I am working on my 1999 F-350 Super Duty diseal and the <NOBR id=itxt_nobr_1_0 style="FONT-WEIGHT: normal; FONT-SIZE: 100%; COLOR: darkgreen">4x4</NOBR> light isn't coming on. I've tried the A/C test too see if it was the hoses coming from it but everything passed with flying colors. The two hubs in the front aren't engaging either in on the fly or while siting still. What could this be? I'm ready to ram my head through a wall here . Is it the resistors? how do I test them? fuses maybe? Any help would be greatly appriceated! <!-- / message --><!-- BEGIN TEMPLATE: ad_showthread_firstpost_sig --><!-- END TEMPLATE: ad_showthread_firstpost_sig -->

 

If you get no 4x4 light, your transfer case shift motor is probably bad or corroded up. You may be able to get it working by lightly banging on the shift motor from underneath the truck. If this method works, then you need a new one. the Corrsion will return.

 

I don't have the ESOF I have manual 4x4 but it is my understanding that the switch on the dash does two seperate things, 1. sends a vac. pulse to lock/unlock the hubs and 2. engages the transfer case. Can you hear the transfer case click? If so, maybe the light in the dash is burnt out, that happened to me on my 4x4 and cruise light this year, just a thought, but probably not that easy.

 

alright were going to go give these a try i'll keep you guys posted on what happens thanks so far

 

cworley is right. When you flip that switch it activates your vacuum pump to send a vacuum pulse to your hubs but if there's a break in the line you're gonna have to flip the hubs manually. In regards to the light in the dash, it's powered on the back side of the xfer case motor so the motor has to engage the 4wd in the case before it turns that little idiot light on. You should be able to turn your key to the on position without starting the engine, flip that switch and hear the xfer case motor engage. If you hear nothing then it's not working. They are notorious for going bad. The whole ESOF set up is sh**.

 

Okay so I'm back...I got onto the crawler and slid under the truck and gave the shift motor a good tapping nothing happened so I took my test light too it. It seems like it's not getting any power too it, does anyone know what fuses go to it? Or what could be causing it not to get power?

 

Knowing how ESOF is supposed to work ought to help you troubleshoot it. Note that I refer here a lot to the 4WD control module. On 2003 and older trucks, replace 4WD control module with GEM module.

When you turn the switch on the dash to 4WD, the first thing that happens is the 4WD control module activates one of two relays under the hood. That relay powers the shift motor at the transfer case to shift it into 4WD. Along with the shift motor at the transfer case is a set of switches that provides feedback to the 4WD control module, indicating whether the transfer case is in 2WD, 4HI or 4LOW. That entire unit is called the gear motor encoder assembly.

When the 4WD control module gets the signal back from the gear motor encoder assembly, it knows the transfer case is in 4HI and turns on the 4x4 dash light. Then it sends a signal the the Pulse Vacuum Hublock (PVH) solenoid, causing the solenoid to apply vacuum to the hub locks, causing them to lock.

When you turn the switch back to 2HI, the reverse happens. The 4WD control module activates the OTHER of the two relays, causing the shift motor to turn the other way shifting the transfer case out of 4WD. The encoder indicates this back to the 4WD module, which turns off the 4x4 light and eventually sends a different signal to the PVH solenoid causing it to send a smaller vacuum pulse to the hubs, causing them to unlock.

Now, in your case you're not getting a 4x4 indicator light. The first thing to check is if the light is actually working or is burnt out. Both the 4x4 and Low Range lights should light momentarily when the key is first turned to run and the dash console goes through it's self tests. If the 4x4 light doesn't come on here, then the bulb is burned out. You need to fix this before you can do much more troubleshooting. If the 4x4 light is working, but not coming on when you try to shift to 4WD, you know the transfer case is not shifting.

There are a few things that can cause this. One, the 2WD to 4WD relay is bad or has a bad connection, the shift motor is bad, or has a bad connection, or the 4WD control module is bad.

Most of the time, the problem is the relay. Occasionally the problem seems to be the shift motor and rarely it seems the problem is the module. I base this on my own experience and from what I have read here over the last few years.

The relays are in a relay box under the hood, on the drivers side firewall up close to the back. It is the only relay box with just two identical relays in it and nothing else. A common diagnostic procedure is to swap the two relay's position. Since one relay turns the motor one way, and the other turns the motor the other way, and it's likely that only one of them has gone bad, swapping the positions should cause the truck to go into 4WD and not come back out. If this happens, then replace the bad relay and you're good to go.

If this doesn't help, then you are left with the slim possibility that both relays are bad, or the shift motor is bad. A good way to test this is to unplug the shift motor wiring harness from the shift motor at the transfer case. It's the plug on the transfer case with just two wires. Put a test light between the two pins of the connector and have someone turn the switch to 4HI with the key on. The test light should light momentarily, as the control module tries to turn the shift motor to 4HI. If the test light lights, then most likely your shift motor is bad and needs replaced. If the light doesn't light, then you're back to the possibility of one of both relays being bad, or the 4WD control module being bad.

Another thing that happens occasionally is the windshield leaks water down onto the control module, causing corrosion in the wiring plugs of the module itself. The control module is behind the glove box. Open the glove box and push in on the sides. This will allow it to open further and allow access behind it. Inspect the control module and connectors and wiring for evidence of corrosion.

Note that I didn't speak much about the hubs and vacuum leaks and stuff. This is because the 4WD control module won't even try to lock the hubs until it sees that the transfer case has shifted. Until you get the transfer case shifting properly, worrying about the hubs is a waste of time.

 

I would quote you to say thanks but i don't thin we need the page 10 miles long but I will try all of these methods listed. I'll get back to you guys in a couple mins once I've tried them out.

 

That was great info D thanks, even though I don't have ESOF I work on a few trucks in my fleet at work that do, so I will file this in the "may need it later" file.

 

Hey D that helped a ton we went all the way through the entire system and replaced all the resistors and everything. Even though it wouldn't work at that point! so we all got frustrated and decided to pack it in. Put it in reverse and it worked....well we all shat a brick and had one of those "no ****ing ****" moments. But with out that post we would be up a creek. Thanks too everyone :]