Allison 1000 & 2000 Gen 4 Fault Codes: P0773 Shift Solenoid E Electrical CIRCUIT DESCRIPTION:Shift solenoid E is a normally closed (N/C) solenoid that provides control main pressure to stroke the E shift valve. The TCM determines the proper solenoid command logic to move the E shift valve to attain a particular range requested. A pressure switch, located at the end of the shift valve, sends shift valve position feedback to the TCM. 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...

Allison 1000 & 2000 Gen 4 Fault Codes: P0776 Solenoid B Controlled Clutch Stuck Off CIRCUIT DESCRIPTION:Trim solenoid B is used to control on-coming, off-going, and holding pressure to any one of the five clutches. This solenoid is referred to as a Pressure Proportional to Current (PPC) solenoid since the output hydraulic pressure supplied by this solenoid is proportional to the controlled current command. The Transmission Control Module (TCM) uses information from the turbine and output speed sensors to detect if a clutch is slipping. The clutch being controlled by the solenoid B will vary depending on the shift that...

Allison 1000 & 2000 Gen 4 Fault Codes: P0777 Solenoid B Controlled Clutch Stuck On CIRCUIT DESCRIPTION:Trim solenoid B is used to control on-coming, off-going, and holding pressure to any one of five clutches. This solenoid is referred to as a Pressure Proportional to Current (PPC) solenoid since the output hydraulic pressure supplied by this solenoid is proportional to the controlled current command. The Transmission Control Module (TCM) uses information from the turbine and output speed sensors to detect if a clutch is in a tie-up condition or if three clutches are applied. The clutch being controlled by solenoid B...

Allison 1000 & 2000 Gen 4 Fault Codes: P0778 Pressure Control Solenoid B Electrical CIRCUIT DESCRIPTION:Trim solenoid B is used to control on-coming, off-going, and holding pressure to any of the five clutches. This solenoid is referred to as a Pressure Proportional to Current (PPC) solenoid since the output hydraulic pressure supplied by this solenoid is proportional to the controlled current command. The solenoid operates at a very high 1000 Hz frequency. Unlike the pulse width modulated Torque Converter Clutch (TCC) solenoid, where the ball follows the pulse width square wave, the PPC ball remains stationary due to the high...

Allison 1000 & 2000 Gen 4 Fault Codes: P0840 Transmission Pressure Switch Solenoid C Circuit 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 C pressure switch monitors C shift valve positioning and relays it to the TCM. When C pressure switch is in the open state, C 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. C shift valve is...