Please help me diagnose this issue. I've replaced just about everything I can think of and I'm tired of wasting time and money.

As is common, 4x4 will not engage. Problems started with a blown fuse in 4WD slot. Replaced fuse, so far hasn't blown again, though I can tell there's a significant draw on the truck's electrical system when pressing 4hi. A 10a (which is lower than the fuses rating) blows straight away. Is there a common place for grounding issues to cause this fuse to blow? What are some other areas that I should look at for problems? Here's the story thus far:

97 4x4 Blazer:

- Replaced encodor motor
- Tried two different actuators
- Replaced Transfer Case Switch AND vacuum line to actuator.
- Replaced Front Diff Shift Cable
- Replaced selector switch in dash

When I pull a battery terminal and let it rest for a bit, plugging the terminal back in causes 4x4 to work perfectly for maybe a trip around the block. If I am in 4hi, the 2hi light will flicker randomly. Clicking in to 4Low will engage the gear, but no lights are on. Eventually, it "locks" and the 4low light illuminates, transmission will shift to second. Sometimes, pushing 4lo will illuminate both 4hi and 4low buttons.

Yesterday, I installed a "new" TCCM. 4x4 worked awesome. Quick response from encodor motor, locked in positively, put probably 10 miles on switching back and forth BUT the 2hi light would still flicker randomly. Seemed flashy when I'd hit a bump or, oddly, when I was in park. Parked the truck with working 4x4 last night. Came out this morning, fired up, and began all of the symptoms previously described. Of course we have six inches of snow on the ground this morning, and I had to get to work, so I haven't had a chance to mess with it.

Also, on old TCCM, I pulled codes 1 and 2: internal TCCM fail, and Encoder Motor Circuit Fail. After parking last night on "new" TCCM, the TCCM hadn't logged any fresh codes.

Lastly, it's hard to tell if it's due to running the heater at full blast all morning, but the case on the TCCM seemed to be a bit hot.

I've replaced pretty much everything that needs to be replaced on these, so I'm at the end of my rope. I've dug for hours, and haven't had luck finding anyone that has run into the same symptoms, so hoping someone reads this that has dealt with this before. Thanks for any thoughts.

 

Sounds like maybe the encoder motor isn't able to freely move the transfer case internals? You've already replaced all the other stuff. With the encoder motor removed can you click the transfer case through its range, using a wrench?

 

Hi Les. I replaced the encoder motor last fall, and I had no trouble clicking through all three positions while the encoder motor was off. Also, when I disconnect and reconnect the battery, allowing the TCCM to ostensibly reset, I find that I am able to shift into 4hi/4lo very easily; works great. After some time passes, the problem resumes. I do hear the encoder motor try when 4 hi is selected, but it will not fully engage. Also, pressing the 4x4 switch does nothing -no click, no flashing, no anything - unless I am in neutral.

 

Maybe you have a ground or wiring problem - only thing that is really left - the rest of the system is new. You can check grounds by using a DVM between the transfer case and battery ground or between TCCM ground and battery ground. Shouldn't be reading more than about 0.3V at any time. Also I believe I read there is a big wiring ground on the underside of the passenger compartment that can get corroded and should be checked.

Only thing I would think might be different after disconnecting the battery is the encoder might go through a preset sequence to do a self-test. Maybe having done the full range or a certain part of it (or starting from a slightly different place), it will work for a bit. I know that HVAC door actuators do that on my Avalanche, Not sure about encoder motor though. This is all PURE speculation.

 

How much do you trust the "new" TCCM?

 

I located and repaired the issue! Managed to get into a warm dry shop and remove drive shaft and d/c encoder motor harness. Long story short, the wiring harness conduit had fallen and was resting on the front driveshaft. The rotation of the drive shaft ate through the insulation on the wires.

I cut the damaged portion and respliced using waterproof butt connectors, then several wraps of electrical tape. Zip will keep it out of the way going forward.

 

Congrats on finding the issue and nice sleuthing!

This is a good cautionary tale for everyone to add this to their list of things to inspect when doing to any maintenance or repairs.

Also thanks for posting your solution. These final reports are really useful to people.

As for your repair with a final layer of electrical tape, I've become a big fan of the self-fusing silicone tape often found under the brand-name "Rescue Tape." I've used it on many applications including repairing the ABS wire that had its insulation worn through by my front wheel rim. It really does fuse to itself and makes a tight seal to surfaces around with it is wrapped. I had occasion to confirm that it really does fuse to itself when I had to remove some of it once. It is great for protecting electrical connections exposed to the environment and especially for those exposed to wet environments.

My preferred way to repair electrical connections is to solder, use heat-shrink tubing then cover with the self-fusing silicone tape. If I cannot solder, I'll use crimp connectors that have heat shrink insulation as a substitute for the solder+heat-shrink.

 

Nice! Glad you figured it out, and I'm glad you posted the conclusion to it! Might help somebody in the future

 

I've used the silicone tape on my boat. Good call. Wish I'd had some on hand for this repair.

 

It is always good to see someone figure out the problem and report back after they fixed it