I have a 2003 F250 ESOF 6.0 diesel and I am trying to troubleshoot and repair the 4WD on it. I have learned a lot from searching here on the forum but I have gotten to the point of seeing if someone out there knows about the GEM codes or the reporting of issues with the GEM. I think the GEM on my truck is bad but I am not certain and I don't like just changing expensive parts out to see if it fixes the problem. I have tried three different OBD2 scanners on my truck to try and pull GEM or the 4x4 DTCs but with different results. None show any Px7xx or Px8xx codes. Two scanners didn't report any codes and one would return a code reflecting a problem with cylinder 5 glow plug circuit so I know that one is at least communicating with the ECU. My question is more on the transmission codes related to the 4x4 and the GEM. Does anyone know if a code or codes would be set if the GEM is actually bad? I am trying to determine if my OBD2 scanners are just not capable of reading these codes or if the GEM is truly bad and would never post a DTC since it is bad. Any help in this area would be greatly appreciated.

BTW, the 4x4 and Low lights do prove out when the vehicle is started and I am not having strange problems like windows not working. The 4x4 and Low lights will not come on nor will the relays click when I switch between 2H, 4H, and 4L. The relays bench test fine and the shift motor sounds like it works when I jumper the relays out.

Thanks in advance for any help.

 

Bump. Still wondering if someone can answer the question, will Px7xx and/or Px8xx DTC code(s) get logged if the GEM is bad?

Thanks for any help.

 

Hi there, I'm having similar problems but with a 2001 7.3 CcLb, the GEM will most likely throw a code. I went and had mine read with a VERY GOOD scan tool, I'd recommend asking around local shops to see if they know anyone with a good body code scanner and have them scan it. Good luck finding a replacement too btw. Ford discontinued the part and it's hard to find. I have threads on my exact problems and as soon as I order a new one I'll let you know if it fixes my problems

 

Thank you for responding to my post and I certainly would be interested in hearing whether it fixes your problems.

I did break down and purchase an iCarsoft i920 specific for my truck which is supposed to read the transmission and 4X4 codes. When I ran it on my F250 there were no transmission or 4X4 codes logged. I did finally locate the GEM on my truck and pulled it out. There was evidence that water had been on a small portion of the circuit board so I am assuming it is bad. I am in the process of looking for a replacement to see if that corrects my problem. It is just strange to me that there were no transmission or 4X4 codes logged. I would think that if the GEM actually controls other functions on the truck it would have posted that the 4X4 system had problems.

 

In 2001 ford stopped use of the GEM modules, and you would need a professional scan tool to read any codes from the transmission on you truck, run of the mill autozone type scanners will not be of any help. but your problem may be within the 4x4 switch on your dashboard.

 

Actually the GEM on my 2003 F250 is labeled "Sport Utility 4X4" with this part number "3C3T-14B205-AB" on a peel off label on the plastic case. Once you open up the case and look at the actual circuit board does it make reference to the word "GEM". It states on the circuit board this: "3C3F-14A608-AB" and "GEM-P131".
The scanner I purchased is not the computer that the dealer uses but it is considered a model that professionals use to read the codes for the transmission and 4X4, or that is what the company stated when I called them to find out which scanner would report the Px7xx and Px8xx codes. It was not a cheap scanner you can buy at AutoZone.

 

Also, the SOF switch in the panel (2H, 4H, 4L) ohms out perfect so I really don't think the switch is the problem.

 

Kind of peculiar that you couldn't get any codes. I also had evidence of water damage having the 2 bottom left (on both block style plugs) terminals having water damage green crusts (sorry I don't know jack ***** about electronics,wiring, or electronic lingo) further making me believe mine had water on it. Now the tricky part is locating gems. I have 2 numbers that I'll try in the next couple of days. One is for a guy in clear water Florida that buys wrecks, and the other is for POWERSTROKEHELP.coms shop hopefully they'll just sell me a part and not make me drive to Georgia to get my truck fixed. I'll let you know if I can track one down.

 

BigBlackF-250 your 2001 does have the GEM module, GEM stand for general electric module. and yes the green crust is corrosion from water damage.
TKrobinson your 2003 uses the CJB (cental junction box) fuse block under your dash, four wheel drive control module (locate in the engine compartment above you A/C airbox on the right side) , Aux Relay box#3 (contains 2 relays), electronic shift on the fly solenoid, DRTS (Digital transmission range sensor) will throw a P07## code, instrument cluster, brake pedal position switch, ABS control module, Data link Connector (obd II port), Four wheel drive switch, USP network, along with fuses# 27, 31, 33, 34, 45, 59.

 

I just wanted to post an update to the 4WD problem I have been having. I finally located a replacement GEM module for my 2003 F250 SD ESOF 6.0 diesel. The GEM was bad and not communicating at all so that answers my questions about whether the system will report a GEM that has failed or not, it does not report it or at least in the failure of the GEM in my truck. I just got through putting in the new GEM and now it is showing going into 4x4 on my dash when I switch to 4x4 High and it will show switching to 4x4 Low. What it is posting as a DTC now is a P1876 code "Transfer case 2-wheel drive solenoid circuit open or short to ground". One other thing I found out when I drove the truck and switched to 4x4 High is that my air conditioner switched from forward vents to the defroster, so I may have a leak in the vacuum hoses going to the front hubs or bad front hubs. Now I have to start researching the DTC problem but I actually feel that I am now making progress.

So many do not give updates when they start making progress so that is why I wanted to give an update.

 

Another update. I was able to determine that the PVH solenoid was bad by plugging the output of the PVH solenoid and there was no change to the air vents switching to defroster. I received the replacement PVH today and installed it which corrected the air vent switching to defroster and removed the P1876 code, and the real test....my 4x4 also switched and locked both hubs!!