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Swapping Global A Modules in G.M.'s
Posted to Technical Discussion Forum on 11/21/2014 37 Replies

Having just read a post about swapping Global A modules, I see that most techs know that they shouldn't, but don't know why.

Global A vehicles use a vehicle specific environment identifier to prevent module swapping. Not all modules use the identifier. The IPC, EBCM, HVAC, SDM, and ECM usually always do. Each of these modules will have learned the digital identifier during initial configuration.

In operation, the BCM is the controller of the environment identifier. It sends the identifier over serial data as a challenge. The modules respond by comparing the internally stored ID against the ID sent by the BCM. If they match, the modules send the ID back to the BCM over the data line. Depending on programming, the BCM may have to see one or several incorrect responses from the modules to take action. At this point, the BCM will disable starting and the modules will set B3902 for incorrect identifier received.

When the modules receive a correct identifier after the problem is rectified, they are supposed to clear the B3902 and restore normal operation. In the real world, this doesn't always happen. The modules may lock on the incorrect ID and become permanently inoperable.

I have a 2013 Malibu with 110 miles in my bay right now. The HVAC, IPC, SDM and BCM are setting B3902 as current and the BCM is setting C0775. Guess what's wrong with it!

Don't mess with used Global A modules. It's a crapshoot that will come back and bite you!

James from Florida

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