Hey everyone. Lookin for some insight on the issue i am having. My ranger's abs light comes on and off, and the speedometer will spike up and down when driving. Then it almost "bucks" like its dying out for a split second then comes back on. I put a new wheel speed sensor on a while ago, so im not sure where to start.

 

1999 Ranger has an ABS sensor on the rear axle differential, is this the one you changed?

From 1998 to 2000 Ford used this ABS sensor for the speedometer and computer speed signal
Its 2 wires run to ABS module but are spliced into and run to the GEM module behind the radio
The GEM module converts the ABS sensor signal to a speedometer signal, and then it goes out to the speedometer, computer and cruise, if so equipped

The Rear ABS sensor was a common failure in these years
And if its failing ABS light will come on and speedometer will be erratic

 

Yes this is the one i changed, even threw some dielectric grease in the connector. But this issue isnt frequent. I had a previous encounter where it was completely dead, and had it jumped to get me to work from school, where it did the same thing, ABS light on and bucked and shook while driving, then when i got it home and threw it on the charger to start, i started it and it smoked from the radio. I lost dome light, wipers, and door chime in the process, and popped 2 fuses (One had to do with the GEM module). If i remeber correctly 24 and 26 were popped...

 

Yes, you had a short at the GEM module, behind the radio, you will have to pull out radio and have a look

This was probably draining the battery.
But a low or weak battery wouldn't be the cause, it would be the result of a short.

My guess is that the GEM module will be damaged, as said the Rear ABS sensor wires are connected to both the ABS Module and the GEM
These 2 wires would have to be shorted at/in the GEM for it to effect ABS module

This shouldn't effect the engine though, GEM or ABS has nothing to do with engine "bucking", so there is more to this electrical issue

 

Forgot to mention i did take the radio out, and had a spare GEM from the junkyard handy, but the old motherboard didnt have any black burn marks or melting, so i kept it, and i replaced the 2 fuses that popped, which gave me wipers and all that back.However there was a relay in the engine fuse compartment in which seemed to get hot and upon inspection was corroded, perhaps the metal "flapper" was sticking and thats why it died that day. But i will have to take another look, i have the GEM wiring diagram here somewhere so maybe theres a bare wire inbetween the GEM / Wheel speed sensor.

 

So it died on me again and i jumped it to get home, abs on and spedo erratic. As im charging it at home i key on, and the pcm relay is buzzing. I leave it alone for a bit, tossed in my new GEM, and then tried for another start. Still dead. So i go to engine start and key on, this time buzzing from the back. I go back and slide under my truck and hear buzzing from the fuel pump... to add on previous owner spliced all of the radio wires for this touch screen kenwood radio... I would greatly appriciate any tips / help.

 

Use a Volt meter and test Battery voltage key off
A good battery will show:
12.8v when new
12.5v when 3 years old
12.3v when 5/6 years old
12.2v or lower is a failing battery

Then test battery voltage engine running
14.5v-14.9v at startup
13.5v-13.8v after 5 minutes or longer of engine running

Alternator takes over powering all the vehicle electrics after startup, it also keeps battery charged up for next startup
If its not outputting at least 1volt above battery voltage then engine will die trying to run off battery voltage

Could just be a blown fuse, does the Battery Light come ON when key is turned on?
If it doesn't come on check fuse #15 in cab fuse box, 15amp
This is the ON/OFF switch for alternator

 

Positive battery cable was corroded so i replaced each end and cleaned the terminals and wires with baking soda. That gave me juice back, and fixed the issue of my battery drain (i hope). But now im stuck with no wipers, dome light door chime (not worried about this one), and then suddenly VSS code showed up. No check engine light, just the ABS light. So i hooked up my little cheap ford tuner /scan tool and it gave me P0503 (Erattic / Inoperative Speedometer or VSS). Im thinking this will all link in with the GEM but i replaced it with a junkyard one which could also be faulty, but im not sure. Im using pro demand to help me test continuity and such to my GEM. Not sure what to do at this point. Fuses and relays all check out fine, except for 24 and 28 fuse sockets in cabin which have no juice at all. Fuses are fine, but no juice even inside the socket. 24 is Clutch Pedal Position switch, Starter interrupt, and Anti-Theft but all of these operate as the truck starts fine, and anti theft goes off. 28 is my GEM and radio.

 

Does Battery Light come on with the key and then go off after engine starts?

P0503 is detected by the computer having an erratic signal
And yes the GEM controls ALL cab electrics except headlights and parking lights

But ABS light means ABS module is having a problem as well, speed sensor signal for ABS doesn't come from GEM, its direct to the ABS module
Having P0503 AND ABS light would point at rear axle ABS sensor or wiring issue, not the GEM