Ignition Timing Control
WARNING: This page does not describe the selected car, but rather 15 other vehicles, including the 2003 Hummer H2, 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 GMC Sierra, and 2003 GMC Savana. However, it is still accessible from the selected car via links, so may be relevant.
Ignition spark timing and ignition dwell time are controlled entirely by the PCM. The PCM monitors information from various engine sensors, computes the desired spark timing and dwell, and firing of the ignition coil via ignition control circuit to the coil driver.