T87A TCM Swap - new unlocked TCM

Guys,

Getting a bit frustrated, hoping for some help...

I got a new T87A TCM for my Sierra w/8 speed. I ordered new so I can just swap it.

It came in today, I followed the steps on the paper to replace the TCM.

When it went to copy the info from the stock TCM to the new TCM I got an error:

"TCM replacement complete. Some data was not able to be programmed. You may need to re-run the function for the new TCM if the vehicle does not run properly."

So, what next?

I tried to re-run, same result.

I then tried to read it and I did not get a screen shot - but it basically said the TCM was unreadable, here is a stock file to save.

Any advice, please? I thought this was going to be simple...

Also - I assume I can just put the factory TCM back in and be back to normal?

After a bunch of what felt like useless searched with omitted acronyms I found this:

https://forum.hptuners.com/showthrea...vehicle-pop-up

So it looks like the 2nd error is normal, but not sure about the first and what was not copied over.

The main question I have - what does the "replace TCM" tool do?

What info is it copying? What did I risk losing? The truck ran fine from what I can tell.

It says to rerun the tool, so curious if rerun is not going back to factory and just repeating the steps. The direction really don't give a lot of info on the paper that came with the TCM, the help files or the warning that popped up. Not sure if this is something to be concerned over.

Update - HPT support said having the scanner logging at the time could cause issues. I went back through the steps (added some more notes vs. what support sent):

1) Delete the contents within "Modules" folder located at ("...\Documents\HP Tuners\VCM Scanner\Modules")
2) Re-installed stock program in new TCM
3) Key off, re-installed the STOCK TCM
4) Key on, engine off
5) Connect VCM Scanner to the vehicle by clicking the "Connect to Vehicle" button, NOT the "Start Scanning" button
6) If you are seeing values appear in the channels window or the gauges window, stop the datalogging by hitting the "Stop Scanning" button on the toolbar
7) Run the "Replace TCM" function from the "Vehicle Controls & Special Functions" menu (I forget the tab name, under system or something, I am not connected to the truck right now)
8) Follow the prompts to complete the "Replace TCM" function for the STOCK TCM
9) Stop scanner and turn off the ignition
10) Re-install the UNLOCKED TCM
11) Key on, engine off
12) Connect VCM Scanner to the vehicle by clicking the "Connect to Vehicle" button, NOT the "Start Scanning" button
13) If you are seeing values appear in the channels window or the gauges window, stop the datalogging by hitting the "Stop Scanning" button on the toolbar
14) Run the "Replace TCM" function from the "Vehicle Controls & Special Functions" menu (same way as above)
15) Follow the prompts to complete the "Replace TCM" function for the UNLOCKED TCM. You will tell it this is not the stock TCM, then the next screen will be the selection to copy to the new TCM, at least mine was

Here is where you expect it to go through and I was having issues. Stopping the scanner did not seem to help.

I went through the first time and I got that same error message, complete but may have lost data. While the key was still on I restarted the function while it was still connected to the vehicle. I got the same error message again. I tried again, same error message (I think, not sure if I got it 2 or 3 times). The 3rd or 4th try it said complete and to cycle the ignition.

I am waiting to hear from support to confirm everything is good. The truck did run fine before doing this with the error. One main note is after this went through I re-read the TCM and there were some new general tables that popped up and the manual tab had tables it did not have before. None of these selections were anything I would change (like gear ratio, CAGS, etc.).

So the error message does in fact cause issues when pulling the tune file to work off of. When I get the response from support I will update this in hopes someone else can search and get a quick answer if they come across the same issue. I thought the new TCM was simply a swap, I didn't realize it until I saw the instructions I had to go through this special function.

FWIW - I did the fast learn on the tranny with the special functions too. I think that really helped accelerate the adaptation. It may be all in my head, but I did make one drive before doing that and it definitely had a few hiccups like flares between the gears I did not see the first time I installed the new TCM and did fast learn. After about 20 miles of mixed driving and stabs at the throttle, it really feels a lot better now.

I actually think the difference in the new read was the fact that I read the TCM and ECM at the same time, last time was TCM only.

Good info.

Good information. I just had a TCM unlocked and programmed and got no instructions like this.

Thanks for sharing this info

I had this issue with a 2018 ZL1. But the car wouldn't shift out of park and then when it finally did there were some no shifting issues. After going round and round with support, we put everything back to stock programming, returned the unlocked TCM, and sent the cars original TCM to HPTuners to be unlocked. Once the original TCM came back unlocked, we flashed the TCM with out any further issues. Never really had any resolution of the issue so I try to avoid buying an "extra" TCM for the 2018+ cars from my experience.

If I am in this situation again I will read both the ECU and TCM together. IIRC I only did the TCM because we had already built the car and tuned the ECU.

Do you have to remove the battery negative cable between ( removing stock TCM and installing the new unlocked TCM ) ?

I can?t say I did it the right way, but I?m pretty sure I just removed the connector and unplugged it with the battery still connected.

It might not be right, but the truck still runs lol

Thanks for the reply man.
Good to know that you’re car runs good.

I can’t find a direct guide to do TCM T87A swap, I mean direct and clear info.
The info with the new TCM is not enough.