Hey all i've had the ABS light on for a couple months now and have yet to find someone w/ the proper scanner to read the codes but will have it hopefully cleared soon as my buddy says he has access to one now.

Anyway i went snowboarding for the first time this winter and went to click into 4WD (hi) and NOTHING :santa:

No audible click from a relay and no 4WD green light on the dash

I do believe i checked all the under-hood fuses but are there more i'm missing say under the dash that i may have overlooked?

I'm wondering if the fact that the ABS light is on that it won't let me engage the 4WD due to a "safety" type issue.

Can anyone shed some light on this issue?

Sory if it's a very common thing to happen but i'm limited right now on time to search the sight as i may need the 4WD over the New Years holiday :o

Thanks and have a safe and HAPPY NEW YEAR!

 

You could be on to something. The 4x4 relays and the ABS system share a common fuse. #23 10 amp in the Passenger Compartment Fuse Panel. But if it was blown your Hazard Flashers would not work. Have a loot and let us know.

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Thanks for the response and i apologize for not having more diagnostic info to share but i haven't had much time to run tests.

I did check all under hood and under dash fuses and all are good.

My next step will be to check the continuity of the 4WD selector switch but it does show visible light from the cluster so i assume it has power.

After that i would assume the next train of thought would be to check the GEM module as best i can and if not or at the same time i guess from research also will be looking at the vaccum actuated motor on the TC.

I'm just trying to rule out all possibilities that i have read about after finally being able to search thoroughly on the site.

I don't think i've had water contamination in that kick panel are to have the GEM go out so i'm not sure why it would but i guess it seems to be a common issue on these truck like many.

 

The dash switch has three resistors and a light. The light is powered by the parking light circuit. The three resistors are tied to the GEM so it knows what position you want to put the transfer case in.

In a nutshell: The switch tells the GEM to change the transfer case position. The GEM then activates relays to do so. It first engages the clutch in the T-case via a relay which spins up the front driveshaft. It then activates an electric motor that moves the shift forks in the transfer case. There are contact plates in the motor assembly that tell the GEM the position of the shift forks in the transfer case so it knows when to stop powering the shift motor. It finally activates/deactivates the vacuum solenoids on the firewall that control front axle shift motor to lock or unlock the front axle. A corroded wire, faulty relay, faulty switch, shorted or open circuit, blown fuse or faulty GEM can cause the transfer case to not engage. FWIW 99% of the time a faulty shift motor assembly on the transfer case it the cause.

Regards

Jean Marc Chartier

 

Thanks once again for your input Jean Marc.

I will be digging into things tomorrow but i was just trying to rationalize things and since you said that the GEM will activate the relay (which i assume is what i normally hear clicking when it was working normally) i hear nothing.

To me this leads me to believe it more a problem w/ the GEM but as you stated that it's 99% of the time the shift motor.

Am i wrong in this assumption due to the necessity of the shift motor working to allow the electrical path to flow properly to illuminate the light on the dash?

The thing is that even w/ the selector switch on 4WD it does not feel like it even engages the vacc solenoids to lock everything up.......again why i feel it's more GEM related that the shift motor but i'm probably way wrong lol.

 

When you command 4x4 it is the GEM that controls the front axle vacuum actuator motor solenoids. The front Axle lock up is the last function that the GEM performs so if the GEM doesn't see a signal that the 4x4 is engaged it won't lock the front axle.

In sequence of events. You turn switch to 4H. The Gem sees the command and activates the electric clutch in the transfer case. This pre engages the gears and spins up the front driveshaft so it matches the speed of the rear axle. The Gem Turns the Shift Motor on so it can move the shift forks in the transfercase. As the shift motor turns the contact plates, 4 of them, change alignment and that opens and closes circuits to tell the GEM that the shift has occurred. If the circuits do not correspond to what they should the GEM will not lock the front axle. What usually happens is that the motor jams and then GEM does nothing. If the contact plates fall in between settings the GEM will set a code for the incorrect plate alignment.

The manual t-case is much simpler. You pull the lever the GEM energized the clutch the forks move and the front axle is engaged.

Regards

Jean Marc Chartier

 

Again i thank you for reiterating the info and i'm very clear now on the logistics of the operation.

I will today take look at the shift motor on the TC and will report back w/ what i come up with.

Also just to rule out the switch i'm going to test the resistance in each mode (2wd, 4wd hi, and 4wd lo.

