Hi all, I have a weird something going on with my GEM module (affects transmission shifting, dome lights, etc.). The transmission goes into limp mode, which indicates no signal from the VSS and/or GEM module. I changed the VSS and confirmed I have voltage at fuses 10, 25 & 26.

When I unplug the GEM module and plug it back in, the dome lights (indicator system is working when the doors are open) stays on for a few seconds, then there is a click and they go out.

Thought this would be the battery saver relay, which I believe is the one behind the glove box, so I bypassed that and the click still happens with the same result.

The only other thing in the region of the noise is the anti-theft box.

Any thoughts on what is going on? Or is there a work-around where I can provide direct voltage to a wire in the GEM and get the trans working again?

 

What YEAR Ranger?

Computer and trans ONLY needed GEM in 1998-2000 Ranger, and just for speed signal

 

1999 Ranger 3.0, 2WD, Flex-fuel

 

For 1998-2000 Rangers:

If the ABS light is working, comes on with key on then goes off(bulb test), but is not on when driving, then rear axle VSS is working fine, not the problem

There is a red/pink wire on GEM pin 9(VSS IN), that comes from/is spliced to, the red/pink wire on VSS that runs to ABS module
You could do a continuity test from VSS wire to GEM wire, maybe the GEM wire is broken

On GEM Pin 1 is a grey/black wire, this is VSS OUT, it sends out the "corrected" speed signal to speedo/odo, computer and cruise, grey/black wire just splits and runs to all 3 units
You could do a continuity test from GEM wire to computer wire pin 58

Speed correction circuit is a separate circuit inside the GEM and rarely fails, but any thing is possible
Any other issues with the GEM would most likely be unrelated

Fuse 10, 20 and 25 in cab fuse box powers the GEM
There are no relays on these fuses, so if fuses are OK then GEM is getting power

GEM Controls the battery saver relay but doesn't get power from it
There is an interior light relay as well as battery saver relay

 

Wow, what an excellent answer! So looks like the dome light issue is separate from the trans. issue.

Do you think splicing the Pin 9 wire and Pin 1 wire together (bypassing the GEM) would work (just to get shifting back temporarily)? Sounds like the GEM just corrects for tire size, etc.

 

I should have also mentioned that the cruise control, wipers, and who knows what else do not work also.

 

Cruise is not part of GEM, wipers are
Cruise does need Speed signal from GEM

No, there is no way to "by-pass" the speed conversion
The Rear axle VSS sends out a 20,000PPM, pulses per mile, signal for the ABS system

The Ford speedometer, computer and cruise, need an 8,000PPM signal to work, that's what the older speedometer gear setup used, 8,000PPM, that gear/VSS was removed in 1998(and up) Rangers, so Ford need another speed sensor, they chose the Rear ABS sensor and add the 20,000 to 8,000 Conversion circuit to GEM

In 2001(and up) Ford added an OSS(output shaft speed) sensor back onto the transmission, I think its about 25,000ppm
OSS is hooked directly to computer and computer does the Conversion, 25,000ppm to 8,000ppm, and sends it out to the speedo, and cruise, computer already has it, lol

If wipers and interior lights are not working them most likely GEM issue
You need a 1999 GEM that matches YOUR vehicle, Power windows/locks or no, 2wd or 4x4, those are the only 2 things that need to match

 

Just thought I'd post an update - turned out it was the GEM. Bought a used one off Ebay, installed in 10 minutes, and back in business. Thanks!

Everything works again, including the cruise control (cruise is a part of the GEM by default - if the VSS signal is not getting through, the cruise cannot work as it has no idea how fast you are traveling.

 

Good work

Thank for the update and THE FIX

Yes, I said that
"Cruise is not part of GEM, wipers are
Cruise does need Speed signal from GEM"