OK, one more hail-mary...

[Shdwdrgn]

OK guys, regarding this nightmare with the gear swap and PCM programming, I have an idea to try but I want to run it through here and see if anyone can think of a reason why this wouldn't work...

I did some searching online, and found another 2004 TB SWB in a salvage yard with the GT5 gears. They were kind enough to provide the full VIN, and a picture of the glove-box RPO code sticker, verifying that it really does have the GT5 gears. Of course about half the other RPO codes differ from my own vehicle, so its not an exact match.

My question is, does it matter? Both vehicles have the 4.2 engine and are 4WD. They also both have the U68 code for the DIC (which could potentially be an issue?), so they seem to be a good match for what seems like the most critical parts.

Most importantly -- If I have someone pull the programming from this VIN and flash it into my PCM (then change the VIN in the PCM to match my vehicle again), is there any reason why I would have any problems? Would everything work like from the factory at this point? Or do any of those RPO codes signify actual changes to the programming other than minor things I could correct by copying tables back from HPTuners?

[jonbo2002]

I believe once you change the VIN to your's it would change the ratio, I may be wrong on this but your VIN is 3.42 ratio so once switched it will go back to the same problems you have now. Most don't care about the speedo matching the speed they just use a GPS to figure out their speed and go with it, at least thats all we did with my wifes Jeep.

[Trail X]

Jon, the issue is that the mismatched vss ratios from the front and rear are making his ABS and PCM angry, and throwing lights. It's not so much that he just wants to correct his speedometer.

Jeff, I'm thinking that you could get that to work. I'm trying to think if there are any other RPOs that would affect anything, and I'm not coming up with much. My only suggestion is to ask someone at PCM for less for their opinion, since that is essentially what they do.

[Shdwdrgn]

Actually I DO want to correct my speedo. What can I say, I'm picky! I want everything working like it should. Hell I spent $500 for HPTuners just so I could disable the P0420 error light.

The VIN doesn't actually decode anything about the gear ratio. It gives the body style, engine size, and brake capacity -- and those digits are all exactly the same between my original VIN and the new one I turned up. There's no way the PCM code has a complete breakdown of all VIN numbers and their features.

[jonbo2002]

the vin decodes everything about the truck. Thats how I am able to help our fellow members make sure the axle they are ordering is the correct ratio. I hate to say it though but I think the only way you can fix the speedo is if your TB was a newer year.

[Trail X]

Jonbo, it decodes it only by looking at a GM database, right? I think thats what he's talking about. There's no way that the PCM can have that same lengthy database stored inside it, can it?

[jonbo2002]

as far as I can figure the earlier models of the TB didn't have any option to program the ratio and 03 to 05 pcm's all have the same interchange so when someone orders a pcm from us we don't ask them about any of their options we just tell them the dealer has to program them for their VIN. if the delear has already told him they cannot change it, its because for some corney reason GM didn't let us have access to the ratio in the early models. I am no programer maybe someone with enough knowledge could hack into one and change the calculations but it hasen't been done yet. pcmforless even says they cant program ratios on the early years right?

[Shdwdrgn]

The way I understand it, when you pull a VCI based on the VIN, the VCI contains all the feature information for that vehicle, including the gear ratios. You drop that into the PCM, and its all pre-programmed to work with what GM believes is the equipment on your vehicle.

So what I am talking about doing is essentially pulling the VCI from a vehicle that came stock with the GT5 option, therefore the programming would already contain the information about the 4.10 gears. Once my PCM is programmed with that data, I would use HPTuners to do a simple VIN change within the PCM (NOT reprogram the whole PCM based on the different VIN). All of the GT5 gear info should still be in the PCM, but the VIN is adjusted so it matches the rest of my system.

Of course if for some reason I ever chose to take my vehicle in to GM, and if for some reason they decided to reprogram my PCM based on the VIN, I would be back to square-one... So I just need to make sure that never happens.

[jonbo2002]

ok well good luck. let us know if it works

[djthumper]

Is there any way to do comparisons between the two? It would be like comparing the codes to each other to see how they are changed...

[Shdwdrgn]

Actually I'm curious about that myself. The guy who is going to do the reprogramming for me has a bunch of different scanners, so I'm going to see if he can actually dump the whole PCM to a file for me.

[Shdwdrgn]

So I've been discussing the issue with a guy a know in Texas. Apparently GM makes a point of making it difficult or impossible to read any of the programming from the computer, so comparing files is not going to be possible with any of the equipment he has available...

I got my spare PCM sent off to him yesterday, along with the VIN that I found of a 2004 with GT5 gears. Once I get it back, I'll pop it in the truck and run with it for a bit to see if its going to work or not. If it does work, I'll register it with HPTuners and rewrite the custom tables. If it doesn't work -- I'm out of ideas.

[Shdwdrgn]

Well, he tried several things, including having the ear of the programmer for another tuning package, but alas we continue to fail at this project. My wife is out of work at the moment, so I have to watch my money again, so I haven't been able to get my extra PCM tuned to the VIN that I found which came stock with 4.10's and 4x4. Anyone else had any luck?

[Shdwdrgn]

I finally have some time and money, so I made an appointment with the dealership for April 3rd to get my extra PCM programmed to that other VIN that I found. I had actually called the salvage yard that had the vehicle, but they had already sold the PCM. So I'll get mine reprogrammed here in a couple weeks, and we'll find out if this method is going to work or not.

Wish me luck...