2005 Suburban GMT800 NP246 No 4HI, goes to Auto 4WD

redhat

Original poster
Member
Mar 19, 2021
2
WNY
Good morning, I have a 2005 Suburban Z71 with 202k on the clock. I had to put a rebuilt transfer case in it. The rebuilt case has a Sonnax case save installed to prevent pump rub issues.

I picked up the truck (clean from Texas) weeks back and when I changed all fluids in the truck, the transfer case was about empty. I filled it back up with AutoTrak II, but the case was too far gone -- bearings felt horrible and the seals were leaking most of the fluid out.

Was pretty careful with the encoder motor, however, now when I shift it into 4HI, it blinks 4HI a few times then by default goes to Auto 4WD. I cannot get it into 4HI. It will shift into 4LO no problem, as well as go back into 2WD. I don't ever recall the t-case having to stay in Auto 4WD.

Is the encoder bad? Or possibly the switch? I have heard that I may have to have the Transfer Case control module re-programmed or reset for the new clutch packs in the new t-case. Has anyone heard of this? For reference this is the NP246 case. Is this a common dealer visit item or something I could do from a Tech 2?

Thanks!
 

gmcman

Member
Dec 12, 2011
4,656
Hard to say, could be your front 4WD disconnect not locking in. It does sound like a transfer case issue if you can get 4HI and not A4WD, but does the front encoder motor operate when selecting A4WD?
 

TJBaker57

Member
Aug 16, 2015
2,907
Colorado
Do you have an OBD2 adapter such as those used for apps like Torque Pro or OBD Fusion??

I have an 05 Yukon, 5.3 LM7 amd the 4 button 4WD system.
 

Mooseman

Moderator
Dec 4, 2011
25,487
Ottawa, ON
With the truck OFF, press each switch numerous times to try and clean the contacts inside.Then, with the truck in RUN but not running, put it in A4wd, you should hear a high pitched whine from the front, which is the disconnect actuating. Then going to 4hi, you should hear the transfer case shift. If it doesn't, could be the encoder motor or the transfer case is having a mechanical issue.
 

Brianmac.2ss

Member
May 14, 2024
1
Illinois
Good morning, I have a 2005 Suburban Z71 with 202k on the clock. I had to put a rebuilt transfer case in it. The rebuilt case has a Sonnax case save installed to prevent pump rub issues.

I picked up the truck (clean from Texas) weeks back and when I changed all fluids in the truck, the transfer case was about empty. I filled it back up with AutoTrak II, but the case was too far gone -- bearings felt horrible and the seals were leaking most of the fluid out.

Was pretty careful with the encoder motor, however, now when I shift it into 4HI, it blinks 4HI a few times then by default goes to Auto 4WD. I cannot get it into 4HI. It will shift into 4LO no problem, as well as go back into 2WD. I don't ever recall the t-case having to stay in Auto 4WD.

Is the encoder bad? Or possibly the switch? I have heard that I may have to have the Transfer Case control module re-programmed or reset for the new clutch packs in the new t-case. Has anyone heard of this? For reference this is the NP246 case. Is this a common dealer visit item or something I could do from a Tech 2?

Thanks!
Hey, did you find out what the issue was with this? I just put a reman NP246 in my 05 sierra 1500hd. I replaced the transfer case because of the pump rub issue. The old case worked fine but now the reman will not go into 4hi. It blinks and kicks it into auto 4wd. It goes into 4 low and 2 hi just fine. Seems to be the same problem you had with yours. Thanks
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,851
Tampa Bay Area
  • Like
Reactions: azswiss

redhat

Original poster
Member
Mar 19, 2021
2
WNY
Hey, did you find out what the issue was with this? I just put a reman NP246 in my 05 sierra 1500hd. I replaced the transfer case because of the pump rub issue. The old case worked fine but now the reman will not go into 4hi. It blinks and kicks it into auto 4wd. It goes into 4 low and 2 hi just fine. Seems to be the same problem you had with yours. Thanks
Yes I did, it was a simple fix that it seemed like no one encountered before, but never the less, easy.

I had to replace the transfer case range selector ring, bought here on Amazon -> LINK HERE

It is essentially the ring inside the encoder motor that tells the 4WD system what position the transfer case is in. Once I changed it, 4HI, 4LO and 2WD all select without a problem and the truck no longer automatically goes into Auto 4WD by itself.

I replaced mine Sept 2023. Originally, before I replaced this piece, I used TechLine Connect and GM SPS2 to apply the latest calibration to the ATC (automatic transfer case) module in the truck as I had been told by some pretty bright GM techs/minds that the only way an ATC module will re-learn it's positions (compensation learned over time for clutch wear in the case) is when the module is programmed. That seemed to work for a while but eventually issues cropped up again.

I'd try replacing the ring... it's easy. Look it up on YouTube, the encoder is filled with a light oil so don't spill it out. It is O-Ring sealed. Keep everything clocked/oriented the same way you take it apart. If the ring don't work, then maybe try the latest calibration with SPS2.
 
  • Like
Reactions: mrrsm

Forum Statistics

Threads
23,394
Posts
638,791
Members
18,604
Latest member
vulcantoolman

Members Online