Stock (Cruze) OS: 12656286
Stock Service Number: 12643636
Stock Tune: E78 Stock.ctz

Replacement ECM OS: 12654014
Replacement ECM Service Number: 12643636
Replacement ECM Tune: New ECM Stock.ctz

Here is a comparison photo of the two ECMs:
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Here’s the story: I have a 2014 Chevy Cruze with the LUV (1.4L) and a decent tune sitting on my computer waiting to be flashed. I purchased a brand new E78 ECU with the same service number (12643636) assuming that I would be able to full flash to my car’s stock OS and the tune I have written for it.

The ECU showed up in the mail today, I installed it in the car, and read out the OS (mainly out of my own curiosity). It came with OS 12654014 (New ECM Stock.ctz, attached), which appears to be for a 6.0L. It came without the VIN programmed, which makes since because it is a new ECM.

Curiosity satisfied, I proceeded to license the ECM to my V2. It is important to note here that I attempted to license the ECU using my Cruze’s OS 12656286 (E78 Stock.ctz, attached). It returned the error $0540: Incompatible Operating System (see screenshot below). I could see this being an issue if I were attempting to do a cal flash, but I was attempting to license the controller through the full flash option.

Click image for larger version. 

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I opened the OS that came on the ECM (12654014) and selected the “Check License” option. Everything checked out fine and the terminal indicated that it was eagerly awaiting my license (see screenshot below).

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The source of my concern is this: I don’t know for sure if my Cruze’s OS is compatible with the new ECU I bought, even though the service number is identical. I don’t want to license the ECM to my V2 and then not be able to flash in my Cruze’s OS and flush the $125 down the drain (unless anybody wants to kindly donate a 6.0L to me ).

If I license the ECM, will I then be able to flash in the other OS, or will it remain “incompatible”? If anybody has any advice or experience with this please let me know. This is my first time doing an OS swap on a newer GM ECU. I’ve only dealt with LS1B and Duramax PCM/ECMs in the past and I don’t want to screw anything up.