The speedometer in a car with an automatic transmission may work as follows:
1. Output shaft speed sensor:
– The speed sensor is installed on the output shaft of the automatic transmission.
– It detects the rotation of the shaft, converting it into an electrical signal.
2. Transmission Control Module (TCM):
– The TCM receives an electrical signal from the speed sensor.
– It interprets the signal and determines the speed of the car.
3. Engine Control Unit (ECU):
– The ECU can receive speed data from the TCM.
– It uses this data to adjust engine operation according to vehicle speed.
4. Speedometer:
– The speedometer is connected to the ECU.
– It displays the vehicle speed using data received from the ECU.
Some vehicles may use a wheel speed sensor (WSS) instead of an output shaft speed sensor. This sensor is installed on the drive wheel hub and detects its rotation. The signal from the WSS is sent to the TCM or ECU where it is processed and used to determine vehicle speed.
Additionally, some vehicles may use GPS systems to determine vehicle speed, which provide a measurement independent of the automatic transmission.