Automatic gearbox - Jatco (1): Description and operation (page 4 of 4)

Vehicle Speed Sensor

The vehicle speed sensor is located within the gearbox. The EAT ECU uses this sensor to monitor the rotational speed of the parking gear and calculate this reading into a vehicle speed. The EAT ECU also monitors the vehicle speed using a signal from the ABS ECU.

The vehicle speed sensor detects the parking gear rotation speed and sends an electrical output to pin 5 of the EAT ECU which also provides an earth path for the sensor.

The sensor is an inductive sensor that produces a sinusoidal output at a frequency of 18 pulses per revolution of the parking gear.

The EAT ECU uses the signal to calculate the following: l Amount of engine torque reduction required during gear changes l Notify the EAT ECU when the vehicle is stationary, for creep control.

The vehicle speed sensor can fail the following ways: l Sensor open circuit l Sensor short circuit to 12 or 5 volts l Sensor short circuit to earth.

The EAT ECU will detect sensor failure if the ABS ECU speed signal is more than 25 mph (40 km/h) but the vehicle speed sensor reading is less than 3 mph (5 km/h) for more than two seconds.

In the event of a vehicle speed sensor signal failure any of the following symptoms may be observed: l Upshift to 5th gear inoperative l Torque reduction request from the EAT ECU to the ECM inoperative.

If a failure of the vehicle speed sensor occurs and the ABS ECU speed signal is functional, the EAT ECU will control gear shifting using the ABS ECU signal.

If both the vehicle speed sensor and the ABS ECU speed signals fail, the EAT ECU will lock the gearbox in fourth gear (fail-safe mode) and inhibit torque converter lock-up control.