Allison 1000 & 2000 Gen 4 Fault Codes: P0708 Transmission Range Sensor Circuit High Input CIRCUIT DESCRIPTION:The installation of a transmission-mounted Neutral Start/Back-Up (NSBU) switch is required. This switch mounts directly onto the transmission housing from the outside and detects the angular position of the shift selector shaft. This position is communicated to the Transmission Control Module (TCM) so that certain vehicle control functions can be coordinated with the position of the shift controls. The NSBU switch has redundant circuitry to alert the TCM in the event of a single wire or switch failure. The neutral signal output of the...

Allison 1000 & 2000 Gen 4 Fault Codes: P0711 Transmission Fluid Temperature Sensor Circuit Performance CIRCUIT DESCRIPTION:The Transmission Fluid Temperature (TFT) sensor is part of the Pressure Switch Manifold (PSM) which is located in the transmission oil pan. The TFT sensor is a thermistor that changes its resistance value based on the temperature of the transmission fluid. The Transmission Control Module (TCM) supplies a 5V reference signal to the TFT sensor and measures the voltage drop in the circuit. When the transmission is cold, the sensor resistance is high and the TCM detects high signal voltage. As the transmission fluid...

Allison 1000 & 2000 Gen 4 Fault Codes: P0712 Transmission Fluid Temperature Sensor Circuit Low Input (High Temperature) CIRCUIT DESCRIPTION:The Transmission Fluid Temperature (TFT) sensor is part of the Pressure Switch Manifold (PSM) which is located in the transmission oil pan. The TFT sensor is a thermistor that changes its resistance value based on the temperature of the transmission fluid. The Transmission Control Module (TCM) supplies a 5V reference to the thermistor. The TCM’s internal impedance provides resistance at the TCM so that voltage drop can be measured between the TCM and the thermistor. When the transmission is cold, the...

Allison 1000 & 2000 Gen 4 Fault Codes: P0713 Transmission Fluid Temperature Sensor Circuit High Input (Low Temperature) CIRCUIT DESCRIPTION:The Transmission Fluid Temperature (TFT) sensor is part of the Pressure Switch Manifold (PSM) which is located in the transmission oil pan. The TFT sensor is a thermistor that changes its resistance value based on the temperature of the transmission fluid. The Transmission Control Module (TCM) supplies a 5V reference to the thermistor. The TCM’s internal impedance provides resistance at the TCM so that voltage drop can be measured between the TCM and the thermistor. When the transmission is cold, the...

Allison 1000 & 2000 Gen 4 Fault Codes: P0716 Turbine Speed Sensor Circuit Performance CIRCUIT DESCRIPTION:The speed sensors are variable reluctance devices which convert mechanical motion to an AC voltage. Each sensor consists of a wire coil wrapped around a pole piece that is adjacent to a permanent magnet. These elements are contained in a housing which is mounted adjacent to a rotating ferrous member. Two signal wires extend from one end of the housing and an exposed end of the pole piece is at the opposite end of the housing. The permanent magnet produces lines of flux around the...