P1644

Circuit Description

The PCM contains chips called Output Driver Modules that provide 7 switchable ground outputs for operating solenoids, relays, telltales, and other devices. Each of these ground outputs has an internal fault line that feeds back to the PCMs 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 0 volt since it is grounding the output. If it receives 0 volt when the output is OFF or 12 volts when the output is ON, it sets the fault line low. DTC P1644 is used to monitor the fault line of the delivered torque output to the Electronic Brake and Traction Control Module (EBTCM). The EBTCM sends ignition voltage on CKT 464 to the PCM, the PCM will then rapidly pulse CKT 464 to ground creating a Pulse Width Modulated signal that indicates the percentage of torque output the engine is producing. The EBTCM uses this PWM signal for traction control.

Conditions for Running the DTC

^ Brakes not applied.
^ PCM in Closed Loop fuel control.

Conditions for Setting the DTC

Fault line is low for 2.5 seconds.

Action Taken When the DTC Sets

^ The Malfunction Indicator Lamp (MIL) will not illuminate.
^ No message will be displayed.

Conditions for Clearing the DTC

^ A History DTC will clear after forty consecutive warm-up cycles with no failures of any non-emission related diagnostic test.
^ A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.
^ Use a scan tool to clear DTCs.
^ Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended.

Diagnostic Aids

Check for an intermittent poor connection at both the PCM and the EBTCM or an open or short in CKT 464.