull the speed sensor out of the back of the TC. Chuck the sensor up in a hand-held drill and with the key on, spin the drill. If the wiring is good to the sensor, it should show up on the speedometer.
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  14. #14 Re: diagnosing speedometer not working 
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    Quote Originally Posted by rradford9 View Post
    Here's a trick I learned off another forum to help you test the speed sensor. Unbolt it and pull the speed sensor out of the back of the TC. Chuck the sensor up in a hand-held drill and with the key on, spin the drill. If the wiring is good to the sensor, it should show up on the speedometer.
    So interesting thing happens when we do this. Yes I'm still fighting this 2 years later lol. The speedo doesn't register anything, however the RPM's go from idle at 750 or so to a touch over 1,000 when spinning the gear in a drill.

    I replaced the sensor and the last part of the pigtail to the sensor, still no speedo. It did kick on for 20-30 seconds the other day driving around on the old sensor, then went back off and didn't come back on.
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  15. #15 Re: diagnosing speedometer not working 
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    Have you tried a new/different sensor? Sounds like the sensor itself has taken a crap and no longer transfers the mechanical motion of the gear to an electrical signal. Simple test for the wiring is to find which pin at the pcm it goes to and check continuity between the pcm and the sensor pigtail. If the wiring tests good, replace the sensor.
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  16. #16 Re: diagnosing speedometer not working 
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    My ZJ used to have a sporadic speedo; I never diagnosed it but always assumed it was in the cluster itself. Cold solder joint or something.
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  17. #17 Re: diagnosing speedometer not working 
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    Quote Originally Posted by Yjsaabman717 View Post
    Have you tried a new/different sensor?
    Quote Originally Posted by BigDaveZJ View Post
    So interesting thing happens when we do this. Yes I'm still fighting this 2 years later lol. The speedo doesn't register anything, however the RPM's go from idle at 750 or so to a touch over 1,000 when spinning the gear in a drill.

    I replaced the sensor and the last part of the pigtail to the sensor, still no speedo. It did kick on for 20-30 seconds the other day driving around on the old sensor, then went back off and didn't come back on.


    Haven't checked the wiring too in depth yet. Really the only PITA with the whole thing is that the tranny doesn't go into OD, and I don't drive it on the highway a whole lot so I haven't put a bunch of time into figuring it out.
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  18. #18 Re: diagnosing speedometer not working 
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    Quote Originally Posted by jsteves View Post
    My ZJ used to have a sporadic speedo; I never diagnosed it but always assumed it was in the cluster itself. Cold solder joint or something.
    I do get a CEL for no input from VSS so I think the cluster may be okay, which is weird because the motor certainly did react to the gear being spun in the drill.
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  19. #19 Re: diagnosing speedometer not working 
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    Well mine still went to OD, so it was a different situation.


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