AWD to 4WD Conversion Complete

After putting 100,000 miles on my '06 Denali, going through 3 front differentials and two transfer cases, I decided it was time to make the conversion. Everything is complete and running great! Total cost...approx $2000 (and that includes a reman transfer case). These procedures are for installing the 4-button electronic selectable transfer case system (Auto AWD, 2H, 4H, 4L).
I will post the part numbers of the various items later....but in a nut-shell, here's what was necessary:
Parts to order from GM:
1-Wiring harness for the shift actuator (new)
1-Wiring harness from the engine compartment to the transfer case (NP246) (option code NP8) (new)
1-T/C shift motor, backing plate and 3 bolts to bolt it on (new)
Other parts needed:
1-Dash wiring harness and engine compartment wiring harness from donor truck (salvage yard)
1-NP246 Transfer case (with 3 speed sensors…you’ll have to buy the sensors if your unit doesn’t come with them) (great deal on a remanufactured unit from TransfercaseExpress.com)
Pay attention to your Option (RPO) Codes….If you have a M32 option code (4L65E) on your Denali, then you need to order a T/C for a M30 trans (M30 Trans (4L60E) at it has 27 input splines vice the 32 on the MT1 (4L80E)).
1-Rear drive shaft from a 2003-2006 quad cab 4x4 (salvage yard) (1” shorter than the Denali shaft)
1-Front driveshaft from a 2003-2006 pick-up with NP246 T/C (salvage yard) (1” longer than the Denali shaft)
1-Front differential from a 2000-2006 4x4 (you’ll use only the actuator side of the differential and all of the axle shaft and coupler parts) (salvage yard)
1-Front Inner axle bearing (the AWD differential does not have this bearing installed) (new-autoparts store)
1-4-button switch in the dash (salvage yard)
1-T/C control module (buy a Dorman branded unit as it does not require programming like the GM units do when it’s first installed) (new-Amazon)
1-T/C control module mounting bracket (this is the plastic bracket that holds the T/C control module in place under the dash) (salvage yard)


Removed a complete wiring harness from a donor '06 Sierra and picked out the 4x4 portion (GM does not make a 4x4 only section of wiring harness for the interior of the truck). This required de-pinning and re-pinning a bunch of connectors. The interior harness included 98% of the wiring needed and the engine compartment harness included two wires from a connector under the Main fuse panel in the engine compartment down to the PCM. (Also, Do Not just cut the sections you think you’ll need as some wires will run about 2-8 inches in one direction and then makes a u-turn inside the harness.)
Take a bunch of pictures of the wires you need to remove and where they are in the connectors. This will pay huge dividends on the re-install!!! I also re-taped the wires as how they should lay-out in the truck. This helped when installing the new wiring and keeping things clean and neat.
The fun part of wiring is getting the wires through the rubber donut at the firewall. Use of a screwdriver to enlarge the rubber hole where the current wiring goes through while pushing/pulling the harness through is advisable.
I spent one day alone installing the wiring harness into my Denali that I had picked apart from the donor. I only had to splice in a couple of wires into existing wires as a couple of the pins in various connectors had only one wire vice the two I needed. This is a bunch of “under dash” work, so plan on being on your back. Most of the connectors that wires are added to are the main connectors that are attached to the rear of the fuse panels, removing those connectors from the back of the panels makes it a bit easier.
Day 2
Replaced the u-joints in the two driveshafts
Replaced the transfer case (bolted right in) Make sure you use the GM fluid for the NP246 (Auto-Trak II)…it’s different than the NP149 AWD fluid.
Installed the driveshafts
Removed the right side of the front differential (front differential assy removal from the truck is not necessary but you might want to remove the nuts that hold the aluminum support bracket on the right side to give you some flex room.
Install the Inner axle bearing. This goes inside the differential carrier on the pass side and is what the “short-shaft” rides on. It is NOT there in the AWD versions.
Install the right side axle assembly according to the repair manual. Don’t forget to check (and adjust) axle end-play IAW the manual.
Install the front actuator wiring harness and the T/C wiring harness. The speed sensor wire currently in the truck (that used to plug into the T/C) will plug right into the new harness. Pay attention to the wire color codes in the plugs and which sensor they plug in to. One is for the front shaft speed, second is for the rear shaft speed, and the last is the VSS.
Reprogramming of the PCM is not necessary. The Denali PCM software includes the 4x4 coding.
Here are the part numbers I used for the install/conversion (GM unless noted):

Transfer Case Harness - 15895628
Front Axle Actuator Harness - 15771689
T/C Actuator Insulator - 12384973
T/C Actuator/Select Motor - 19125640
Bolt (3) - 25624810
T/C Control Module - Dorman # 599-114
4WD Select Switch - 19259313
Transfer Case - NP246 for trans RPO code M30
Frt and Rear Driveshafts from a '03-'06 Sierra Ext Cab 4x4 (143.5" wheelbase)
Frt Differential - '00-'06 Sierra/Silverado/Yukon/Suburban
Wiring Harness (Dash and Engine Compt) - '06 Sierra (that is what I used)
Frt Inner Axle Bearing – Timken B2010

Total cost for me was $1931.00. Still cheaper than buying a new truck!

Hope this helps anyone that is interested in removing the AWD and replacing it with a selectable 4x4.

Wow this seems so backwards to me, but great writeup. Glad to hear it is working out for you. If you were close I might think about buying the awd stuff from you.