Allison 1000 & 2000 Gen 4 Fault Codes: P1779 Engine Torque Delivered To TCM Signal

CIRCUIT DESCRIPTION:
The GM 8.1 liter gasoline engine is used in some medium duty applications. The 8.1 liter engine uses a 3-wire system to communicate engine torque data/requests between the powertrain control module (PCM) and the transmission control module (TCM).

Managed engine torque is sent from the PCM to the TCM over wire 116 (GM wire 464).

CONDITIONS FOR RUNNING THE DTC:
1. The components are powered and ignition voltage is greater than 9V and less than 18V (12V TCM).
2. Engine speed is greater than 200 rpm and less than 7500 rpm for 5 seconds.
3. Pulse Width Modulation (PWM) driver demand torque option is selected in transmission calibration.
4. No DTC is active at the time of this test.

CONDITIONS FOR SETTING THE DTC:
DTC P1779 sets if managed engine torque (net) signal (circuit 464) is under 1.5 percent or over 98.5 percent for more than a 2 second period.

ACTION TAKEN WHEN THE DTC SETS:
1. DTC P1779 is stored in the TCM history.
2. The CHECK TRANS light illuminates on the second occurrence.
3. The TCM defaults to a calculated managed torque (net) input value using throttle and engine speed.
4. The TCM defaults to a calculated unmanaged torque (gross) input value using throttle and engine speed.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool may be used to 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 the DTC recurring.

DIAGNOSTIC AIDS:
An Intermittent condition may be the cause of the problem. Return the vehicle to the OEM for further troubleshooting.