All the instruments in the cluster work (tachometer, oil pressure, coolant temperature, &c) except the speedometer and the odometer. The technician at Joe’s Garage determined that the cable is getting 5v at each end–it’s grounded and getting power. This leads him to conclude that the speedometer cable is not the problem, nor the sensor. Instead, he’s diagnosed the instrument cluster as a whole.
Does this seem plausible? I’d think the sensor would be a more likely culprit, and an easier fix.
Usually when the speedometer/odometer stop working there’s a problem with the instrument cluster.
If there were a problem with the vehicle Speed Sensor the Check Engine light would come on with a code indicating so.
Tester
isn t this a mechanical speedo?
It’s digital to the best of my knowledge (1996-2001), but aren’t there still pinion gears and the like in there that may get damaged without firing off the idiot light?
The instrument clusters are interchangeable from 1991-1996 and are completely electronic.
http://jeepin.com/features/gaugeswap
There’s a driver in the instrument cluster that fails where it doesn’t operate the speedometer/odometer. And that’s why the instrument cluster has to be replaced.
Tester
If in doubt you can view the speed sensor input in the PCM with a scan tool. The cruise control won’t work if the speed sensor fails. If your cruise control is working the speed sensor is working.
Some of the later Cherokees had a corrosion problem with the instrument cluster connector.
OK, thanks everyone for straightening me out.
If it were me, I’d have that speed sensor looked at again on the offchance the circuitry in it is bad or there is an issue with the sensor not rotating. I’m not familiar with this particular transmission but many use a plastic drive gear and sometimes those have been known to shear off.
For what it’s worth anyway, about 2 years ago the speed sensor on my Lincoln died while I was out on the open road and this led to no speedometer, no cruise control, and no overdrive function.
There were no codes set and no CEL illuminated.
At home the speed sensor was shown by the VOM to be stone dead and since I still have my wrecked Lincoln I just yanked the used one off and swapped it out; about a 10 minute job altogether. Problem solved.
I took your advice. Here’s what a borrowed code scanner told me. I’m not clear on what “pending” means for this scanner, but I do think the VSS is more likely than the cluster at this point.
Should have asked earlier: Is replacing the VSS something an idiot (me) can plausibly do in his driveway? It looks like it’s just one bolt, plug-and-play so long as the little plastic wheel is unharmed.
I’d rather gamble $25 on a VSS than deal with the cluster first.
Thanks.
There is no plastic gear on the vehicle speed sensor.
It’s an electronic component.
Tester
My point about the plastic gear is not about one in or on the speed sensor; it involves a drive gear in the transmission like this one.
As I’ve stated on this forum in the past, I’m not a Jeep guy and if I’m wrong I’m wrong. My bad.
My assumption was that the speed sensor is like this one.
It depends on which transmission this vehicle has. The AW4 is the most common and has a sensor with no gear but not the same as the Chrysler sensor shown.
I don’t believe that scan tool will display live data so you can’t view the speed sensor input as you drive. If the fault (pending) was set by someone unplugging the sensor for testing the fault is invalid. Clear the fault and see if it returns.
This vehicle must not have cruise control, there has been no comment if it has stopped working.
This truck has the AX-15 manual transmission. The speed sensor plugs into the NP231 transfer case, which is also giving me trouble. No cruise control. I’d get under there to take more pictures, but the rain is fierce today and I have to work in the driveway.
Also, the technician had unplugged the sensor for testing. In doing the testing, he finally drained the battery (it was on the way out anyway). I plugged the sensor in and replaced the battery before scanning for code.
As I stated, I’m not a Jeep (or Chrysler for that matter) guy at all but I would think a transmission speed sensor on this vehicle should be similar to those on other cars with a drive gear spinning a driven gear on the sensor. Plastic may not be the operative word with nylon being a better one.
Page 21-63 shows a speedometer drive gear on the AX-15. What it drives I cannot say with certainty but I assume it rotates a sensor. Granted, this is a 2WD model but one assumes a 4WD would operate on the same principle.
Just theorizing; maybe I’m dead wrong.
The VSS is as you describe it, ok4450–but it’s in the transfer case, not in the transmission, on this vehicle. A nylon wheel on the case rotates a metal spindle in the sensor, which plugs into an electronic harness and on up to the computer.
The code indicating a bad VSS was cleared out–the computer is currently reading no codes at all.
I figured that I already own a used instrument panel, so I might as well start where I have. So today I pulled the instrument panel, cleaned all the contacts, tightened all the screws that had come loose over the years, put it all back and found no change: all the instruments except the speedometer and odometer work.
Next thing I suppose is to get someone else’s used instrument panel and try again.
OK, so I drove around for a while and the VSS code came back. Got some help replacing that (had to wire in a new harness too, which is well above my paygrade). Now it works.
Resolved. It was the sensor.
Thanks for letting us know!