NV4500 LQ9 Swapped 1999 Silverado 2500

Yeah, I bought another truck...

The short story is, I'm beginning the process of building a house and the 128i wasn't really going to cut it for what I needed. I couldn't justify buying a fourth vehicle so the 128i had to go. I ended up selling it for a bit more than I paid for it in 2020 and started shopping for GMT400s and GMT800s. I had pretty much given up finding what I wanted when this truck popped up. A 1999 Silverado 2500 with very little info in the ad. I went and looked at it and it needed some work, which I shouldn't be getting myself into on a daily, but I was pretty much sold based on it being a truly rust free truck in New England and, of course, the 5 speed. I almost talked myself out of it based on the work it needed. The owner hadn't got the push button NP263 working with the swap, the power steering and consequently the hydroboost wasn't working, and the mildly built 6.0 needed tuning. Then he named a price that would be worth it for a rust free shell around here and I just couldn't leave it. So here it is.

It's a little bro-trucked but, as much as I've made fun of them, I'm kind of liking it. I might even lean into it. I've swapped a GMT900 center console in, replaced the power steering pump, added aftermarket heated seat kits, and started trying to figure out HP Tuners. I've at least got it to no longer idle at 12 AFR. The engine supposedly is an LQ9 with Gen 4 pistons and rods, a BTR Torque Cam, 36lb injectors, TBSS intake, 90mm throttle body, and a trunnion kit. I can only confirm whats visible. 

I wasn't really planning on doing a build thread for my daily but trying to find info for making the 2005 NP263 work in a 1999 NP246 truck made me realize I was kind of on my own. So, if anyone else is dumb enough to try this instead of just swapping in a manual transfer case, the next post will explain what I did to hopefully make that work.

So, this truck was originally a 4 button NP246 truck. The previous owner swapped the NV4500 in with a 3 button NP263 behind it. In theory that could be solved with just a TCCM and the transfer case wiring harness, but... This being a '99 means it has the older style TCCM with a different connector. The two TCCMs are below. The black case is for an 05 NP263 and the metal case is from the 99 NP246. 

So I bought a 05 TCCM with the pigtails and got started. I was originally planning on splicing all the wires as needed but I realized that, though the connectors are different, they are the same style and I could just depin the 99 connector and repin the wires into the 05 connectors. So this is the TCCM connector in the truck.

And pulling the pins, which took some figuring out

Before I got too carried away, I pulled the pins in the 05 connectors

And prepared my wiring diagram

Then just moved each pin, one at a time, from the 99 to the 05 connectors

And all the pins moved over. Takes a lot more wires to run an NP246 than a NP263

Then the 4 pin connector is the same on both TCCMs but I still needed shuffle some pins

Same deal, depin, repin

And now I have an 05 NP263 TCCM plugged into my 99 Silverado

That's great but I still need to get the transfer case wiring harness from an 05 NP263 truck installed

The encoder motors have different plugs between the NP246 and NP263 so this is necessary regardless. Unfortunately this isn't quite a plug-in affair either. My wiring diagram for the engine bay connectors is below. You can ignore the diagram for the switch/selector. I ended up just buying a 99-02 3 button selector and it eventually worked with no wiring changes.

So one side of the harness plugs into the transfer case, the other side plugs in a the engine bay fuse box. The engine bay connectors are what we need to work on. Luckily the 4 pin C150 connector for the front axle plugs right in, as well as 3 pin C153 connector. The first one we need to change is the big 12 pin C151 connector.

Yup, they're both female connectors. Not sure if the difference is because of model year or transfer case type. I just spliced the 99 connector into the 05 harness.

And then, the C154 connector is a 6 pin on the truck and a 3 pin on the 05 harness. Again not sure if this a is a model year or transfer case difference.

I just built some new 2 pin connectors, as the 05 NP263 harness only has 2 pins in the C154 connector.

And now it should work, right? Not quite that easy as usual. It seemed close but I was still getting a frequent Service 4WD light and the buttons were acting flaky. This is actually common issue on the 99-02 truck apparently. The solder joints on the buttons need to be reflowed typically. So, I did that and changed the backlight bulbs to red LEDs to match the gauges that were done by the previous owner.

Obviously still have more backlighting that I need to change to match but no Service 4WD light and I can get 4HI at least. 4LO still isn't working which I'm not sure on at this point. But I'm calling it a success. Winter is over now so not really necessary but feels good.

Nice work. Do you have the factory wiring diagrams?

In reply to Stampie :

Kind of, I used the Autozone "Repair Guide" feature that you get if you make a free online account and it has some fairly usable wiring diagrams

KaneOconnor said:

For the NP263 problem, it could be necessary to check out the wiring or control stuff, since swaps like this can cause some confusing issues with the electronics or mechanics. Fixing the power steering and hydroboost might mean you need to figure out what's going on with the hydraulics or maybe even fix some parts. And when it comes to tuning that 6.0 engine, getting it just right could really make the truck a lot better for whatever you need it to do.

pre-canoe methinks

ever contemplate swapping in a manual shift t case?

In reply to onemanarmy :

Definitely, and that would probably be the smart thing to do. I wanted to try make it work with what I had but the miscellaneous parts probably cost as much as a manual t case and I still don't have the electronic t case working perfectly.

