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Discussion Starter · #1 ·
I bought a 2002 trailblazer ls this summer, and I dont know what's wrong with 4we. The selector switch has no lights on at all. I tried turning it back and forth, cleaned the pins, and sprayed contact cleaner on the wire harness. Nothing. Makes no noise, dosnt switch into anything, just stays in 2wd. I'm in chicago, would really like to figure this out. Please help.
 

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Have you tried pulling the fuses for the 4WD system, waiting a minute or so then replace them? There are 2 of them. Sometimes when the TCCM (transfer case control module) detects an error it disables the whole system. Pulling the fuses won't fix the error but might bring the system back online so you can see what's happening.
 

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Discussion Starter · #3 ·
Yes I pulled the one under the hood and under the seat. Let it sit about 20 min before replacing. Theres no response. Not even a service 4x4 light. Nothing! At least if it made a noise or lit up, I would know where to start. But I'm lost.
 

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The lights get their power from the Body Control Module (BCM). This is so they can be dimmed. I have run into a user whose system worked fine but the lights did not and we traced that to a dirty flat ribbon connector at the BCM. But you say yours makes no noises either so that different. If you turn the 4WD switch with engine off, key on, drivers door open so you can hear you should certainly hear something if either of the 2 different shifting motors were working.

Assuming all this is true then my next step would be to have a look at the connections to the TCCM. Have you done that yet? You can see these connectors by popping off the small access panel at the left end of the dashboard, by the drivers door hinge. There are 3 harness connectors to the TCCM in there. 3 in a row, I think 2 blue and one black. Let me find a picture of that....

IMG_20190915_152825_HDR.jpg

IMG_20190915_152857_HDR.jpg


First off make sure it is actually in there! And then see that all 3 connectors are there. There's no telling what previous owners may have done.

If you have a meter and know what to do with it then check for power to the unit. I know the connector on the left, the black connector with 4 wires, should have power in the orange wire, and ground on the black wire that is NOT next to the red wire. That orange wire comes from the 25 amp fuse under the hood. I have to check wiring diagrams to refresh my memory on others...... Ok, there is one other ground wire that is on the far right connector, top row, left end. A black wire with white stripe. There is a second black/white wire on that same connector but that is not a ground or power and it isn't on the top row. Here is a diagram....

Screenshot_20210103-093014~01.png
 

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No doubt somewhere someone will mention that the 2002 models had troubles with their TCCM modules. There indeed was a technical service bulleting (TSB) about the early TCCM not "waking up" from sleep mode when they should. Most all of the various modules are powered all the time even without a key in the ignition and they go to a sleep mode when the truck is off and wake up when an event like opening a door happens. That particular issue with the TCCM not waking up required the fuses to be pulled and reset. You've already tried that and still got nowhere but I thought it was worth mentioning.
 
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