Freaking quote isn't working...so bear with me.


Well i got it running and driving but Im having a few issues, Ive found some information on this subject in all different types of forums, but its all scattered and hazy. Which pcm are you using?

In '04-'06 GPs the pins going to and in the pcm for the 4t65e and O2 sensor are in different locations than my stock '02 harness and pcm, makes sense with the 3 Plug PCM. 04+ pcm is totally different connectors than a 2002. Take a picture of the wiring harness connectors at the pcm please. This will tell us exactly what you are working with.

This is where im getting conflicting information.
Some people say the transmission will not work without too much work. and it would be more cost effective swapping in the correct transmission.
Depends on how you want to go about it. You could so something similar to what Rob did in this post. He swapped the channel plate, valve body, wiring harness and 4th clutches. Which could be sourced on Ebay or a junkyard pretty cheap. This also depends on which harness etc you are using. I believe you have an 04 harness though. http://www.grandprixforums.com/general-tech-discussion/69523-my-l32-swap-build-thread-20k-mile-update.html

Ive also read that you can swap pins around and add some in other places to my existing PCM and harness to get the transmission and O2 sensors to read properly. But they didnt mention what pins where. And im skeptical this will work but it would obviously be the cheapest route.Anyone know how I would go about doing that. This was definately regarding the trans only from an 02 to 04 or the other way around.

Another thing i read what this:
"Just did an analysis of the various PCM’s that the 3800SC engines used and came away with the following: My conclusion seems to agree with the information that you passed on.
The 4T65eHD’s up until 2002, all used transmission fluid pressure switches that were used to set the line pressure. In 2003 it appears that the transmission design was changed to incorporate a PC solenoid to accomplish this task.
A comparison of the PCM output diagram from 2003 to the 2004-2006 units appear to show almost identical outputs to the tranny with a couple of exceptions.
The 2004-2006 PCMs have a Remote Shift Selector signal that I believe is for the paddle shift option that the series III uses. The 2003 PCMs have a TCC Brake Switch Signal output which I don’t see on the 2004 - The 2003 PCM doesn’t output a Remote Shift Selector signal. The 2004-2006 units do.
Therefore, a couple of assumptions can be made about using a 2003 PCM series II to manage the later 4T65e HD transmissions used on the series
III You will be much better off going to either a 2002 or 2004 setup and leave the 03 info alone.



  1. It appears that the change in controlling the transmission fluid pressure was done in 2003 while the series II engine was still being used.






  1. The 2003 PCM can probably shift this transmission provided that the PW modulation or control parameter input to the PC solenoid valve HI/LO in/outs is the same as the 2004-2006 transmissions. We guess that it probably is unlikely that GM would make the change for one year only.

Negative..




  1. The Remote Shift Selector signal output is missing on the 2003 PCM (we assume paddle shift) so we will need to determine if the trans shifting defaults to automatic shifting without seeing it.
  2. Depending on what tune etc is in it will explain a lot





  1. No surprise, but the pre 2003 PCMs WILL NOT SHIFT the late 4T65EHD’s and it is very questionable even if internal mods can make the trans compatible with the earlier PCM.going to call bs on this. I've done tons of trans swaps from differing years etc. The key is the valve body/channel plate and also always replace the pump shaft with the same as the donor for the valve body/channel plate.


Ideally the next step would be to locate someone who has tried swapping the 3800SC series III /4T65eHD powertrain and running it with the 2003 GTP PCM w cable style TB and sensors. If it can be done, this would get us away from trying to install with ETC (which is something that we want to avoid). The swap would probably be successful using this powertrain with the 2003 PCM, Northstar TB, series II O2 sensors and the LS6 MAF, but a couple of questions remain before we attempt it. Seems like we may be the first folks to try it."

Source: https://zzperformance.com/96-07-gtp-model-differences. Likely written by ZZP in 2004. This stuff has been done hundreds of times. With the exception of the transmission I did this in a 97 Bonneville that I later swapped to a 99 pcm to get faster data speeds.

Has anyone Tried this before? Or know if it works or not? Will a '03 GP PCM plug into my 02 harness without modifacation? Aha.. you think you have an 02 harness! Pics still need to be done though. You can use your 02 pcm if that's what you have.

sorry for the long post. Lots of info to go over.Better to be thorough than screw stuff up.