Speed Sensors
The vehicle speed sensor is a device that is mounted on the output shaft of the transmission or transaxle. This device tells the electronic control module (ECM) how fast the vehicle is moving. It consists of a wheel with teeth around it and a magnetic pickup. The wheel can either be attached to the output shaft or be gear driven off the output shaft. As the wheel is turned, it induces an alternating current (AC) in the magnetic pickup. The ECM uses this information to calculate how fast the vehicle is moving.
Shift Solenoids
Electronic transmissions utilize shift solenoids to control when the transmission will shift from one gear to the next. The solenoid affects hydraulic pressure on one side of a shift valve, causing it to move. In some transmissions this solenoid is connected directly to a check ball that acts as a shift valve. Energizing the shift solenoid causes the check ball to move and either open or close pressure passages leading to the holding members. The ECM works with the shift solenoids, either receiving or sending input to tell the solenoid to operate or hold. If the speed is appropriate for an upshift, however, the throttle position sensor tells the ECM it is wide open; under a heavy load, for example, the ECM may hold the shift solenoid from operation until the throttle is changed.
