auto 4x4 Auto 4WD works, Fulltime 4WD doesn't

Cascadia Machworksllc · November 6, 2017

My 2005 Silverado 1500 Z71 has an issue with the 4x4 mode. My Auto 4WD works perfectly but when I put the truck in to Fulltime 4WD High or Low, the front differential does not engage. I can hear the internals change when I change it from Fulltime Hi to Low, but the fron diff does not engage. Again, when I change the selector to Auto 4WD the front diff engages and the truck is great!!! Anyone know of a fix for this or if this is a factory recall or fuse/wire/switch??? Thanks, Tim.

Chubbs878 · November 6, 2017

Either a faulty encoder ring or the transfer case module needs to be reprogrammed would be my best guess, short of an internal/hard parts failure.

Cascadia Machworksllc · November 6, 2017

Thanks, not sure what those are but I will research it and see if I can do the repair or must have my mechanic do it with specific equipment.

SunShine01 · November 6, 2017

I had a simile issue with my buggy truck, 2002 Z71 Avalanche.

It was a sensor on the axle not working properly.

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T_ClarkEx39 · November 6, 2017

2017 1500 LTZ Z71 with the 6.2 (my brother in law's), has the "auto 4WD", can you drive around with it in that mode all the time? Highway speeds and such? He does this quite often is the reason i ask. Is it actually "auto 4WD or is it AWD (all wheel drive) which is what is displayed on his information screen.

Logroller · November 7, 2017

10 hours ago, T_ClarkEx39 said:

2017 1500 LTZ Z71 with the 6.2 (my brother in law's), has the "auto 4WD", can you drive around with it in that mode all the time? Highway speeds and such? He does this quite often is the reason i ask. Is it actually "auto 4WD or is it AWD (all wheel drive) which is what is displayed on his information screen.

Manual suggests against it if there is no need for the 4WD.

Chubbs878 · November 8, 2017

@Cascadia Machworksllc

I may be wrong in my suggestion.

when you select modes, the info is processed through the control module (a separate piece of electronics located in dash behind the selector switches) and the motor on the transfer case turns the shaft, simultaneously the actuator on the front axle housing engages the front differential.

I misread the info as the problem is with the TC motor where the encoder ring is located. If I were you, would start off by having a 2nd person activate the different mode switches as I remove the front axle actuator and inspect for operation going from 2WD to 4A, back to 2WD -to - 4HI, back to 2WD -to- 4LO. If that functions properly then go back to the mode selector and inspect internally for damaged or separated connections.

Now, do you know for sure that the front axle isn't engaging? or could it be the Transfer Case isn't actually changing to 4WD? that test above will reflect a faulty axle actuator, but if the TC isn't sending anything to the front output, i could see how you think the front axle is not engaging but really the driveshaft has no input.