Check Sum

[TBMSport]

Can someone explain the full calculation and control parameters of CHECKSUM? Does the ECM or TCM perform the test? Is same VIN and/or model year OS essential between ECM/TCM? Thanks

[GMPX]

The checksum is something the ECM (or TCM) does on itself when the key is turned on. Depending on the controller type depends on the complexity of it. In a nutshell it adds up a range of numbers and those numbers must equal a known value. If it doesn't then the controller assumes the flash chip has gone bad and the result will usually be limp mode or something along those lines. When you make a change to the tune with EFILive the software creates the correct 'known value' checksum.

Cheers,
Ross