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Discussion Starter #1
I plowed the last 2 days and toggled bewteen 2wd and 4wd with no issues. This morning I tried to switch to 4wd drive and realized it wasn't engaging. The "service 4 wheel drive" message popped up and the knob to change from 2wd - 4wd light was stuck on 4wheel drive (i turn it to 2wd drive and it showed that it was in 4wd) but 4wd wasn't working. I turned the truck off for about a minute and the knob was working but I was still unable to get the 4wd to work. No error codes.
It's a 2008 silverado 4 door ltz 5.3.
Any ideas ?
 

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Call and ask the dealership how much but ensure they r ONLY scanning the single problem. U may b able to pay a dealer mechanic some bones at lunch. Just ask to speak to the electrical mech in person. I don’t use the scan tools enough to buy. I would check the solenoid on the side if it was me. Both my 12’ & 94’ 4wd’s have an internal solenoid? The 94 takes about 8 seconds to lock after shifting into 4H. The solenoid may have frozen temporarily? Not sure but RayVoy is brilliant on all things Auto. Give him a shout. Sorry for ur plight. J
 

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Thanks for the kind words John, let's see if we can get him going.

The '08 has a new design t-case, made by Magna Powertrain.
Not many reports of problems with these boxes.
MP bought the old NP/NV operation from GM and Chrysler, I suspect the same engineers designed the new box, so a lot of the electric circuits are probably similar to the old circuits.

The guys are right, the correct way to locate the problem is to read the trouble one(s).

But without the codes, there are 4 places to consider.

These are old design problems; but may apply to the new cases

The connections under the truck, water will screw it up, check for water and clean

The shift motor has a finger assembly on the end of it, to sense where the motor has rotated. The fingers, electrical conductors, can get knocked out of place.

The switch, has small resistors, changing the switch position changes the resistance and the voltage to the control module.
The voltage value is the position signal from the switch.
The switch contacts can get dirty.

And the last is the front axle actuator. When any 4x4 selection is made, the operated actuator locks the passenger side outer and inner axle halves together.
When this is fully operated, a contact closes to signal the control module that the front driveshaft clutch can be engaged.
 

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Discussion Starter #8

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Discussion Starter #9
Dealer said the Axel is broken and needs to be replaced. Hopefully that's the cause. If not, then they'll keep diagnosing. More to come
 

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Sorry I'm late to the party. AutoZone around Colorado has Bosh brand scan tools for sale and borrow. They read all the modules I've ever run across, including ABS. I bought a small one that rides in the truck for $200 if I remember right.

Hope they get you taken care of. My experience with dealers is entirely dependent on their culture. in Greeley, the GMC dealer and the Chevy dealer are owned by separate people and are separate lots a few blocks apart. One is always a pleasure to deal with and I avoid the other like the plague. Which we incidentally have in our prairie dog population...
 

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Hate to say this; but I can see that being a problem.
The newer 1500 trucks are not strong enough to use as a plow truck.
Fine when the wheels are on snow/ice, lots of slip; but clear the snow, back up and drive on bare pavement in 4WD and something will break
 

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Discussion Starter #12
It ended up being the driver side axel ($300 to repair from my mechanic and the $150 diagnostic fee from GM). I've been plowing with that truck for7 years now. I take it easy when plowing. We got hit with almost 2 feet of snow, that's what did me in. Thank you all for your input and suggestions.
 
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