Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Speed Sensor, Output Shaft
The speed sensor for the output shaft is located inside the gearbox. The sensor provides a signal to the transmission control module (TCM) on vehicle speed. The sensor is a so-called "active sensor" (Hall sensor) and is supplied with 12 V power. When the pulse wheel rotates (the wheel for shift-lock), the sensor generates a pulsed current (square wave), where the strength of the current depends on the position of the pulse wheel. The signals from the coil in the sensor are then acted on by magnetic-sensitive resistance, which means that the output signal is a current which fluctuates between 7 mA and 14 mA, and whose frequency increases with speed. The transmission control module (TCM) uses information on output shaft speed for:
- calculating how much torque reduction shall be requested from the engine control module (ECM) with gearshifting
- comparing engine speed with output shaft speed to calculate the slipping speed of the torque converter
- calculating gearshift timing
- calculating engagement and disengagement of the lock-up function
- comparing the signal with the signal from the transmission speed sensor for the input shaft, for calculating the current gear ratio. This is performed to identify whether the value corresponds with the expected gear ratio.
The speed sensor for the output shaft can be diagnosed.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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