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Discussion Starter · #1 ·
I have a 2003 Sonoma pickup and the 4wd is not engaging. The truck has 168k on it and this is the first issue with the 4wd. Have not started looking into it yet, is there a common failure mode for these? I am hoping for something not so expensive of course!
 

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B4U Task Force Admin
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Moved to Transmission/Rearend.

Lots of recent threads on 4x4 failures lately....might do a search.
 

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Been there Done it
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That's the most common cause. Dry rotted 19 year old vacuum hoses. Replace them one at a time to prevent mixing them up. Like @ProCycle says it's often one of the short ones between the master cyl. and the ABS. The short one into the reservoir could have popped off. It's tricky seeing the nipple in the fender almost behind the ABS.
If you have 15+ inches of vacuum at the actuator, it's the actuator. If you have vacuum to the transfer case switch, but not past it, it could be stuck. No fixing it, Just get a new GM 89059420 one. DO NOT USE A DORMAN SWITCH UNDER ANY CIRCUMSTANCES. It'll leak and fail in under 6 months if you do glue it on or duct tape it to stop the leaking.
But I'd check all the hoses first.
 
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Discussion Starter · #5 ·
Thanks for the tips, I will start with the vacuum lines. I see people talking about a transfer case motor, is that something else that can go wrong?
 

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Discussion Starter · #6 ·
So, there is vacuum at the actuator and it will move the actuator but not with the cable attached, with a little assistance, it will move the cable and 4wd will engage. Pulling the cable by hand feels difficult, not that I have any basis for saying that, but a new cable will be here in the morning. Do cables go bad? I had not used the 4wd since last year, is it like a parking brake cable that if you don't cycle it now and then it will bind up?
 

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Discussion Starter · #7 ·
It now works, if I had taken deerlayers advice and checked for the amount of vacuum it would have been a quicker job. There was vacuum at the actuator, but not enough to pull the cable, figured the cable was binding, replaced that and still no dice. Inspected the vacuum lines and the one from the engine to a T before the reservoir was rotted, replaced that and all is good. Obviously that would have been a better place to start but now I have a new cable and a good understanding of how it all works.
 
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