1997 Explorer XLT - 4WD Not Engaging

[wcsd106]

Hello All.

Now that I have my 1997 explorer XLT starting reliably, it is time to move on to the second item on my priorities list... Getting the four wheel drive to engage.

Here's what I have so far.

With the front tires jacked up off the ground, I was able to turn both wheel and observed the front driveshaft turning.
Prior to starting the vehicle, the 4x4 and 4LO lights illuminate during the lamp test.
Turning the control trac switch from 4Auto to 4HIGH or 4LOW prior to starting the engine or while the engine is running has no effect, whether the vehicle is in park or neutral.
Regardless of switch position, no clicks or indicator lights are observed
All fuses in the drivers side panel and the power distribution box test good with a multimeter. I did a visual inspection of all fuses related to 4wd for good measure.

This early in the game, I would expect an electrical issue over a mechanical one, but I'd like a good nudge in the right direction as far as troubleshooting.

I've been doing some reading and will continue to do so while I await responses. Thanks again for all your help.

 

[wcsd106]

Not a lot of time to work on the Explorer today, but I did pull the bezel and remove the 4wd switch. The indicator light in the switch is dead, which is not surprising, but the switch appears to function correctly... varying the amount of resistance shown depending on switch position. I disassembled the switch to check the internals, and the resistance I'm seeing at the terminals corresponds to the markings on the surface mount resistors on the board. (Electronics is my forte)

With the switch connected to the harness and the key in the run position, I observed three distinct voltages between the center pins on the switch depending on switch position. 1.2v, 2.x, and 3.x volts.

I am attempting to locate the brown wire to determine whether I have voltage on that wire in any position of the switch.

Open to any suggestions, and I'll continue reading.

 

[drdoom]

Probe the brown wire at the transfer case, truck running switch in 4x4 HIGH, you should have about 5.9VDC. In 4x4 AUTO you should have about 0.6VDC.

 

[wcsd106]

I've seen it mentioned that I can get at the brown wire from inside the vehicle by removing a seat. Is that true?

 

[XLTrunner]

Can access the brown wire from behind the radio (remove the GEM module) or under the driver seat.

 

[wcsd106]

Pulled the drivers seat today. Almost had it pulled yesterday except for that pesky T50 Torx seatbelt bolt. Didn't have a torx bit that size, so used that as an excuse to buy a new set of Torx sockets.

Accessed this connector under the carpet below the drivers seat. I'm assuming the brown wire I'm looking for is on the top row furthest to the right? The color is a little washed out due to the sun getting in the way, but that's the only solid brown wire in this bundle.

With engine running and the 4wd switch in either 4HIGH or 4LOW, I have 0 volts when measured from that brown wire to ground. Going to probe that wire from the GEM module to the connector with engine off to check continuity and will be hoping for a broken wire, but I seriously doubt that will be my issue.

Should I be looking at a GEM or Relay issue at this point?

 

[wcsd106]

*Update 10.12.2016*

This morning, I probed from the brown wire shown in the picture above, to the brown wire coming out of the Transfer Case Shift Relay. I have continuity through that wire, so my hopes of it being a broken wire are shot.

While I was in there, I removed the Transfer Case Shift Relay and brought it to my workbench. I disassembled the relay housing and tested the relay using a multimeter and a 12v power supply. The relay coils are good, and the relay contacts switch the way they should. The U1515 TO-220 mount diode also tests as good, and the two resistors are showing the correct resistance, so at this point, I would beg to argue that the Transfer Case Shift Relay is good.

So, here is where I stand at this point:

• The two 4x4 indicator lights on the instrument panel light up when the vehicle is started then go away.
  
• The 4wd switch on the dash tests good with the exception that the bulb is blown in the indicator light
• The Transfer Case Shift Relay was bench tested as good
• The Brown wire running from Transfer Case Shift Relay to the connector under the driver's seat has continuity
• 4WD does NOT engage when the 4wd switch on the dash is turned. The Transfer Case Shift Relay does not click
• There is no indication that the Transfer case motor switches into LOW Range when 4LOW is selected
• No Voltage is observed on the brown wire in any switch position

I'm looking for suggestions as to how to proceed with troubleshooting at this point.


On a side note, the Transfer Case Shift Relay uses 4 simple components (2 resistors, 1 relay, 1 TO-220 U1515 Diode), all of which are easily serviced. I'm not sure what a new Transfer Case Shift Relay is running these days, but the electronic components used in this assembly can be had for less than $10. If anyone is interested, I can provide a schematic and a parts list for the Transfer Case Shift Relay. This would allow users to simply replace defective components in their assembly. That is, if it would be cost-efficient to do so.

 

[wcsd106]

*Update 10.13.2016*

Using a copy of the 4wd wiring diagram I located in the forums, I've verified that my two 12v supplies to the Transfer Case Shift Relay are giving the relay the correct voltage.

I have also checked across the transfer case shift motor terminals with an ohmmeter and verified the motor windings are at least intact.

I have checked the transfer case electronic clutch wiring with an ohmmeter and verified that those windings are intact.

I am not getting any signal to engage the transfer case shift relay regardless of switch position.

** Question ** The more reading I have done, has led me to believe that some problems I throught were unrelated to the 4wd system and hadn't began troubleshooting yet could be relevant. The cruise control does not function or turn on even though the switches are electrically OK. Also, the clock or compass or whatever it is in the top center of the roof above the windshield does not light up. Reading has led me to believe those are all tied in with the GEM module.

At this point, I believe the GEM module is at fault and will be replacing it unless someone else wants to jump in and assist me.

 

[Turdle]

Before assuming the GEM is at fault, try this overhead console fix. It is pretty simple, and very common for it to not work due to cold solder.

Read the tips first.

http://www.explorerforum.com/forums/index.php?threads/overhead-console-display-fix.187953/

 

[wcsd106]

* Update 10.15.16: PROBLEM SOLVED *

This afternoon I received the GEM module in the mail that I purchased on Thursday. I installed the GEM as soon as it arrived and then tested the 4wd functions. I now have 4AUTO, 4HIGH, and if I switch to Neutral, it will go into 4LOW as it should. Took it for a quick trip around the neighborhood (Didn't want to go further since the drivers seat is still sitting in the cargo area) and everything functioned as it should.

Thank You to everyone who took the time to assist me with this.

Also, before I button everything up, I'll remove the transfer case shift relay, disassemble it, and do a writeup on how easy it would be to rebuild one of these... That way someone can save some money down the road.