DTC P0650: Mil Control Circuit: Description
WARNING: This page is about a different car, the 2001 GMC Savana, 2001 Chevrolet RV Cutaway, 2001 Chevrolet Cutaway, and 2001 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
Ignition voltage is supplied directly to Malfunction Indicator Lamp (MIL). Powertrain Control Module (PCM) controls light by grounding control circuit via an internal switch called a driver. Primary function of driver is to supply ground for component being controlled. Each driver has a fault line which is monitored by PCM. When PCM is commanding a component on, voltage of control circuit should be low, about zero volts. When PCM is commanding control circuit to a component off, voltage potential of circuit should be high, about battery voltage. If fault detection circuit senses a voltage other than what is expected, fault line status will change causing DTC P0650 to set.