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Transmission Speed Sensors
Transmission speed sensors are used to perform a contactless scan of a gear or trigger wheel in the transmission and generate an electronic digital signal proportional to the speed of rotation. There are commonly two speed sensors that work in conjunction to provide accurate transmission data to the vehicle’s (ECM) engine control module or (TCM) transmission control unit.
The first is known as the input shaft speed (ISS) or primary sensor. This sensor is used to monitor the speed of the transmission’s input shaft. The second sensor is the output shaft speed (OSS) or secondary sensor. If either of these two sensors falls out of alignment or experiences electrical issues, it can affect the operation of the entire transmission. When the ECM receives the correct information from the transmission speed sensors it is then able to calculate the optimal gear for efficient driving at that speed. If the desired gear and the actual gear do not match, then the ECM may log a diagnostic trouble code (DTC).
Common symptoms of a faulty sensor include:
- Harsh or irregular shifting
- Cruise control inoperative
- Check engine light illuminated
- Speedometer inoperative
Transmission speed sensors can malfunction for a number of reasons including:
- Physical damage to the sensor
- Poor connection between the connector plug and sensor
- Electrical failure
Without a valid speed signal from a working sensor, the ECM will not be able to correctly control the shifting of gears within the transmission. This may cause the transmission to shift quicker or harsher than normal. It's also common that a problem with these sensors can impact the shift timing, extending the interval between transmission shifts. An automatic transmission is hydraulically controlled and designed to shift smoothly. When the transmission shifts hard, it can damage internal components including valve bodies, hydraulic lines, and in some cases mechanical gears.
If you have discovered a faulty transmission speed sensor, the Goss range of aftermarket transmission speed sensors is now available and suits over 800 vehicle applications and 4 million vehicles on road. Offering the aftermarket a truly genuine alternative when searching for quality products.
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