GM Electronic Spark Control
General Motors ESC System is used for controlling pre-ignition (spark knock, pinging, etc.) by using a sensor mounted to the cylinder block that will sense vibration during times of pre-ignition.The sensor converts the vibration it senses to an electrical signal and sends it off to the ESC module. The module keeps a circuit high to the PCM as long as there is no signal from the knock sensor. When a signal enters the module from the knock sensor, the high circuit to the PCM is pulled low and the PCM will retard timing until it goes high again.
Here are the two signals with key-off, engine-off (A) knock sensor, (B) High circuit to PCM.
This is with engine at idle no-knock present.
This is engine at idle and one major tap on the intake manifold.