Information on converting P10 to P12

Shdwdrgn

Original poster
Member
Dec 4, 2011
568
My search-fu is failing badly right now. I've run across some threads mentioning that several people have successfully converted their P10 to a P12 PCM, but I can't seem to find the discussions of HOW it was done. Can anyone point me in the right direction?

The basis of this search is that I recently converted my axles to 4.10 gears. My local dealership has been calling the GM tech line, and GM is insisting that there is no info in their system to build a new PCM for my body style (2004 TB LT, SWB), even though they do agree that it was an available factory option. I've been chasing this problem for about a month now, and still have made no progress in getting it resolved.

So a couple of questions about this, that maybe someone can answer? Just HOW different is the code between each vehicle? GM makes it sound like they have to write custom software for each individual vehicle based on all the installed options, however I thought the PCM simply controlled the powertrain, and all of these vehicles (02-05) have the same I6 installed. How does someone like PCM4Less send me a generic PCM and have it "just work"? Could I actually find another PCM from the same year/body that was programmed for the 4.10 gears, change the VIN with HPTuners, and have it work?

And moving forward with my original question, if I upgraded to a P12, which does have all the options available in HPT for setting the gears and adjusting the speedometer, would I have to get any special programming done on it to work with my older vehicle, or could I simply drop it in (after changing connectors of course), update the VIN, and it would work? Considering the amount of time I've put into this already, and the lack of drivetrain support for the P10, I'm really thinking a conversion might be the preferred way to go (assuming there aren't any *gotchas* that I'm not aware of).
 

bobdec

Member
Apr 19, 2013
233
They are NOT plug and play swapable, MAF, CAN Protocol, serial data bus protocol. P12 is almost a must for turbo, but requires customized harness wiring alterations to go into a '02-05 . Do you have HPTuners VCM Suite or Editor the '04 has a 'transmission output revolutions per/mile' setting in the speedometer section that will adjust for any rear end changes. Take you tires rev/mile and calculate in the rear gearing to get tranny tailshaft rev/mile.
 

Shdwdrgn

Original poster
Member
Dec 4, 2011
568
Yeah I knew the two PCMs have different plugs on them, but the few threads I've found have suggested that the wires tend to match up pin-for pin, so its just the tedious task of pulling apart each connector and rebuilding all the wires into the new connector.

I'm not sure where you got the idea that its so simple to change the gear settings in the 02-05, but it is definitely NOT. The values have some slight affect on what speed the PCM believes the truck is going, but will have no change at all on the speedometer reading, nor on the ABS circuit. I can't even seem to find a GM tech willing to throw together a new PCM build for me with the correct values, even though my dealership has made multiple calls to them attempting to get it done. They have been flat-out told that GM can't build the code for my vehicle, despite the fact that this was a factory option.
 

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