Allison 1000 & 2000 Gen 4 Fault Codes: P0123 Pedal Position Sensor Circuit High Voltage CIRCUIT DESCRIPTION:The Transmission Control Module (TCM) receives input on throttle position from either a Throttle Position Sensor (TPS) or a signal transmitted by the engine electronic controls. Vehicles not equipped with electronically-controlled engines have a TPS attached to the engine fuel control linkage. The TPS continuously sends the exact throttle position to the transmission TCM. The TPS is a sliding resistor sensor (potentiometer) actuated by a mechanical linkage. The TCM delivers a constant voltage to one terminal of the TPS resistive strip. The other TPS...

Allison 1000 & 2000 Gen 4 Fault Codes: P0218 Transmission Fluid Over Temperature Condition CIRCUIT DESCRIPTION:The flow of transmission fluid starts in the transmission pan. Fluid is then drawn through the filter and internal passages into the oil pump assembly. The oil pump pressurizes the fluid into main-pressure that is regulated at the main-pressure regulator valve. From this point, fluid is directed to the F trim solenoid and to the control-main regulator and control-main relief valve into the control-main filter assembly and on to all solenoids for use as control pressure. Hot fluid leaving the torque converter is routed through...

Allison 1000 & 2000 Gen 4 Fault Codes: P0561 Unrealistic Variations in Vehicle System Voltage CIRCUIT DESCRIPTION:The Transmission Control Module (TCM) requires a switched ignition voltage input and a direct battery voltage input. This switched ignition voltage signal originates from the ignition switch or an ignition relay to supply voltage to pins 102 and 104 in the J1 connector at the TCM. Battery direct voltage is supplied to pin 103 at the J1 connector. CONDITIONS FOR RUNNING THE DTC:1. The test becomes enabled when the engine has been running above 400 rpm for at least 0.5 seconds.2. The components are...

Allison 1000 & 2000 Gen 4 Fault Codes: P0562 System Voltage Low CIRCUIT DESCRIPTION:The Transmission Control Module (TCM) requires a switched ignition voltage input to operate. This switched ignition voltage signal originates from the ignition switch or an ignition relay to supply voltage to pins 102 and 104 in the J1 connector at 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 less than 32V (24V TCM).2. The engine speed is greater than 450 rpm for 10 seconds. CONDITIONS FOR...

Allison 1000 & 2000 Gen 4 Fault Codes: P0563 System Voltage High CIRCUIT DESCRIPTION:The Transmission Control Module (TCM) requires a switched ignition voltage input to operate. This switched ignition voltage signal originates from the ignition switch or an ignition relay to supply voltage to pins 102 and 104 in the J1 connector at the TCM. CONDITIONS FOR RUNNING THE DTC:1. The engine speed is greater than 450 rpm for one second.2. 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). CONDITIONS FOR...