new user, great forum.
Have a 97 Explorer 4x4. lately when I start the truck it has shifted itself into 4x4 low. I had disconnected the battery for a few minutes, re-connected and the truck was back in auto.
This no longer works and it is stuck in 4x4 low. Mechanic wants to replace transfer case encoder, but says more diag needed after to replacing encoder motor to determine internal failure and may need more work.
Can I simply have the 4x4 low disengaged manually?
Can anyone help?

 

Do you know what kind of troubleshooting the mechanic did? If he didn't do any, I'd say he needs to do more diagnostics before he replaces the motor, not after. The motor (or the position plates) is a common failure as the motor rarely gets used and corrosion can build up and dirty the contacts.

It seems like something is telling the GCM that 4WD low is selected. The 4WD selector switch and the transfer case relay deserve a look.

The below information is based on the assumption that your '97 is like my '98. I looked up the transfer case motor, the transfer case relay and 4WD mode selector switch on Rock Auto. The '97 and '98 use the same relay and could use the same motor, depending on whether you have the BW1354 or BW4405 transfer case (16 pin connector). The switch is a different part number, but it could be functionally the same. I don't know this for a fact, though. Again, this is based on the assumption of similarity.

You'll need an electrical schematic to troubleshoot. It will be impossible or very difficult and slow to do troubleshooting without the proper documentation. The 4WD selector switch provides a resistance to the GCM depending on the mode selected. If the switch has failed such that it only provides the resistance for 4WD Low, then the GCM will command 4WD Low, provided other conditions are met (DTR sensor in park/neutral, speed is 0, etc.).

The relay contacts could be stuck/shorted such that power is provided to the shift motor to shift into 4WD low. Or, you could have a short to ground downstream of the relay in the H2L (high to low) circuit. I guess there could be an internal fault in the GCM that provides the ground as well.

I suppose there could be a failure in the transfer case motor that is providing the wrong position to the GCM, but I don't know what that failure would look like in terms of what pins should be open/closed for the various 4WD modes. The EVTM is lacking in terms of what's going on inside the GCM and the motor position plates.

I would do the following:

1. Check resistance across the two pins that provide the resistance to the GCM with the switch in 2H, 4H and 4L. Since your switch is different from mine, I'm not sure the pins would be the same. Resistance should vary in each position.
2. Check continuity across pins 10 and 3 of the transfer case relay. There should be no continuity when in 2H or 4H.
3. Check continuity from the wire that connects to pin 9 of the transfer case relay to ground. If there is continuity, remove the connector (C282 for my '98) at the GCM and see if the ground is still present. If not, the ground is being provided by the GCM so there could be an internal fault in the GCM or it thinks it needs to provide the ground based on the 4WD mode switch.
4. Remove the connectors for the transfer case motor, relay and mode switch and check for bent pins, corrosion, etc.

If you want to disable 4L but still have 4H, it looks to me like you'd have to remove the #9 pin/socket from the connector at the transfer case relay. If you remove the whole connector from the relay, I think you'll lose 4H. It's hard to tell because the EVTM doesn't show what's going on inside the GCM or torque-on-demand relay.

Both the switch and the relay are spendy items so I don't think you want to throw parts at it. But, if your mechanic bills out at $100/hr and wants 5 hours to troubleshoot, it might be cheaper to replace the parts. The transfer case motor, relay and 4WD mode switch are each about $80 at Rock Auto.

 

Mikeman....you are the Man!!
Thanks so much for the in depth detail. My mechanic was impressed and we now have direction. I'll let you know the outcome.
Thanks again

 

Don't thank me yet. That's just me thinking out loud with a schematic in front of me. There's probably some troubleshooting steps in the drivetrain section of the shop manual that provide a lot more info. And of course, there's that big assumption, but it should provide ideas even if very little is applicable to your year.

I can't emphasize enough how important it is to have the proper documentation. Otherwise, it's a shot in the dark.