Hey guys, my 98 Ranger (3.0L automatic, 4x2) has not had a functioning speedometer for awhile now. Im used to just using the tach, but I finally want to get this fixed if possible. I have replaced the speed sensor in the rear diff housing twice (once with a NAPA part - which made the transmission lose its mind, and once with a FORD part). Neither of those fixed the issue. The trans shifts fine now, and every once in a while, on a cold start up, my speedo will function for a few minutes - then just drop to Zero. I have removed the instrument cluster and shipped it to a testing house - only to be called and told that it worked fine for them. Can any of you experts out there tell me what other systems or sensors are used to input speed signal to the cluster? Im not an auto mechanic by trade (I built jet engines for research), but I know my way around a tool box and a DMM. I have also perused this forum for awhile and have not found a direct solution (so my apologies if this is here somewhere in the vastness of Ranger-Forum)

So, anyone else have this issue and been able to fix it? If so, how?

Thanks

 

Welcome to the forum

1998-2000 Ranger did use the ABS rear axle sensor for speedometer, computer and cruise control, but not directly

The ABS sensor sends out about 20,000ppm(pulses per mile), Ford speedometer, computer and cruise control need 8,000ppm
So in 1998 to 2000 the GEM module(behind radio) was used to convert the 20,000ppm to 8,000ppm

If rear axle sensor should fail the speedometer would quit working AND.............ABS light would also come on, so no ABS light means rear axle sensor is working(assuming ABS light works, lol)

The computer also needs the 8,000ppm signal, as does cruise, but the computer will set a P0500 code(no speed signal) and turn on the CEL(Check engine light) if the GEM wasn't working and sending out the 8,000ppm signal

So GEM appears to be working if there were no codes set

That leaves the speedometer itself OR the wire from GEM to speedometer

Speed signal is on a grey/black stripe wire, it comes out of GEM then has a splice(not sure where) where it splits and runs to speedometer, computer and cruise control
Same color grey/black wire at all locations

Cluster diagram below
There are 3 connectors, 16pin, 12pin and 10pin
Speed signal is pin 1 of the 12pin, grey black wire

GEM module will also have speed OUT on pin 1 a grey/black wire

You can test continuity between these two wires and splice in a new wire if there is an issue

The speed signals are AC voltage, but just for the pulse above 0volts, voltage is not used frequency is, so only 1 wire is needed and the common ground of vehicle
So you could test AC voltage on the grey/black wires if you jack up rear wheels and put it in gear and spin them, 0.5vAC to about 6vAC(70mph) would be seen on any of the grey/black wires

In Explorers Ford used the 4 wheel ABS unit for speed conversion, not the GEM, the cluster diagram has both methods shown

 

Thank you so much for this detailed explanation. I had heard long ago that the GEM can cause some of these issues, but I had forgotten until your post. I do now have a sustained (used to be intermittent) CEL, but NO ABS light. So I will follow your ideas on this and see what I can get done!

Thanks again!