CIRCUIT DESCRIPTION:This DTC sets when the TCM detects no communication on the CAN1 backbone harness for a period of time. ACTION TAKEN WHEN THE DTC SETS:1. The CHECK TRANS light is not illuminated.2. DTC is stored in the TCM history.3. SEM operation is not active, if applicable.4. Default values are substituted for missing data, e.g., engine throttle percentage, engine torque, engine coolant temperature.5. The TCM freezes shift adapts (DNA). CONDITIONS FOR CLEARING THE DTC:Use the diagnostic tool to clear the DTC from the TCM history. The DTC automatically clears the DTC from the DTC history if the vehicle completes 40...

CIRCUIT DESCRIPTION:This DTC sets when the TCM detects no communication on the CAN2 backbone harness for a period of time. ACTION TAKEN WHEN THE DTC SETS:1. The CHECK TRANS light is not illuminated.2. DTC is stored in the TCM history.3. SEM operation is not active, if applicable.4. Default values are substituted for missing data, e.g., engine throttle percentage, engine torque, engine coolant temperature.5. The TCM freezes shift adapts (DNA). CONDITIONS FOR CLEARING THE DTC:Use the diagnostic tool to clear the DTC from the TCM history. The DTC automatically clears the DTC from the DTC history if the vehicle completes 40...

CIRCUIT DESCRIPTION:This test detects the loss of certain messages from the CAN Bus. ACTION TAKEN WHEN THE DTC SETS:1. The CHECK TRANS light is not illuminated.2. DTC is stored in TCM history.3. Default values are substituted for missing data, e.g., engine throttle percentage, engine torque, engine coolant temperature. CONDITIONS FOR CLEARING THE DTC:Use the diagnostic tool to clear the DTC from the TCM history. The DTC automatically clears the DTC from the DTC history if the vehicle completes 40 warm-up cycles without the DTC recurring. DIAGNOSTIC AIDS:DTC U0100 indicates that a CAN bus hardware error has occurred. This code may...

Allison 1000 & 2000 Gen 4 Fault Codes: P1688 Unmanaged 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). Unmanaged engine torque is sent from the PCM to the TCM over wire 109 (GM wire 2467). 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...

Allison 1000 & 2000 Gen 4 Fault Codes: P0122 Pedal Position Sensor Circuit Low 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...