Allison 1000 & 2000 Gen 4 Fault Codes: P0746 Solenoid A Controlled Clutch Stuck Off CIRCUIT DESCRIPTION:Trim solenoid A is used to control on-coming, off-going, and holding pressure in any one of five clutches. This solenoid is referred to as a Pressure Proportional to Current (PPG) 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 A will vary depending on the shift that is...

Allison 1000 & 2000 Gen 4 Fault Codes: P0747 Solenoid A Controlled Clutch Stuck On CIRCUIT DESCRIPTION:Trim solenoid A 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 (PPG) 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 3 clutches are applied. The clutch being controlled by solenoid A...

Allison 1000 & 2000 Gen 4 Fault Codes: P0748 Pressure Control Solenoid A Electrical CIRCUIT DESCRIPTION:Trim solenoid A 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 pressure output is proportional to the amount of controlled current commanded by the TCM. 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...

Allison 1000 & 2000 Gen 4 Fault Codes: P0763 Shift Solenoid C Electrical CIRCUIT DESCRIPTION:Shift solenoid C is a normally closed (N/C) solenoid that provides control main pressure to stroke the C shift valve. The TCM determines the proper solenoid command logic to move the C 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: P0768 Shift Solenoid D Electrical CIRCUIT DESCRIPTION:Shift solenoid D is a normally closed (N/C) solenoid that provides control main pressure to stroke the D shift valve. The TCM determines the proper solenoid command logic to move the D 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...