I have a 1998 F150 4x4 with the 5.4 engine and electronic 4X4 activation.

I have read all the posts I could find relating to activating the four-wheel drive. It's late and about 10 degrees F outside, so I haven't checked the actuator or other parts for proper operation. I will in the morning.

However, my truck is acting so strange I thought someone may have an idea that will help.

I got up at 5:00 a.m. this morning to go hunting. It snowed about four inches last night so I put the switch in the 4H position. Nothing happened.

I had to cancel my hunting trip.

Later that day, after things warmed up a little, I went on an errand for my wife. On the way back while stopped for a light, I flipped the switch around from 4H to 2H, and even into 4L. Nothing happened. I put it back in the 4H position and continued driving.

So about a mile down the road, doing about 25 mph, I'm in the 4H position but the truck decided to shift to 4L. Jumped like a bugger, but the road was slick enough that I slid instead of losing my transfer case.

Now it wouldn't shift out of 4L so I drove the rest of the way home at about 10 mph.

Here's the strange part-after letting it sit for a few minutes, I went out and it shifted right out of 4L and into 4H, but the light on the dash didn't come on. Then I noticed that when I step on the brake, the light does come on. Also, If I don't have my seat belt connected, when I step on the brake the beeper goes off--it doesn't work any other time. The 4X4 is erratic as hell. Sometimes it's in 2H, sometimes 4H, and sometimes it jumps to 4L, all while the switch is in the 4H position, and it all seems to be tied to the brake.

Any ideas?

 

welcome

1st off check the vacuum lines to the front axle actuator...making sure of no leaks.

2nd might need to remove the actuator and make sure the plunger rod is free moving ..sometimes from lack of use they get sticky.

3rd does this sit outside a lot? you mentioned it snowed
if yes you may have a windshield leak and moisture is getting into the control module shorting things out, resulting in all kinds of wonky issues. Thinking that is the GEM?

4th did you happen to notice if the "tow light" on the end of the shift lever is flashing as well during this erratic behavior...if so then you have a transmission code tripped and only a more in depth scanner will read it. Not the standard scanner they offer at parts stores.

lastly maybe, (hopefully), your switch is just funky and needs replacement .

 

An added comment to this is when it is in 4L that tells you the transfer case motor has rotated to it's second position to increase gear ratio.
Only then will the shift sked change and go into low range up and down shifting.
I would drop the transfer case motor for inspection and cleaning.
You will see a circuit board with wiper contacts that tells the PCM to make the shift program change for 4L and some other functions.
The other possibility is a leaking windshield dropping water onto the GEM module under the dash.

Good luck.

 

I did some tests and found that nothing happens when you turn the switch to 4H or 4L most of the time. No vacuum, no actuator, no nothing.

Sometimes, however, (Once today) I step on the brake and the seat belt beeper goes off. For the next few minutes, every time I stop the beeper goes off. If I turn the 4x4 selector at these times, it works and the truck is in 4-wheel drive. However, the 4X4 indicator on the dash only lights up when I step on the brake.

Pretty soon, the brakes stop making the beeper go off and the 4x4 selector doesn't work anymore.

My windshield doesn't leak, but I bought the truck used from the county. It was a road-crew truck. The windshield could have leaked at some time in the past. I am having trouble with the interior lights as well. They quit working during wet weather last spring. It does seem like any problems the truck has are related to the weather (strange).

 

No, the tow light doesn't come on.

Thanks again for the help!

 

Are you stopped when trying to engage into 4L?? Its best that you are. & it works better that after switching from 4L to 2wd to be stopped as well and back up for a few feet.

What beeper....maybe mine is broken IDK?? I never heard a audible beep or chime when switching from the 4H to 4L or back to 2wd in any combination there of. Was this an option??

might be wise to double check the grounds in the cab and chassis....the county like to add a bunch of extra radios and stuff

 

The range if issues suggest you need to replace the GEM module.
The interior lights are timed from the GEM plus 4wd and other functions.
Otherwise one function has no direct relation to the other.

If the GEM has corrosion from past wet conditions anything can happen that makes little sense until you realize the connection it has to all the functions it performs.
Also look around for attempts to fix the problems by others who had no idea how things worked. They may have botched things up good.
When they could not fix it it was put up for sale.
It's likely how you come to be here asking.
Good luck.

 

Yes, I understand and follow the shifting into 4L procedures. In fact, I'm stopped when I shift into 4H or back to 2H as well.

The beeper isn't a four-wheel drive beeper. It's the beeper that goes off when you don't fasten your seat belt. When it is doing this, the seat belt icon on the dash goes on as well.

Does the brake pedal have a sensor or something that could be sending the wrong messages to the GEM? If so, where is it and how do I test it?

Anyone have an idea how much the GEM costs, and what dealers charge to program it?

Thanks

 

My owners guide says to go in neutral for 4x4 low.

 

The GEM has inputs & outputs to & from the brake system, the neutral safety switch, the interior lights, power windows, 4wd and other sources.
If they get crossed on the GEM circuit board from conductive corrosion, anything can happen anytime, out of control.
Your not the first to see the results of this happening.
Good luck.

 

I pulled the GEM. It doesn't have any sign of water damage. However, it is covered with dust. The truck was a county road-building crew truck, so it's seen its share of dusty roads.

I cleaned the board and contacts off with some electronic cleaner. I'm going to put it back in and see what happens.

I think I will also look it over with a magnifying glass. Tiny cracks can cause circuit boards to misbehave, too.