A typical vehicle has nine sensors, including the speed sensor, that communicate with the powertrain control module. This control center is how the engine understands what is occurring within the block and the accessories that make it function.
The speed sensor watches the speed of the vehicle and reports it back to the PCM. This communication helps control gear shifting, as well as any clutch locking up on the torque converter.
Since the speed sensor reports about the movement of the car, if the communication becomes garbled or missing completely, the transmission loses the ability to know where it is in its shifting pattern and fails.
If a speed sensor needs replacing, it is normally near the transaxle, the head of the speedometer, differential or transmission. Additionally, another symptom of a problematic speed sensor is losing the ability to use the cruise control setting on the vehicle.
