1997 Tahoe 5.7L 4X4 Issue

[wirlybird]

Bad weather today so started the Tahoe and let it warm up.
Hit the button on the dash for 4X4 hi range mode and it blinked a bit and then engaged.
Drove about 5 miles and parked at the store.
Came back out and started the truck. 4X4 light now flashing and will not engage. Tried repeated times from 2 to 4 high range and it just blinks.
If I try hi to low range I get a clunk at the rear end so it is doing something but the low range light also just blinks. Makes a similar sound going back to high range.
One thing I did notice is when shifting from 2WD to 4WD or 4WD to 2WD, standing still and in neutral, I hear what sounds like a relay clicking in the dash near the left window pillar.
I have not checked fuses yet.

I thought maybe frozen but it was working until the truck was shut off. Then a restart and the 4WD light just blinks.

Thanks for any initial thoughts. I'll check stuff as I am able.

 

[olof1233]

Might have something to do with the transfer case that’s what my mechanic friend said about my truck

 

[Schurkey]

Ideally, you'd switch between high and low ranges with the truck moving about 2 mph, in neutral.

If you have no luck with that, you may have a failed wire harness, a failed "encoder motor", or a failed transfer case. More diagnosis needed.

 

[wirlybird]

Ideally, you'd switch between high and low ranges with the truck moving about 2 mph, in neutral.

If you have no luck with that, you may have a failed wire harness, a failed "encoder motor", or a failed transfer case. More diagnosis needed.

So sitting idle and in neutral when I switch from 4 high to 4 low I get a light "clunk" which seems to come from the rear driveshaft/rear end. I get a similar one going from 4 low to 4 high.
Searching posts I find that this "clunk" is not unusual when going from high to low range.
During this time the light on the 4 high or 4 low button never stops flashing.
Going back to 2WD the light switches and goes solid.

I did not try moving slowly in neutral. Snowing so doesn't roll well!
The odd thing is that it went into 4WD ok but it was after I restarted 15 minutes later that the 4 high light was flashing and 4WD was not engaged. I never took it out of 4WD.

I am suspecting the actuator on the front differential at this time. It is original.
The 4X4 has been slow to engage in the past and doesn't get used much.
Also going to replace the switches in the dash for good measure.

 

[wirlybird]

Update:
Truck is fixed. Replaced the 4X4 switches just for good measure.
Replaced the actuator and problem is solved. Truck now goes into 4WD with no issues. Just a worn out actuator!