In this video we look at how the GM PCM controls the ignition timing being delivered to the engine. We look at how to use the HP Tuners VCM Scanner software to find exactly where in the ignition tables the PCM is accessing, and how the final ignition advance is modified by the various correction tables. We also discuss the knock control system and the interaction between the high and low octane tables. This is essential knowledge for anyone wanting to reflash GM vehicles on the HP Tuners platfor