When truck is started, a self-test is performed.

If that self-test fails......system is disabled.

There should be code for what failed in pcm.

Trying to troubleshoot a disabled system will be.. misleading

It's frequently the shift motor.......

 

I have a 97 wherein the 4WD quit functioning. No dash lights illuminated, no click behind the dash, no power to any of the controllers. Since the on the go system is computer controlled, after much tracing down the problem to no avail, it occurred to me to disconnect the battery. upon reconnecting and starting the vehicle the indicator 4x4 light came on, but moving the switch to 4H did not turn it off. turning off the engine and restarting it once more I was able via the switch to put it back in 4H and the light went out. After driving it a bit. I tried the system again and it now works perfectly.
Earlier, I had had a problem disengaging the 4WD while backing. Apparently the GEM did not like that and disabled the system. I have not read of this remedy anywhere but it worked for me.

 

You probably have an intermittent problem that is quite likely to reappear sometime in the future. That's just the way that these things usually go. You just cleared a code and it passed the test this time.

 

Hey guys first time on here I've been trying to fix the 4x4 in my 2001 f-150. Little back story i have already replaced the switch and repaired vacuum lines and a new vacuum reservoir and i have come to find out i have no ground to my solenoid does that mean i need a new gem module or is there something else i can look at. But if it is a gem module do i have to take it to a dealership or could i do it.

 

Same problem, no ground on my 4wd solenoid. Don’t know what to do next? There’s a clicking in dash when I switch to 4H but light on dash never comes on and no ground on 4wd solenoid. Not sure what to check next?

 

This is very similar to the problem I am having with a 2000 4x4. The truck will not move out of 2wd.
I found a YouTube video that explains how to do an in-depth diagnostic.
Test 1) I have tested for resistance in all 3 positions of the switch. Result - All three positions are within specs.
Test 2) I tested for power at the switch connector plug using the second pin from the left (blue wire, should be +) and the 4th from the left (black wire, should be -) Result - no power.
Test 3) I tested both solenoids for positive power at the connector. Result - both have positive power.
Test 4) I tested both solenoid connectors for ground in all three switch positions. Result - 2wd solenoid gets a ground. 4wd gets no ground at any switch position.
Test 5) Checked to see if both solenoids get constant vacuum from their supply lines (bottom one if I recall) Result - both solenoids are getting engine vacuum.
Test 6) Using a vacuum pump I tested both vacuum lines going to the front differential diaphragm. Result - both hold a steady 20 inches without leaks.
Test 7) I checked the 10amp fuse at position 23 in the cab under the GEM. Result - It has NOT blown.
Test 8) I checked the 30Amp Maxi fuse in the engine compartment fuse box at position 104. Result - The fuse has NOT blown; current is active at the two pins.

I did not know to check fuse 17 and will do that tomorrow. Is this the power circuit for switch power?
And
It could be GEM damage, In the past, I have seen a few drops of water drop out of the driver window pillar.

Anyway, if anyone can offer suggestions as to where to look next the help would be welcomed.

 

IN MY 2000 f-150 4wd there is no fuse 17 in either fuse box. Owners manual shows both as not used.

 

On my 2002 F150 super crew it was a bad transfer case shift relay module F85B 14B 194CA was intermittently working. It located to the right of the instrument cluster. There is a video on YouTube that has you remove the cluster. I changed mine by removing the top of dash (bubble). It has maybe 10 7mm bolts & then it pulls towards the steering wheel. Only issue is the module is discontinued & only available used on eBay or a salvage yard. I went & picked up a couple extras at the yard.

 

I know when I had a bad GEM due to water intrusion I had a host of other issues as well. This was one problem so it sounds like water wasn’t the issue.

 

I bought my 1997 f150 4.6 Lariat XLT 4x4 new.. Has about 300,000 miles in it..Been a unbelievable truck, with No major issues just maintenance..Just great!.. But I have had issues/problems with the 4x4 engaging/disengaging, sometimes works great other times not,, I rarely use it (truck) much anymore, No one has worked on my truck but me.. BTW.....I'm a 67 year old ex electronic engineer..and also a business of restoring classic muscle cars ( special,specifically 70-72 Pontiac GTO's for around 25 years ( own a full shop)..This issue has been going on for a few years..Some times it will work.. but rarely now..If I disconnect battery and short the ends it will "reset" the system ( GEM) I assume and work again.. sometimes not but usually does..LOL All the hardware is operating , only when it feels like it though..After a "reset" usually works.. SOO.. I assume there is a issue with the Gem.. maybe capacitance/transistors other components in the GEM.. are weak? no other issues with the truck, electrical OR mechanical..Don't see ANY water intrusion also.. Anybody else familiar with this? Also to mention, I completely restored the interior ( leather/grey) and my red truck looks almost new! Thanx for any help opinions,,