The procedure used to lock a PCM is very simple, as is the seed/key algorithm.
The PCM has a combination of one seed and one key stored in flash memory. When a programming device requests read/write access to the flash chip, the PCM first sends a seed to the device. The software must calculate the key and send it to the PCM.
If the key matches what the PCM has then grants access to the flash contents.
A tuning software can change the stored seed/key to another unknown value which can only be calculated by the same cable. It uses a different algorithm so no other programming device will be able to generate the correct key, thus preventing read/write access to the flash memory. Not even the dealer can unlock a tunerlocked PCM
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