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.
Transmission Input Speed Sensor (Speed Of The Input Shaft)
The transmission input speed sensor (input shaft speed) is on the upper side of the transmission housing. The sensor is an active sensor and is supplied with 12 V. When the pulse wheel on clutch C1 rotates, the sensor generates a pulsed current (quadratic 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 effected by a magnetic resistance element, which generates a current which oscillates between 7 mA and 14 mA, and the frequency of which increase with speed. The transmission control module (TCM) calculates the transmission input speed using the signal from the sensor.
The transmission control module (TCM) uses information about the input shaft speed to calculate the torque reduction to be requested from the engine control module (ECM) when shifting. The value is also used to compare the engine speed (RPM) with the speed of the input shaft in order to calculate the slipping rate of the torque converter. The value is also compared with the transmission output speed sensor signal in order to calculate the actual gear ratio. This is done to check whether the value corresponds to the expected gear ratio.
There are diagnostics for the transmission input speed sensor.
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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.