4X4 Will shift into Low but not High 4x4

[Agis8]

Adjusting 4x4 control knob, can hear clunk when TC shifts into/out of Low, but when set to High 4x4, it does not engage. Dash light indicates 4x4 High, no light flashing going on. Any ideas? Also, earlier, had front wheels off ground, engine running, in Park, put into 4x4 High and I can turn the front drive shaft by hand, both wheels rotate the same direction. No TC locking in High mode? 4x4 Low definitely works as confirmed by driving and turning at steering wheel lock. TCCM problem likely? Thanks for any help offered.

 

[Flash]

Possibly 4wd disengages but you just can't hear it.

 

[Agis8]

Possibly 4wd disengages but you just can't hear it.

I wish. But test on gravel confirms non-operation.

 

[Flash]

I wish. But test on gravel confirms non-operation.

That's not a reliable test.

When auto is selected, all the way to the left on the range selector, it will be in 2wd until a difference in wheel speed front to back is detected (wheel spin).

Then up to 35% drive is shunted up to the front axle. It's automatic 4wd.

 

[Agis8]

I was talking about 4WD High, not Auto mode.

That's not a reliable test.

When auto is selected, all the way to the left on the range selector, it will be in 2wd until a difference in wheel speed front to back is detected (wheel spin).

Then up to 35% drive is shunted up to the front axle. It's automatic 4wd.

 

[Purch1977]

Have you checked for error codes?

 

[Agis8]

Yes. None.

Have you checked for error codes?

 

[Flash]

I was talking about 4WD High, not Auto mode.

That was clever of me. I just gave you proof of the opposite of what I was trying to say.

I was saying that in a "gravel test" that the front wheels should spin when you're telling me they don't proving that 4wd isn't engaging.

Ok, thing to do now is take the shift motor off to see if it's doing what it should and also try manually engaging/disengaging 4wd while you're down there.

There's articles on this forum about how to test and repair the shift motor.

If the shift motor is working maybe you'll have to check the clutches in the transfer case.

Sorry about my earlier confusion.

 

[Agis8]

That's a good idea, to put it into 4wd High manually, though I wonder if my TC is marked as to the positions. From what I've read, I would never get into 4WD Low if the TC internal clutch coil wasn't working. When I set it for 4WD Low I can hear the shift motor running and the slight grind-clunk as it goes into and out of that mode (and have road-proven its whiny operation). And also, when I set it to 4WD High, that dash light does come on (which is supposedly feedback from the shift motor & not just the switch). I have opened the position sensor on the shift motor to check for the broken bump stop, but this one seems updated as it has a black rubber stop (no screw head visible) and seems firmly in place. As for the position plate electrical wipers, those are sealed/enclosed in the plastic gear housing cover one takes off first, so I have no idea if those are in good shape (but being sealed you'd think so). I'm left to wondering about the TC control module and if it is failing in some way.
Thanks for your interest in my travails.