P1779

ALLISON AUTOMATIC TRANSMISSION

DTC P1779
Circuit Description for Allison Automatic Transmission
Vehicles currently using the 8.1L gas engine use a 3 wire system to communicate engine torque data/requests between the powertrain control module (PCM) and the transmission control module (TCM).

DTC P1779 is a type B DTC.

DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1779 Torque Delivered Signal

Conditions for Running the DTC
^ Components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
^ 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.

Conditions for Setting the DTC
DTC P1779 sets if managed engine torque, net, signal is less than 1.5 percent, or greater than 98.5 percent for greater than 2 seconds.

Action Taken When the DTC Sets
^ The TCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
^ DTC 1779 is stored in TCM history.
^ The TCM defaults to a calculated managed torque, net, input value using throttle and engine speed.
^ The TCM defaults to a calculated unmanaged torque, gross, input value using throttle and engine speed.
^ The TCM inhibits torque converter clutch (TCC) engagement.

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

Diagnostic Aids
^ Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions:
- A bent terminal
- A backed-out terminal
- A damaged terminal
- Poor terminal tension
- A chafed wire
- A broken wire inside the insulation
^ When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
^ You may have to drive the vehicle in order to experience a condition.

Test Description





The numbers below refer to the step numbers on the diagnostic table.
2. This step tests for a damaged terminal or connector.
4. This step tests for an open/short.