Electrical Gremlins (Trans, Speedo, Wipers, Lights) GEM worthless?

[Still Bill]

Hello. I originally posted this as as Transmission problem in other section (http://www.therangerstation.com/forums/showthread.php?t=176201), but now I think it is more of a general electrical problem.

1998 Ranger 2.5L automatic, no power accessories.

Occasionally and randomly, something happens that affects all the following. It happens once or twice per week, and lasts from 2 hours to overnight. Truck runs great most of the time. No warning lights. Everything works. Newly rebuilt transmission.

SYMPTOMS (all happen at once):

Transmission won't shift above 2nd gear.
Speedometer doesn't work.
Dome light (overhead interior) does not work.
Wipers do not work.
Overdrive light blinks.

Speed sensor at axle is new. Transmission connections and wiring are new. Everything obvious has been checked, including grounds (if we found them all).

We tried replacing GEM with new (used) unit. No difference (still random, same problems).

Today, I disconnected the GEM just for kicks. This was done while the truck was in "Perfect mode." I was shocked to find that EVERYTHING, and I mean Everything, sill worked normally. The only exception I found was that the ABS light did not come on when key was first turned-on. Wipers, lights, horn, AC, brakes - all perfect. We drove 50 miles.

One more thing. It is my son's truck. While driving today with GEM disconnected, he noticed that the speedo was reading 72. I'm sure it was accurate. But, he said that ever since we had the truck (4 months) the speedo would always max-out at 65. I never knew this, and can't swear it's true, but seems plausible.

Can't say of problem is fixed - every time we think that, it comes back a few days later at random. Why have a GEM that doesn't do anything?

Anyone have any insights?

PS: I just received in the US Mail the Conplete 1998 Ranger "Electrical Vacuum and Troubleshooting Manual". Hard copy, brand new. This beast is about 250 pages, and 200 of tham are wiring diagrams. If anyone needs copies of certain pages, let me know.

 

[RonD]

You did not unplug the GEM if speedometer, wipers and interior lights work.

Not sure what you unplugged?

 

[adsm08]

If this is a RABS only truck it may have been the ABS module that was unplugged. On the RABS vehicles the electronic control portion of the ABS module is mounted inside the cab, rather than directly to the HCU under the hood.

IIRC the VSS signal from the rear axle sensor runs directly to the ABS module and the PCM. The signal for the speedometer is run through the ABS module, but if there is a failure (Like the module being unplugged) then the PCM's copy can be substituted via the CAN.

That would account for the lack of prove-out of the ABS light, and why the speedometer would suddenly start working differently.

 

[Still Bill]

This is what I unplugged (behind radio, to right):

adsm08: Thanks for the explanation, but you lost me with the acronyms. Is the speed signal for the speedo the same signal that the tranny uses for shifting?

Any idea if this is what is causing the group of symptoms, or other ideas? Vehicle still working fine today (for now). Fingers crossed. Black box in photo is still unplugged.

What is the other electric box behind the radio (to the left side)?

 

[RonD]

adsm08 picked it, that IS the ABS module.

Ford part number is 2C018 which is ABS module

F59F-2C018-AA

Center number is what part is/does, and that number would be the same for any ABS module in ANY Ford vehicle, the front 4 numbers tell you what model

14B205 = Ford GEM module, again for any model Ford, car or truck

 

[Still Bill]

Stopped working again today!

Seems I have be mis-informed by several different people. I was told the GEM and ABS were the same unit. I am encouraged now, because maybe the GEM is still my problem. Does this make sense?

To refresh, all this happens at the same time, randomly, perhaps more frequently when the weather is hot:

tranny won't shift above 2nd
Dome light won't work
Speedo is dead
Wipers are dead
O/D light flashes

Lasts about 8 hours, then starts working again, usually in the evening.

I will try a new (used) GEM as soon as I find out where it is, so I can get the part number (truck not here right now).

 

[RonD]

Transmission not shifting and OD Flashing could/would be related to speedometer signal being lost

These would be directly related to GEM
Dome light won't work
Speedo is dead <<< signal to computer would also be dead
Wipers are dead


GEM is behind the radio same as ABS module

 

[Still Bill]

Found it!! 100% sure.

So, that was the ABS module I changed previously. Located the GEM on my vehicle. I have all the wiring diagrams. I realized there were some other functions that the GEM also controls on my vehicle, including seatbelt unfastened warning, door ajar light, and key left in ignition chime. We never noticed if those were also affected.

My son said he thought it happened when it was hot (not engine temp, but weather). This explains why more frequent lately.

So, since GEM is next to heater vent, I turned up heater and propped GEM t in front of blowing hot air. Came back 20 minutes later and everything was off (including things like chime that we never noticed before). I verified that GEM was getting voltage from the various hot feeds.

Then, I took GEM into house and put in freezer for 5 minutes - plugged back in and everything works! Took GEM out of its plastic case and held in front of heater - heard an audible click when it shut off 15 seconds later. Disconnected it and waved in air for 30 seconds, plugged back in and it works!

Pretty definite diagnosis, I think!

Thanks to everyone who helped!

 

[adsm08]

I'd agree, GEM is the issue.

 

[Still Bill]

Well, just received a NEW GEM purchased off ebay. Plugged it in, and it sucks! Engine starts OK, but as soon as you start moving, the speedo goes full scale, and the truck barely runs. SIGH! Endless nightmare!

 

[Still Bill]

So, Three different Ford dealer service departments tell me that a NEW 1998 GEM has to be programed to work. Waiting for a cheap used unit from eBay, to see if that might work, but not sure if it has to have all the same options. Otherwise, I will spring for the $129 to program the new unit.

 

[adsm08]

Yes, a new module will ship blank and has to be programmed to the proper vehicle configuration.

 

[Still Bill]

FINALLY! Seems to be fixed! Used unit from eBay for $40 delivered.

Took a gamble - advertised as no power windows or alarm (like mine), BUT from a Manual Transmission vehicle. Mine is Automatic - but seems to work fine. Still need to check if speedo is reading correct (seems to work).

 

[Still Bill]

One week, no issues.

 

[Still Bill]

One month. Running great.

Speedo is inaccurate over 60 mph though.