2003 chev silverado stuck in 4 lo

Vis

Original poster
Member
Feb 8, 2018
2
Rostock
Hello, The original problem was the truck wouldn't go into 4wd and there were no lights on the switch. I tested the switch and it tested good with all the correct resistances. I then pulled the module and opened it up and found a lot of corrosion so I replaced it with a used one from a scrap yard which was compatible with my truck. As soon as I plugged it in and started the truck it threw it into 4 low and I cannot seem to get it out. I put the truck into neutral and press 2 hi but nothing happens. I took the encoder motor off to see if that was the problem. Is there certain tests I can do to see if it is working properly ? I took the truck to a dealer because I was told the module had to be progammed. They could not get it to accept a program. They said the module was throwing a C0321 code. What tests and procedures should I follow?Thanks
 
Last edited:

Sparky

Member
Dec 4, 2011
12,927
From what I have understood this code usually points to the encoder motor being shot. Similar has happened on the GMT360 platform.

Not so much the module needs programmed (because it already is), but the motor ain't working right.
 

Sparky

Member
Dec 4, 2011
12,927
I don't know how similar the motor is to the one on the GMT360 but here's some testing that was done on a Trailblazer. May have to adapt it for a full size but it may be similar. I've not dug into this very deeply as I've never had this level of failure on my Trailblazer (just had a bad switch and disconnect), and my Silverado has never had a failure yet aside from a leaking axle seal.

https://gmtnation.com/forums/threads/trailblazer-stuck-in-4lo.10471/
 

Dr.Fiero

Member
Dec 7, 2017
161
S. Alberta
Not sure if it's the same part(s) as on the slightly later GMT900, but... I've had it happen on my 2008 Sierra where I got jammed in 4 low (thankfully I was right near home!!!). Although it's not really a 'fix', you can take the motor assy off the back of the T-case, and manually rotate the selector back to 4 high, or 2 high (do it with no load on the system, so block the wheels, in neutral, etc).

At that point at least you're mobile again. I just make damn sure to not use low anymore!
 

Sparky

Member
Dec 4, 2011
12,927
The transfer case is different on the GMT800 vs the GMT900, but not sure the level of differences.
 

Dr.Fiero

Member
Dec 7, 2017
161
S. Alberta
The transfer case is different on the GMT800 vs the GMT900, but not sure the level of differences.

Same here on not knowing the exact difference(s) - but seeing as they are both electrically operated (vs mechanical lever), there should be enough similarity that the base premise would still work (a motor rotates, and gets transferred into a linear action inside).
 
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