Speed Sensor, Input Shaft

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Fig 1: Identifying Input Shaft Speed Sensor

Courtesy of VOLVO CARS OF NORTH AMERICA.

The speed sensor for the input shaft is located inside the gearbox. The sensor is a so-called "active sensor" (Hall sensor) and is supplied with 12 V power. When the pulse wheel on clutch C2 rotates the sensor generates a pulsed current (square wave), where the strength of the current depends on the position of the pulse wheel. The signals from the coil in the sensor are then acted on by magnetic-sensitive resistance, which means that the output signal is a current which fluctuates between 7 mA and 14 mA, and whose frequency increases with speed. The Transmission Control Module (TCM) calculates transmission speed using the signal from the sensor.

The Transmission Control Module (TCM) uses information on input shaft speed for:

calculating how much torque reduction shall be requested from the Engine Control Module (ECM) with gearshifting
comparing engine speed with input shaft speed to calculate the slipping speed of the torque converter
calculating gearshift timing
calculating engagement and disengagement of the lock-up function
comparing the signal with the signal from the transmission speed sensor for the output shaft, for calculating the current gear ratio. This is performed to identify whether the value corresponds with the expected gear ratio.

The speed sensor for the input shaft can be diagnosed.