GEM module questions! - Ranger-Forums - The Ultimate Ford Ranger Resource


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  #1  
Old 1 Week Ago
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GEM module questions!

Hey guys quick question about the Speedo and GEM module. I'm trying to look at wiring diagrams to help troubleshoot my intermittent Speedo/ODO issues. It looks like the PCM is what calculates speed? And I pulled my GEM apart and looked at pin 9 and it looks to lead to nowhere. So does this mean that the Speedo isn't necessary at the GEM because I don't have cruise control? It's a standard transmission.


I can hook up a reader to the truck and get vehicle speed all day even when the physical gauge doesn't work. So the vss is working and the pcm is getting the signal. I'm thinking solder joints in the cluster maybe.

any help is appreciated. Thanks guys!
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Welcome to the forum

What year is your Ranger?
Really matters on this question

1995 and up use electric speedometer
1995-1997 used a speed sensor(VSS) on transmission or transfer case, which ran directly to electric speedometer/odometer, signal was shared with Computer, GEM and cruise

1998-2000 used the VSS for ABS system located on rear axle, VSS signal(20,000PPM) ran to the ABS and GEM modules, GEM converted signal to 8,000PPM signal the speedometer uses
GEM's speed signal OUT was sent to computer and cruise, along with speedometer during these years, so if computer was getting speed signal then skip the GEM, its working and look at the instrument cluster.
Look for the grey/black stripe wire

Yes pin 9 Grey/black stripe wire was used for GEM's VSS IN
Pin 1 was used for VSS OUT, also a grey/black wire, it ran to speedometer, computer and cruise in 1998 to 2000

4 wheel ABS modules were used instead of the GEM for the conversion between 1998 and 2000, but most Rangers had only Rear ABS so used the GEM

2001 and up used OSS(output shaft speed) sensor that ran to the computer(PCM) which converted it to the 8,000PPM used by speedometer

VSS and OSS sensors generate their own AC Voltage when they are active, .5 to 2.5v AC depending on speed of tone wheel they are using

Last edited by RonD; 1 Week Ago at 12:03 PM.
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Hey Ron! Thanks for the response.

So it's a 1996. It's got the vss in the tailshaft. So far I know it works and it's intermittent and goes bad when warm. But always have speed on my reader.Even been a few times where I slapped the dash and it worked for a couple seconds.
I decided to disassemble the cluster and really didn't expect everything on the speedo/tach pcb.
I've got power but unsure of the signal. I'm wondering if the little snap in clips that the gauges lock onto have ever been the culprit. I want to say it's a heat issue. But I just dont know. Anythingnon the gauge's pcb that you've known to go bad?
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1996 Ranger wouldn't use GEM for speed calibration

VSS on tail shaft wiring runs directly to the Cluster, Computer, GEM and cruise

This is the VSS: http://www.therangerstation.com/tech.../vss_test1.JPG

It generates its own AC voltage when spinning, but there is a + and -
The system only use 1/2 the signal, AC voltage is a wave, a sine wave, each wire pulses above and below 0 volts, so 1 wire is assigned as -, a ground, the other wire is +, and is used for the MPH pulse

1995-1997 VSS wiring diagram here: http://ww2.justanswer.com/uploads/FO..._172049_a1.jpg

You can see the Pink/orange wire is Grounded at bottom of diagram, making the Grey/black wire the +, the signal wire
Computer and cruise both have specific ground wires for the VSS, GEM and Speedometer do not, so use their local ground as the other side of this pulse circuit

See instrument cluster wiring diagram below
Connector C215 pin 1 is the grey wire with the pulse speed signal
C215 pin 2 is the local Ground for the speedometer, but several other gauges share that Ground, so if it was loose I would expect other gauge to be acting up.

Yes, while not at all common, instrument cluster traces and connections can go bad
Attached Files
File Type: pdf 1996 instrument.pdf (87.2 KB, 3 views)
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Dude I see you responding to so many people. Thank you for sharing all this knowledge.

so last night I had it all apart. (Put in a new stereo.) While checking the instrument cluster, I had continuity issues with the trace from the speed sensor wire to the speedometer "peg in that spring connector. I've done lots of continuity checks before, worked on pcb, mostly home wiring (electricians don't like to wire 3-way switches correctlyhaha)

Anyway, the trace wasn't blown or anything and just magically, I had continuity. It was weird but it was late and I was tired. So I reinstalled it and noticed pin 1 on the connector was a little lower than the rest. So I fixed that, grabbed the wife to check out the stereo and took it from a drive. this is around 9:30 pm. NO SPEEDOMETER. Damn. So we go home. Decided to throw my new shocks on so by 10 pm I test drove it and the SPEEDOMETER WORKED! So I just dont know. I don't drive it everyday but I need to taleitout today to grab a toolbox so I will see.

would it be smart to say it has nothing to do with the dash? I'm lost man
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Speedometer and odometer share the same speed signal BUT.............they use different motors, so if BOTH quit at the same time I would suspect the signal wire to the cluster, if odometer continues to move then problem is in the cluster
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