Sorry for the ignorant ? but should i be testing the switch w/ it unplugged from the harness on the 4 pins on the back or or should it be connected with me poking through the wires to test?

I think i stumbled across the specific ohm values for each position in another thread i saved but if you happen to know them for it would be great to be sure they are correct.

I will also try and manually move it into 4wd at the shift motor/tc as it was explained also in another thread.

Regards to you as well JMC

Patrick

 

In 2wd the resistance is 4100 to 3700 ohms. In 4hi the resistance is 1150 to 1050 ohms and in 2Lo it is 380 to 340 ohms. You probe the 2 middle contacts of the switch so it has to be disconnected. To get to the switch you need to remove the trim the surrounds the radio and heater/AC controls. A finger nail between the trim and the instrument panel and pull it off. Four snaps hold it in place. Don't worry it will not break when you pry it off. Once the trim is off the switch connector is accessible.
Note Just to be safe I would recommend you disconnect the battery because the Air Bag switch is in that trim piece. This will allow you to safely disconnect the air bag switch and bring the trim piece to your work station to test it.

Regards

Jean Marc Chartier

 

JMC,

Got a chance to finally check the switch out and it seems that the resistance in all positions is w/in spec.

I will now get underneath and check out the shift motor on the TC.

Will let ya know what i find out.

 

Update:

So i went under the truck and did a couple things and here's what i found:

1 - I sprayed the connections to the electronic switch on the TC w/ electronics cleaner and let dry.

2 - I removed the shift motor from the TC and had a buddy jump in and switch the in dash switch to se what happens.

After re-plugging the shift motor at the harness my buddy said that it shifted into 4wd hi and it illuminated the dash light. WOOHOO! Then he shifted it back over to 2WD and it went back and the light went off. WOOHOO again.

Then he tried to go back into 4WD and NOTHIN!

So i had him turn off the truck and un-plugged the switch at the harness and then re-plugged it and had my buddy try again.

It did the exact same thing......worked once and then not again???

What are you thoughts?

Is it more likely the motor itself like you said it most probably was or do i need to further investigate elswhere?

Called the local Ford dealership and they want $281.65 special ordered.

I sure hope this pinpoints the issue and i'm once again very tahnkful for your help and guidance! I owe ya a nice cold one!

 

Well it's been a couple days and so far so good :-)

Happy to report that the 4WD is clikcing in properly and is engaging as it should.

Seems like all it really needed was to have the pins on the harness cleaned up a bit probably from the bit of off-roading that i do in mud, snow, and salt as it sees very little in the way of sand.

A good case in point to first look and troubleshoot the simple things before spending the time and effort in changing major parts only to find out that it's not the cause of your issues!

Thanks again to JMC for the knowledge and info for the in-dash switch.

I must say that i learned a bunch about the 4WD system by having this problem and NO money had to come out of pocket.

 

I have the same problems... My ABS doesn't work, light is on and the 4x4 doesn't engage. I don't understand what you mean by the pinpoints? What ended up working???

Thanks

 

Your problem is a bit diff than mine as i never got the light to come on.

The connector w/ the pins i'm talking about is the electrical connector for the electronic shift motor on the TC. If you crawl under the truck you can locate the TC and then see the wires coming out of the little motor that's attached by a few small bolts to the TC.

I unplugged the connector and sprayed electronics cleaner re-connected it and did that a few times and eventually it did the trick.

I'm in the snow/salt of Lake Tahoe a bunch during winter so i suppose the contamination got into the connector some how

Do some searching and you'll find lots of threads on the issue you have more specifically

 

Here is some food for thought. I have a Chevy Blazer besides my F150, and it has a 4x4 ABS problem.

Here is what the problem is with the Blazer. The speed sensor that is attaches to the hub is destroyed so my ABS light stays on. My 4x4 worked until that problem popped up. From my assumptions is that the 4x4 needs to know the speed of the wheels before it will engage the clutch to lock in the 4x4. In my situation, the vacuum kicks the hubs to engage but the differential doesn't do anything. Doesn't matter if it is LO or HI.

I am going to try and repair that hub in the next couple weeks so I can let you know if that helps me any. But I have a feeling you will solve your issue first.

 

Thanks for the insight and your reasoning is exactly why i made this thread as i was thinking the same!

However not sure if you read the entire thread but i found out what my issue was and it's now fixed after a very simple fix/clean

Although 4WD works 100% i still have my ABS light on just waiting to have someone w/ the proper ABS code reader to help me out lol!