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2003 chevy trailblazer_ltz
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Discussion Starter · #1 ·
I had some 4x4 problems with my 2003 trailblazer. My wife drove it for a month around town on dry pavement in 4hi.

At first I thought it could be the front acutator, but I took it apart and it was fine. I cleaned out the old grease and put new stuff in.

Then I thought it might be the transfer case shift motor, so I bought a new one and installed it. This did not fix the 4x4.

When I took the encoder motor off again I noticed that the shift shaft coming out of the transfer case turned easily. and figured that the shift arm had broken.

I bought a low milage transfer case from ebay to replace the broken one. Checking out the new one is shifts properly though all the modes using a pliers on the shaft. When turning towards the AWD and 4HI direction from 2hi the clutch pack had good tension.

I replaced the case, the old one was definately broken. The shift shaft turns very easily and it clunks inside, their is no reistance and it doesn't shift between modes.

I thought great I found the problem and I will now have 4x4 again. With the new case 2Hi works, and 4lo works (the actuator engages and all 4 wheels spin), but when I select A4WD or 4HI the indicator light just flashes and goes back to 2hi. I can hear the encoder/motor trying a couple of time to shift before it gives up and goes back to 2hi.

Does my TCCM need to be recalibrated for the new transfer case? Since the clutch pack is tight and like new in this case? Is the TCCM trying to turn the encoder motor to far to engage the clutch pack for A4WD and 4HI. With the old broken case I would guess that TCCM was turning the shaft very far clockwise to engage the clutch pack to match the front and rear wheel speeds.

Randy
 

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2004 gmc
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He said he regreased the front actuator - I assume that's what we call the splined disconnect. That takes grease.

Your other issue is very interesting. The TCCM probably tried its best to keep up with the positioning of the clutch plates that were disintegrating out from under it. The factory manual talks about the algorithms being designed for adaptive positioning of the encoder motor in A4WD mode, since as the clutch packs wear, the pre-positioning needed to get 5% of the torque bias towards the front changes. But 4HI mode should be in a fixed position set for maximum torque transfer, and I don't believe that position has any adaptive learning.

I'd certainly try to borrow a TCCM from a local person for an experiment. You may have low torque coming out of the encoder motor, but that's rare if you read all the failure reports here.

Do you hear the expected noise out of the front actuator ONLY in the 2HI->A4WD mode transition?

I assume you pulled the TCCM fuse to force a reset? That might do a recalibration and not require a dealer visit.
 

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2003 chevy trailblazer_ltz
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Discussion Starter · #4 ·
I have tried removing the #8 fuse (TCCM) but I'm not sure how long it would take to erase its memory.

When I reistall the fuse and turn the ignition key forward the 2HI indicator lights up solid. When I switch to 4AWD or 4HI I hear the encoder/motor straining a couple of times while the indicator light is flashing over the appropriate mode, then the motor stops trying and the indicator light returns to 2HI.

If I put the transmission in neutral and select 4LO the encoder motor moves and then I hear the front disconnect acuator engage. When I select 2HI I hear the encoder/motor strain a bit and then hear a slight pop from the transfer case, followed be the front disconnect disengaging.

I think that I don't hear the front disconnect actuator when I select A4WD or 4HI because the TCCM first waits for the transfer case to be in the correct position before commanding the front disconnect actuator to engage.

It almost seems like the encoder/motor is weak. The other encoder/motor I bought doesn't work either, but I may have damaged it. When I first changed the encoder/motor on the bad transfer case I had to rotate the new motor's position to install it on the transfer case. I did this by unbolting the electric motor from the planetary gear reduction and moving the planetary gears until the shaft was lined up with the transfer case and bolted the electric motor back on. when I installed it on the transfer case and tried to switch between modes the motor just buzzed a few times and stopped trying. What I realized is that the brake was not disengaging. this was because when reinstalling the electric motor on the encoder assembly you must ensure the 4 wire connector is fully connected to the electric motor connections by pushing on the harness from the bottom of the encoder with a small screwdriver. I fixed this connector but their is a slight burnt smell in the electric motor. It wont shift the Tcase into 4HI or A4WD either.

It still seems like the TCCM is trying to turn the transfer case shift arm too far clockwise. When I turn the shaft manually I can switch the case easily, but there is quite a bit of tension when turning clockwise to the A4WD/4HI modes, I assume this is the clutch. With the old broken case the TCCM must have learnt that to engage A4WD it would have to turn the shift arm extremely to try and stop the rear wheels from turning faster than the front wheels. If the 4HI position is not an adapted position then it should still work. But if 4HI is not adapted eventually as the clutch plates wear its position could be less clockwise (if that makes sense) than the adapted A4WD setting that compensates for clutch wear. I'm guessing that 4HI is also adapted and may be simply adapted as a few more degrees clockwise than whatever it has determined as the best position for A4WD. Any thoughts?

Can the TCCM be cleared by simply disconnecting the battery? or does it require dealer intervention?

Randy
 

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2004 gmc
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Excellent analysis. I haven't seen a theory of operation of the TCCM that goes to that level of detail of the algorithms. Most modules other than the PCM don't have flash memory, so 30-60 seconds of no power should be enough to reset anything that be reset outside the dealer. Sorry I can't help more, as you have a totally unique problem.
 

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Discussion Starter · #6 · (Edited)
I found this information on the web that refers to GM 4x4 vehicles, it looks like a TCCM relearn is required after I changed the Tcase:

You must perform the clutch
relearn process after any of these situations:
• The transfer case was replaced.
• The TCCM was replaced or reprogrammed.
• The transfer case was rebuilt or
internal repairs were performed.
Clutch reset with a scan tool:
• Key on, engine off.
• Access the Special Functions menu
with your scan tool.
• Select Clutch Reset Procedure
(Motor Learn Procedure).
When the Clutch Reset Procedure
is initiated, you should hear the motor
engage, indicating a successful learn
procedure.
Clutch reset without a scan tool:
• Key set to accessory.
• Switch into the 2 High mode.
• Turn the switch clockwise past
4 Low into the neutral request
mode and hold it for 30 seconds.
You should hear a noise from the
motor, indicating a successful learn
procedure.

This artical wasn't specific to the trailblazer, and I tried to do the clutch reset procedure without the scan tool, but it doesn't seem to do anything (I may not be doing it right)

Has anyone heard of a procedure like this for the GMT360 platform?


Randy
 

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Discussion Starter · #8 ·
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I replaced the TCCM in my 2003 trailblazer with one from a 2003 envoy, now everthing works 100%. I suspect a tranfer case re-learn would have worked as well, but changing it was easier than taking it to the dealer (cost me $125)
 
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