This is a plea, I need to do some driving tonight.
Last night I engaged 4wd low, all is good. Got in it a while ago, tried to turn it off and it is stuck. Not just the indicator, it is in low 4wd. Hit 35 or so didn't release. Backed up 10-15mph no release. Pulled switch out, unplugged, indicator still lit up. Haven't tried to drive with switch out, yet.
I haven't messed with anything recently, put glow plugs in 3 months ago.


Thanks in advance.
Tom.

 

I have had customers vehicles towed in like this. What I found 90% of the time that gets them back to normal is

Drive the vehicle at 1 mph for about 30 feet....
1. Bring the vehicle to a complete stop.
2. Depress the brake.
3. Place the gearshift in N (Neutral) (automatic transmission) or depress the clutch (manual transmission).
4. Move the 4WD control to the 4x4 HIGH position.

*It can take up to 45 seconds for the shift command to be sent to the unit*

 

If you absolutely cannot get the truck out of 4 low you can pull the shift motor off of the transfer case and manually shift case with a pliers or wrench.

If you flip the switch and nothing happens your low to hi relay could be bad, you could try flip flopping the two relays around.

Those are both 2 options to try, the first will get you out of low if you absolutely need to be though. If possible you should pull codes, see if you get any, it will give us a better place to start.

Baatzy

 

Mr White, you are a savior. Must be the name! It worked. A couple of seconds after I switched to hi the low light was off, switch off and good to go.
Thanks to both, glad the first worked.

 

Made my 42 miles home just fine. Have to ask, since this is the first time this happened, what's up? Funny part, low range hasn't been working for over a year. I haven't needed it, so have been lazy about tracking down, but might be a good time?

 

Here are some things to consider and possible way forward with troubleshooting the ESOF System:

Transfer Case 4x4 — Electronic Shift on the Fly (ESOF)
The 4WD control module accomplishes shifts by interpreting inputs from:

a. MSS
b. Vehicle speed signal (transmitted from the ABS system)
c. Gear motor encoder plate position
d. Brake pedal switch
e. Digital TR sensor (automatic transmission)
f. Clutch pedal position (CPP) switch (manual transmission)
g. Ignition switch

Based on these inputs, the 4WD control module controls the shifts into 2WD, 4X4, or 4X4 LOW with the following outputs:

a. Low to high relay (clockwise)
b. High to low relay (counterclockwise)
c. Pulse vacuum hub lock (PVH) solenoid
d. Gear motor encoder assembly

The electronic shift-on-the-fly (ESOF) system has a feature which allows the driver to override the vacuum operated hub locks. When the front hub locks are manually turned to the LOCK position, the hub locks are locked at all times, overriding the vacuum operated system. If the front hub locks are manually turned to the AUTO position, the hub locks can only be locked by turning the MSS to 4X4 or 4X4 LOW position.

DIAGNOSTICS

Tools: Bi-Directional Scan Tool / Vacuum Pump and/or Gauge)

RETRIEVE THE DIAGNOSTIC TROUBLE CODES (DTCS)

CHECK FUSE #27

CHECK FOR VOLTAGE TO THE PULSE VACUUM HUBLOCK (PVH) SOLENOID - Measure the voltage between PVH solenoid C1247, circuit 295 (LB/PK), harness side and ground.

CHECK CIRCUITS 605 (RD) AND 145 (GY/BK) FOR A SHORT TO VOLTAGE - Measure the voltage between PVH solenoid C1247, circuit 605 (RD), harness side and ground; and between PVH solenoid C124, circuit 145 (GY/BK), harness side and ground.

CHECK CIRCUITS 605 (RD) AND 145 (GY/BK) FOR A SHORT TO GROUND - Measure the resistance between PVH solenoid C1247, circuit 605 (RD), harness side and ground; and between PVH solenoid C1247, circuit 145 (GY/BK), harness side and ground.

CHECK CIRCUITS 605 (RD) AND 145 (GY/BK) FOR AN OPEN - Measure the resistance between 4WD control module C281b pin 6, circuit 605 (RD), harness side and PVH solenoid C1247, circuit 605 (RD), harness side.

CHECK THE PVH SOLENOID COILS - Measure the resistance between the PVH solenoid terminal 1 and terminal 3; and measure the resistance between PVH solenoid terminal 2 and terminal 3.

CHECK ENGAGE VACUUM SUPPLY TO THE RIGHT KNUCKLE - Make sure hub locks are in the AUTO position. Lift and support the vehicle off the ground until the front tires can be spun freely.

NOTE: The engine is required to be at idle during the following steps to supply the vacuum required for the hub locks to engage and disengage. Start the engine and allow to idle.

Turn the MSS to the 2WD position and wait 15 seconds. If switching from 4X4 mode, wait an additional 45 seconds. Disconnect the vacuum line at the right front knuckle and install a vacuum gauge on the line.
Disconnect the vacuum line at the left front knuckle and plug the line.
Turn the MSS to 4X4.

NOTE: Normal operation applies engagement vacuum for 45 seconds and then drops to 0 in-Hg.

Observe the vacuum reading within 45 seconds._ Spec: Vacuum reading greater than 10 in-Hg.

Turn the MSS to 2WD.

NOTE: Normal operation applies regulated disengagement vacuum for 15 seconds and then drops to 0in-Hg. Observe the vacuum reading for 15 seconds. Spec: 5.8 and 7.3 in-Hg.

Remove the vacuum gauge and connect the vacuum line at the right front knuckle and perform same tests.

Tom

 

Well, that should keep me busy.


Thanks Tom.


Tom.

 

A general tip for 4WD...

If you have a spot where you can back up a very slight grade, back up about 10 feet and put it in Neutral, hit your selector switch, and gently drift to a stop.

Else, you can back up and stop, hit your selector switch to whichever position you want, and after about 1/2 sec, let off the brake for a moment to let it drift forward a hair.

This can take the strain off the drivetrain, helping it go into or out of 4WD.

You can do the same forwards, but backwards seems to have the best results.

Oh- Wheels must be STRAIGHT for best engage/disengage results, no binding allowed