Transmission Speed Sensor: Description and Operation
SPEED SENSOR INPUTDESCRIPTION
The Input Speed Sensor is a two-wire magnetic pickup device that generates AC signals as rotation occurs. It is threaded into the transaxle case (Fig. 310), sealed with an O-ring (Fig. 311), and is considered a primary input to the Transmission Control Module (TCM).
OPERATION
The Input Speed Sensor provides information on how fast the input shaft is rotating. As the teeth of the input clutch hub pass by the sensor coil (Fig. 312), an AC voltage is generated and sent to the TCM. The TCM interprets this information as input shaft rpm.
The TCM compares the input speed signal with output speed signal to determine the following:
- Transmission gear ratio
- Speed ratio error detection
- CVI calculation
The TCM also compares the input speed signal and the engine speed signal to determine the following:
- Torque converter clutch slippage
- Torque converter element speed ratio
SPEED SENSOR OUTPUT
DESCRIPTION
The Output Speed Sensor is a two-wire magnetic pickup device that generates an AC signal as rotation occurs. It is threaded into the transaxle case (Fig. 318), sealed with an O-ring (Fig. 319), and is considered a primary input to the Transmission Control Module (TCM).
OPERATION
The Output Speed Sensor provides information on how fast the output shaft is rotating. As the rear planetary carrier park pawl lugs pass by the sensor coil (Fig. 320), an AC voltage is generated and sent to the TCM. The TCM interprets this information as output shaft rpm.
The TCM compares the input and output speed signals to determine the following:
- Transmission gear ratio
- Speed ratio error detection
- CVI calculation
VEHICLE SPEED SIGNAL
The vehicle speed signal is taken from the Output Speed Sensor. The TCM converts this signal into a pulse per mile signal and sends it to the PCM. The PCM, in turn, sends the vehicle speed message across the communication bus to the BCM. The BCM sends this signal to the Instrument Cluster to display vehicle speed to the driver. The vehicle speed signal pulse is roughly 8000 pulses per mile.