2008 Silverado 2WD converted to 4 WD

This guy brought me his truck and just as the title says he converted his 2008 2WD Silverado to 4WD...The engine is the stock 5.3, he used the stock 2WD 4l60E transmission and the transfer case is from a 2003 Silverado 1500...Everything works perfectly & there are no DTC's at all in 2WD & 4HI....But as soon as he shifts the transfer into 4 LOW it won't shift at all until you let off the gas pedal, but by then you've bounced of the rev limiter about 15-20 times...He took the truck to a couple of shops and they all told him that he needed to have a 4X4 OS flashed into his TCM T-42...I just happen to have a spare T-42 TCM from a 2008 4X4 Silverado I did some work on, so I installed the TCM Licensed it and NO GO! I worked on it for 3 hours, changed just about every parameter in the Tune and nothing, it won't shift from 1-2 in 4LOW...
I'm thinking there's some sort of sensor missing, that the transmission needs when it's in 4LOW but I don't know what I'm looking for...:shock:

The transmission has the 20 way connector plugged in to the passenger side. The transfer case has 2 female connectors/plugs on it, one is for speedo and I don't know what other one is for...
Anyone got any ideas? I'll try anything...

Hello GameOver,

You always seem to have an interesting project on the go !

With Gen III platforms the 4WD low range function was initiated by a switch that grounded a PCM pin (usually C2 pin 16) - this signalled the PCM to alter the shift pattern being used.

With the Gen IV platform, I believe the same principle applies - grounding ECM connector C1 (or J1 / X1 however you refer to that connector) pin 2 should alter the shift pattern to 4WD low.

Given that the 4WD low shift pattern is initiated by the ECM, this is why swapping out the TCM had no effect.

I don’t know if you will also require a signal from the front axle switch (C1 pin 3) - or if that is simply used to illuminate the “4WD” lamp in the IPC.


Regards,
Taz

Taz,
So because the truck originally was 2WD(harness is difeerent from 4X4) I would have to physically wire in to pin #2(J1/X1) on the ECM, and when It's shifted into 4Low, that pin would have to be grounded, to allow transmission shifting to occur in 4Low...Makes sense though...:D
I would have thought the TCM would need the wiring done!
Gonna try it Monday morning...

On Gen III trucks, GM tended toward a “standardized” type wiring approach. As an example, trucks that didn’t come factory equipped with cruise control, generally still had the cruise control wiring harness segment from the base of the steering column to where the cruise (or TAC) module would be located under the hood - which made retrofitting cruise control very easy.

I haven’t started doing Gen IV conversions yet, so I’m not sure if the ECM wiring harness in GM trucks are “universal” between 2WD and 4WD drive applications - it would make sense to only use one harness - that had the potential to “plug into” all factory options.

Good luck on Monday … let me know if your 2WD harness has pins / wires at the C1 (J1 / X1) pin 2 and pin 3 locations - if it does, it would mean that harness is compatible with both 2WD and 4WD models.


Regards,
Taz

Well,the stock harness didn't have wires in Connector J1 pins 2 and 3...So I wired 2 pins, sent a ground signal to ECM and it still wouldn't shift normally! Still need to let off throttle for transmission to shift...:frown:
I tried grounding them separately & together but made no difference.

Sorry to hear that didn’t work out. Thank you for the update on the 2WD versus 4WD wiring harness.

Noticed the other thread you found regarding the woes of 2WD / 4WD component swapping / interchange and subsequent tune issues. Sounds like other people have run into this same issue with Gen IV ECM / TCM / BCM communication (and interdependence) when attempting to get 4WD low to function appropriately in a retrofit type application.

Problems like these remind me of all of the reasons why I enjoy working with Gen IIIs !!


Regards,
Taz

Yeah, I read that whole thread and they both got it to work...(4X4 4Low) by grounding pin #2 and having the right OS.
I haven't given up though, it has to be something I'm overlooking or something very simple(especially with a manual transfer)...:D

I couldn't get a valid 4 lo signal without a BCM in a 2007 5.3/4l60 swap, wouldn't shift in low range. I tried several OS's and C1 #2. Ended up placing the VSS on the TOS and flashing in a 2wd tune. Works perfect; however VSS reads incorrectly in 4lo at the ECM. Used the transfer case VSS for the dash so it always reads correct.

Good morning,

I have a 2008 silverado 5.3 2wd, I want to convert to 4wd. any links to a forum where someone did this? I know I need cv arms, front diff, front and rear drive shaft, transfer case(i am ok with manual since the electric style would be more complicated) what other hardware do I need? I don't plan on using 4lo out of first gear so this isn't a huge issue for me, as long as 4hi works ok, for towing the camper thru the desert/dunes. This is just so far the best link i have come to as far as being exactly what I need.

Thanks for all the help!