Note. For circuit reference, see DTC P0441 schematic.
Circuit Description
PCM contains Output Driver Modules (ODMs) that provides 7 switchable ground outputs for operating solenoids, relays, indicator lights, and other devices. Each of these ground outputs has fault lines that feed back to the PCM's microprocessor. When the output is off, the output driver should receive the 12 volts fed to the solenoid, relay, etc. When the output is on, it should receive zero volts, since it is grounding the output. If PCM sees zero volts when the output is off or 12 volts when the output is on, it sets a fault line low.
DTC P1644 is used to monitor the fault line of the delivered torque output to the EBTCM. The EBTCM sends ignition voltage on the delivered torque PWM output circuit to the PCM. The PCM will then rapidly pulse this circuit to ground creating a Pulse Width Modulated (PWM) signal, indicating the percentage of torque output the engine is producing. The EBTCM uses this PWM signal for traction control.