Are there any ALDeer members that are mechanics? Specifically, familiar with late 90's/early 00's F150's....

I have a 1998 F150 4x4 with the electronic dash knob 4x4.

My 4wd quit working a while back. It just got to the point where you'd turn the knob from 2hi to 4hi and nothing would happen. It simply would not engage. I did a lot of research and found a common problem where the electric motor on the back of the transfer case that turns the output shaft from the 2hi to 4hi/4lo positions would often go bad and had to be replaced.

No problem, I replaced it. 20 minute job. problem is it's still not working. turn the knob from 2hi to 4hi.......nothing.

I've found 2 fuses, 1 under the dash and 1 under the hood, that are associated with the transfer case shifting process and both are fine.

at this point, I don't even know what else to check.

Could also be a vacuum line. If I remember right from my '03 F350, they have vacuum lines that actuate the hub when you turn the knob on the dash. One little crack in that line and it won't work anymore.

any idea how one goes about checking them?

I should also note that the dash lights for 4wd do NOT come on when I turn the knob. from what I've read, these are triggered by the output shaft on the transfer case moving to a given position, so even if the hubs were not engaging b/c of a broken vacuum line, the transfer case would still be shifting which would trigger a dash light. since this is NOT happening, I'm thinking the transfer case motor is never turning the shaft to begin with.

So if that's the case, the problem is somewhere between the dash knob and the transfer case shift motor.

Is the knob/switch bad, not giving a signal for things to switch?

Switch we went through it with my uncle's truck. It an 01. About a week later it quit working again. That time was a vacuum leak. He just replaced the line.

checking the switch and the plug going to it are the next step.

The more I'm reading, I'm finding that IF it were a vacuum issue, the dash light would still come on and the transfer case would still be shifted, the hubs just would not be engaged b/c they are what is vacuum-operated.

But when I turn the dash knob, nothing happens. just HAS to be electrical.

That truck has a transfer case electronic module under the dash that is probably bad.I had a 4x4 salvage yard for several years and stayed sold out of those modules and transfer case motors.Common problem. The vacuum lines only engage the ft. diff, they don't have anything to do with engaging the transfer case.

I had the same problem with my '07 and found out about a vacuum switch that could be bad. My light would come on but while troubleshooting it I seem to remember that when I took the electrical connector loose on the switch, the light didn't come on then. I may be wrong, but I replaced the switch and it fixed my problem of not having 4wd. Mine would work sometimes and not at other times (it never worked when I needed it). The switch is located behind the battery on the firewall and cost about $26 at a local parts store.

Read this one. It tells how to check all of it.

mash

I had a 95 Ranger that had the same problem. I checked both the shift motor and switch and they both tested to work. Finally friend mentioned the relay. It was under the dash and I had to remove the stereo to get access to it but it worked fine after replacing.

Located behind and above the stereo on that F-150 also.About the size of a cigarette pack with a connector on 1 side.

Awesome. Is that something i can test with a multimeter? Also, any idea what itd cost to replace?

Gomer,

Did you ever pinpoint your trouble?

I haven't had a chance to look at it anymore this week. I haven't had 4wd for nearly 2 yrs so I'm not in a huge rush. hopefully can look at it some more this weekend

OK, good luck. It sounds like you know how to use a meter, so you can get to the root of it all.

I hope whoever designed the electrical/4wd system in these trucks dies a slow, horrible lonely death.

well, maybe not, but almost.

I've narrowed it down to the transfer case shift relay module. The problem, now, is that it's located under the dash and behind the radio. I've done TONS of research online and the only way I can figure to get to them is completely disassembling the entire dash. I've tried to get to them about 4 different ways, to no avail.

I've never been this angry working on a vehicle. I'm to the point I may never buy another Ford vehicle just because of the problems I'm having thanks to the POS design of this system.

I had the same problem happen to me on my 01. Same issue with yours (no light and no engagement). I was sure it was a vacuum line or the motor on the transfer case. I took it to a friend who read the codes and said for some reason there were several odd codes that had showed up. He cleared them and its worked great ever since. Sounds ridiculously simple and may be covering up a problem but worth a try.

does the selector switch on your ac/heater work. I mean changing the air flow from your feet to de-frost to vent. If it works then its not your vac. line.

yes, that works fine. it's not a vacuum issue

You think your pissed now. Wait till you replace the part get it back together and it hasn't fixed the problem.