Gearbox Input Speed Sensor (Speed Of The Input Shaft)

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Fig 1: Identifying Transmission Input Speed Sensor

Courtesy of VOLVO CARS OF NORTH AMERICA.

The gearbox input speed sensor (speed of the input shaft) is on the top of the gearbox housing. The sensor is an active sensor and is supplied with 12 V. When the pulse wheel on clutch C1 rotates, the sensor generates a pulsed current (quadratic wave) where the strength of the current depends on the position of the pulse wheel. The signals from the coils in the sensor are then affected by a magnetic resistance element, which generates a current which oscillates between 7 mA and 14 mA, and whose frequency increases with speed. Using the signal from the sensor, the transmission control module (TCM) calculates the gearbox speed, unit RPM.

The transmission control module (TCM) uses information about the input shaft speed to calculate the torque reduction to be requested from the engine control module (ECM) when shifting. The value is also used to compare the engine speed (RPM) with the speed of the input shaft in order to calculate the slipping rate of the torque converter. The value is also compared with the gearbox speed sensor signal in order to calculate the actual gear ratio. This is done to check whether the value corresponds to the expected gear ratio.

There are diagnostics for the gearbox input speed sensor.