Your 4 low problem might be because of the fact that it was an automatic. I think my push button 4x4 will only go into 4 low if you're in park or neutral, so wonder if it's looking for some signal that's not there. Been a long time since I actually tried to use my 4 low though, so I might have that wrong.

gearheadE30 said:

Your 4 low problem might be because of the fact that it was an automatic. I think my push button 4x4 will only go into 4 low if you're in park or neutral, so wonder if it's looking for some signal that's not there. Been a long time since I actually tried to use my 4 low though, so I might have that wrong.

I started to say the same thing yesterday, but decided he probably knew that. Mine has to be running, in Neutral, and foot on the brake.

OP: Isn't the NP263 an Auto T/C, with a full-time 4wd mode? Might need a 4-button switch. But honestly, you are way ahead of my knowledge. Good luck!

In reply to gearheadE30 :

This was my first thought too. Though I don't see where the TCCM gets the neutral/park signal. I wonder if the previous owner wired the neutral safety switch to the clutch pedal? Then in theory it would shift to 4LO with the clutch in? The real issue is the push button t case never came behind the 5 speed as far as I know. So there's not really any existing information to go off of.

llysgennad : Its likely that has something to do with it. I'm just pushing the limits of my knowledge to get this far. The NP263 is the 3 button t case with just 2HI, 4HI, and 4LO. The NP246 that originally came in the truck had the full time 4wd "auto" mode. Unless I'm very mistaken...

Not that easy. Truck starts without the clutch pressed so the neutral safety was just jumped. I did notice the automatic cluster shows the gear selected as Drive. I wonder how difficult that would be to change.

On a similar route, I have a 2000 C1500. 4.3 with manual. What is involved to swap to a 5.3? New clutch flywheel and slave cylinder is expected and just good housekeeping. This unit is cable TB not electronic(DBW). I can swap any wire harnesses as needed. I've done 4.8 to 5.3 and 6.0 but that is all DBW eights. I'm just hoping someone has the history on this one. I've got access to plenty of donors here in GA. I'll swap out all the wiring if needed.  Thanks in Advance. 

Without looking too closely at your pictures, generally those modules all have some kind of connection to the backbone Class II/CAN network in the truck. Usually things like gear position, vehicle speed, etc are passed across that network. 

Was this truck retuned - as in, does the cal still have an automatic transmission segment or was it switched to a manual transmission cal or trans segment? If it's still got the automatic segment, there's probably a jumper wire somewhere in the trans harness to make it think it's in drive all the time. The stock ECM uses different maps and logic in park/neutral than in drive, so tricking it into thinking it is in neutral causes problems. Using a manual trans segment is the "right" way, but it's possible to use the auto trans segment if you disable all the trans diagnostics and eliminate all of the shift torque reduction - it just thinks it is in drive all the time. 

NP246 is the Autotrak transfer case. I'm not sure about the others.

In reply to AhBNormal :

I wouldn't be too helpful as I've never done the swap though I have looked into it. I think, don't hold me to it, the common solution for cable TB on the V8s is flashing a van OS to the PCM and using a van wiring harness but, in my research, it got kind of confusing and I only seem to learn by doing it.

In reply to gearheadE30 :

There is a serial wire to the PCM so some kind of communication is happening

The PCM is flashed as a manual transmission. So I don't know that the TCCM is even receiving the signal it would need for park/neutral as the 5 speeds never came with the push button transfer case.

In reply to white_averson :

Thanks for trying! I'll post this separately so as to not hijack this build post. Many Thanks Indeed! Cheers!

And, on the topic of the functionality of the 4WD, I got to test it in the mess we got here in New England this weekend. It worked like I need it to. Shifted properly into and out of 4HI and pulled me out of a few spots that I just spun otherwise. Will I ever need 4LO? Probably not. But I do like having all the functionality my vehicle is supposed to have.

Not a lot of exciting progress on the truck. It is the daily so gotta keep it on the road. I did finally figure out why I couldn't get the VE tuning working on HP Tuners. Turns out these older PCMs have two VE tables for some reason and if you don't edit both, nothing will change. So trying to dial tune in. Still having lean light throttle spots when I enable MAF and speed density at the same time for some reason.

I did get all the interior illumination swapped to red LED.

The crappy photos also showcase the steering wheel controls on the Escalade steering wheel the previous owner installed. Now, I would never choose to install the steering wheel myself, but now that its there, I need to make the controls work.

First problem, the clock spring doesn't have the connector for the controls, and the previous owner just cut the air bag connector off for some reason.

Next problem, the necessary clock spring is relatively rare, only being found on something like 01-02 Escalades and 99-02 Denalis? I ended up buying an entire Denali steering column for the clock spring, which ironically came with another of the same steering wheel.

I made up a wiring harness.

Removed the old clock spring.

Installed the new one.

For steering wheel wiring, black is grounded and gray goes to dimmer for illumination. I just connected it to the cargo lamp illumination wire.

And then, these might be totally normal for audio people, but I thought it was super cool there was a module that allowed OEM controls to work with a aftermarket head unit. I got this Axxess ASWC.

For wiring, typical ignition power and ground for the module, for this specific steering wheel the yellow wire goes to the yellow and green wire on the module. And the green wire from the steering wheel also goes to ignition power. I just made these connections in the radio harness with spade connectors.

Very hack looking and, as you can see, the previous owner's radio wiring is a mess. I might clean it up some day but for now I just shoved the whole mess back into the dash. But after a little fiddling with the module programming, I know have working steering wheel controls! Nothing terribly exciting but satisfying.

Next, the front alignment is jacked and before I put the bro truck wheels back on I'm going to install some Kryptonite cam bolts and get it aligned.