HELP - no power at the rear wheels 2015 Sierra 1500

[bTanZ]

Help trouble shooting ... please!?!?

 

- While driving my approx. 100,000 mile, 2015 GMC Sierra 1500 up a paved hill, in 2-wheel drive, in the rain, with no additional payload ... I felt a mild "slip" followed moments later by a loss of power transmitted to the rear wheels ... note: there was no noticeable noise, grinding, etc. at anytime prior
- I rolled down the hill backward with the truck in neutral
- While on a flat paved surface I tried multiple positions on the gear selector, etc. and still no power at the rear wheels 
- I engaged the 4-wheel drive, power was transmitted to the front axle and wheels and I dragged it home on the front axle approx. 6-miles at 40mph and parked it

Curious to learn if theres anything electronic on the vehicle (6-speed trans., or t-case) that may have failed (since there was no mechanical noise and little warning other then the mild slip prior to failure???
I plan to try and establish where the failure is (guessing t-case or rear axle) by mechanical inspection in the coming hours/day .... any suggestions for methods ie. trans and t-case in neutral spin rear drive shaft manually and see if theres any resistance in the rear end?  Any other trouble shooting suggestions??

I tried the search and found nothing ... perhaps this is already documented somewhere you all may direct me to?

THANK YOU

[swathdiver]

Well, is the rear drive shaft still attached?

[bTanZ]

23 minutes ago, swathdiver said:

Well, is the rear drive shaft still attached?

yes i should have mentioned that ... the entire drive line is intact, no fluid escaped, etc..

[asilverblazer]

My guess - something in the t-case or rear diff busted. Driveshaft probably still good, otherwise it would have been making an awful racket on that 6 mile drive home.

[asilverblazer]

Put it in park in 2wd on a hill when it starts rolling have someone look and see if the driveshaft is turning with the wheels (something in t-case) or not (something in rear axle).

[bTanZ]

20 minutes ago, asilverblazer said:

Put it in park in 2wd on a hill when it starts rolling have someone look and see if the driveshaft is turning with the wheels (something in t-case) or not (something in rear axle).

 

good thinking!! 

[Mawz]

23 minutes ago, asilverblazer said:

Put it in park in 2wd on a hill when it starts rolling have someone look and see if the driveshaft is turning with the wheels (something in t-case) or not (something in rear axle).

Alternatively, put it in drive on the flats and and have some one spot to see what spins. If the driveshaft spins it's the diff and if it doesn't it's the T-case. 

[CrawlSlow]

Jack stands

[bTanZ]

1 hour ago, Mawz said:

Alternatively, put it in drive on the flats and and have some one spot to see what spins. If the driveshaft spins it's the diff and if it doesn't it's the T-case. 

 

yup ...even easier!

[bTanZ]

Alright so i just jumped in it in the driveway in 2-wheel drive and it drove down the driveway fine, window open and no funny noises etc. ... I went back and forth in the driveway fw/reverse and all seemed normal.
 

I took it for a lap around "the block"(i live in the woods) ... and everything operated just fine...

When it failed (and I posted this post) it it was in the rain ... is there anything in the t-case or otherwise that can disengage the rear drive shaft electronically???

[bTanZ]

On 9/11/2021 at 3:35 PM, bTanZ said:

Alright so i just jumped in it in the driveway in 2-wheel drive and it drove down the driveway fine, window open and no funny noises etc. ... I went back and forth in the driveway fw/reverse and all seemed normal.
 

I took it for a lap around "the block"(i live in the woods) ... and everything operated just fine...

When it failed (and I posted this post) it it was in the rain ... is there anything in the t-case or otherwise that can disengage the rear drive shaft electronically???

 

so i did a follow on test drive and i think i have an intermittent trans. problem and the use of 4wd to get home from initial failure on the hill may have been coincidental with the intermittent problem.   this most recent test the truck is whining when it back/down shifts and my wife said she could hear it whining as I drove by her.

 

BTW trans fluid is at proper level, no funny odor and was swapped out approx 15,000miles ago

 

I'm going to try and get it to someone wit a better diagnostic tool (Snap-on, etc.) then I have to look closer at trans.

[asilverblazer]

Sure sounds like something electronic acting up, I think engaging transfer case or changing gear lever position, shutting off and back on, etc. is resetting whatever electronic is misbehaving.

[rlcole321]

I would definitely like to hear the end of this scenario!!

[bTanZ]

the earliest available GM dealer Transmission Diagnostics available appointment is Sept 24th ... i'm on the side lines until then

[swathdiver]

1 hour ago, bTanZ said:

the earliest available GM dealer Transmission Diagnostics available appointment is Sept 24th ... i'm on the side lines until then

You can buy your own GM software online, the MDI with GDS software, hook it up to a laptop and diagnose and test it yourself.  You would use this tool in conjunction with the shop manual, which you can subscribe to at AllDataDIY for a nominal fee.  It will pay for itself just for this issue.