Allison 1000 & 2000 Gen 4 Fault Codes: P0873 Transmission Pressure Switch Solenoid E Circuit High CIRCUIT DESCRIPTION:The Pressure Switch Manifold (PSM) is a multiple-switch assembly made up of three normally open (N/O) and one normally closed (N/C) pressure switches. The E pressure switch monitors E shift valve positioning and relays it to the TCM. When E pressure switch is in the open state, E shift valve should be in the destroked position. CONDITIONS FOR RUNNING THE DTC:1. Components are powered and the ignition voltage is greater than 5V.2. DTC P0561, P0562, or P0563 is not active.3. E shift valve...

Allison 1000 & 2000 Gen 4 Fault Codes: P0875 Transmission Reverse Pressure Switch Circuit Malfunction CIRCUIT DESCRIPTION:The Pressure Switch Manifold (PSM) is a multiple switch assembly made up of three normally open (N/O) and one normally closed (N/C) pressure switches. Fluid pressure is supplied to the reverse pressure switch, holding it open, when the manual selector valve is in any position except reverse. When the manual selector valve is moved to Reverse, pressure to the reverse pressure switch is cut off, allowing the switch to close. CONDITIONS FOR RUNNING THE DTC:1. The components are powered and ignition voltage is greater...

Allison 1000 & 2000 Gen 4 Fault Codes: P0876 Transmission Reverse Pressure Switch Circuit Stuck Open CIRCUIT DESCRIPTION:The Pressure Switch Manifold (PSM) is a multiple switch assembly made up of three normally open (N/O) and one normally closed (N/C) pressure switches. Fluid pressure is supplied to the reverse pressure switch, holding it open, when the manual selector valve is in any position except reverse. When the manual selector valve is moved to Reverse, pressure to the reverse pressure switch is cut off allowing the switch to close. CONDITIONS FOR RUNNING THE DTC:TFT is greater than 0°C (32°F). DTC P0706, P0708,...

Allison 1000 & 2000 Gen 4 Fault Codes: P0880 TCM Supply Voltage CIRCUIT DESCRIPTION:DTC P0880 sets if an abnormal power-down sequence has occurred. This condition means the Transmission Control Module (TCM) has lost supply voltage (wire 103) before it has finished saving information from that drive cycle. This process is usually completed in less than 10 seconds. CONDITIONS FOR RUNNING THE DTC:1. The components are powered and ignition voltage is greater than 9V and less than 18V (12V TCM) or greater than 18V and less than 32V (24V TCM).2. Loss of TCM supply voltage before drive cycle data is saved....

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...