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Discussion Starter #1
Hey Guys,
I know this has been covered in other threads in the past, so I'm sorry to post another thread on the subject, but I've tried everything suggested in other threads with no success. Here's the story:
I replaced my tranny last year (did it myself and did so with the battery disconnected). Before the swap my 4wd worked perfectly and never had any issues. Once I plugged everything back in my new transmission worked great but the SVC 4wd message lit up and has been on ever since.

To remedy the problem I've tried:
-resetting the computer (many many many times for many many many hours)
-adjusting the neutral safety switch
-inspecting the TCM circuit board under the seat (no corrosion or evidence of blown components)
-replacing the transfer case shift servo
-replacing the font axle shift servo

Also, I don't believe it is the button assembly in the dash (all lights light up when the truck is started, then they all go out when the "SVC 4wd" msg comes up).

I've also pulled each of the 4 sensors on the xfer case and they functionally check out on the workbench.

Does anyone have any ideas or suggestions? Has anyone ever seen this before?

Detail on the truck:
3.5 I5
4wd z71
170k miles

Thanks!
 

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Make sure all the connectors are plugged to the right one? I think 2 of them can be plugged into the wrong ones. Also check the harness that it didn't get damaged on accident.
 

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Makes sure the pins didn't push back in the connectors so the pins can't contact correctly. GM has cheaped out on their connectors and the locks for the pins wear out easily allowing them to slide back far enough to not contact the other connector.
 

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Discussion Starter #4
Thanks for the responses guys,
I've checked the cleanliness of all the plugs and verified they were plugged into the correct mates. Also when I was cleaning them I inspected the pins and found no grossly mismatched lengths...

Any other thoughts? Has anyone had success troubleshooting these with a computer (I know a code reader can't check the TCM but maybe a techII or something)? The only other thing I can think of is check continuity and module output voltages, but am having a hard time finding the wiring diagrams/schematics.

Also, it's bugging the crap out of me that it most likely has to do with the transmission replacement but can't think of what that would have affected (other than the stuff already mentioned). Wanted to bring it to a dealer to have them check if the TCM "went to sleep" but they wanted to charge me $100 just to look at it.
 

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with the service 4wd on the dash can you attempt the shift?

can you hear the module on the transfer case attempting the motion

I spent many years trying to figure out my 4x4 without a serv 4wd error so atleast your computer knows that it isn't working, which leads me to believe its more of mechanical thing, I remember correctly the dash unit is what prompts the service 4wd , along with the under the seat module the sensors on the case should prompt the serv 4wd note...


if you can try to read throught the 4x4 no worky thread lots of troubleshooting in there

ill try to think of more ways to help as you gather more information
 

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Discussion Starter #7
I've checked the dash switch and the pins look good. All lights light up when the truck is first started (then all go out with the SVC 4wd message).

When I reset the computer I can hear each shift servo attempt to make the shift then quit. They will do this once every time i reset the computer, then I'm assuming the computer tells them to not attempt another shift once the "SVC 4wd" comes on.

At one point I took the Xfer case shift servo out and used the old servo to manually attempt to make a shift (just to see if the mechanicals were stuck or something). If i recall correctly I got about a 1/4 turn out of it then it wouldn't go anymore. Does anyone know if this is normal? If not maybe there's something sticking in the xfer case?

Thanks again!
 

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Any new info currently have the exact same problem I change my transmission in my 04 i5. And has same symptoms been trying to figure it out for months now
 

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Do you have a water leak in the back when it rains? I worked on an issue with the board under the driver's seat getting moisture on it because of that leak. The leak was coming from the third brake light.

Anyway... may want to check that
 

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No i think i need to have it reprogrammed because I did a ls swap. I can hear the tccm click when i hit the button and when I took it apart it was clean inside.
 
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