P1779

ALLISON AUTOMATIC TRANSMISSION

DTC P1779





Circuit Description for Allison Automatic Transmission
The Transmission Control Module (TCM) receives input from the Engine Control Module (ECM) on Throttle Knockdown Signal Circuit connector C1 pin 9 for unmanaged gross engine torque, and Delivered Torque Signal Circuit connector C1 pin16 for managed net engine torque. The TCM monitors and compares the engine input torque signals for proper torque requested values. The TCM sends a signal via Requested Torque Signal Circuit connector C1 pin 22 to the engine if a torque reduction is needed. DTC P1779 is a type X DTC for the 6.6 L engine and a type B DTC for the 8.1 L engine.

Conditions for Running the DTC
^ The components are powered and ignition voltage is greater than 9 V and less than 18 V.
^ Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.
^ Pulse Width Modulation (PWM) driver demand torque option is selected in transmission calibration.
^ DTC P1779 must not be active.

Conditions for Setting the DTC
DTC P1779 is set if managed net engine torque signal is under 1.5 percent for 2 seconds or over 98.5 percent for 2 seconds.

Action Taken When the DTC Sets
Value is defaulted with an unmanaged engine torque value. If P1688 and P1779 are active, value is defaulted with a look-up torque value based on throttle and engine speed. If P1688 and P1779 are active and throttle is defaulted and U1016 or U1300 or U1301 is active, TCC is disengaged and inhibited.

Conditions for Clearing the MIL/DTC
A scan tool can clear the code from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

Test Description
The number below refers to the step number on the diagnostic table.
2. This step tests for opens/shorts in input connector C1 pin 16 (Delivered Torque Signal circuit.