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3 Signs of a Failing Transmission Speed Sensor

Transmission speed sensors in your vehicle are mainly used for the calculation of actual gear ratio of the transmission when it is in use. There are typically two speed sensors in a transmission, commonly known as input shaft speed (ISS) sensor and output shaft speed (OSS) sensor. Both of these speed sensors work in conjunction to offer accurate transmission data to the powertrain control module of your vehicle.

As the name indicates, input shaft speed (ISS) sensor is used for monitoring the speed of the input shafts of the transmission, whereas the output shaft speed (OSS) sensor is used to monitor the speed of the transmissions’ output shafts. Regardless, if any one of these sensors experiences electrical issues or fall out of alignment, then it will affect the operation of the whole transmission.

Both of the sensors send data to the powertrain control module (PCM) of your vehicle after registering data. The PCM analyzes the data and determines which gear the transmission must engage for efficient driving. During this process, the desired gear ratio is compared to the actual gear ratio too, and if they do not match, then the PCM will set up a diagnostic trouble code and light up the “check engine” light on your vehicle dashboard.

You will be able to notice any of the following issues if either the ISS or OSS or both the speed sensors fail.

Harsh or Improper Shifting

The PCM will fail to accurately control the gear shifting within the transmission if it does not receive a valid signal from the speed sensors. This might cause the transmission of your vehicle to shift gears more quickly or roughly. In most cases, an issue with any one of the speed sensors will also affect the shift timing.

Cruise Control Does not Work

As the speed sensors in the transmission monitor the output and input shaft speed, it plays a crucial role in monitoring the cruise control of your vehicle. The PCM will send an error code to the ECU of your vehicle when the sensors fail to send accurate data to the unit. As a safety measure, the ECU will shut down cruise control.

If The Check Engine Light is On

When the safety sensors are not delivering accurate data to the PCM, then it will urge the PCM to set up a diagnostic trouble code. In addition to that, the PCM will also turn on the “check engine” light on your vehicle dashboard. It would be better to look for remanufactured transmissions if you are having any of these troubles.