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.
Automatic Transmission Input Speed Sensor
The automatic transmission input speed sensor (ISS) is a magnetic inductive pickup that relays turbine shaft speed information to the PCM/TCM. The PCM/TCM uses ISS information in order to control line pressure, transmission shift patterns and TCC apply and release. This information is also used in order to calculate the appropriate operating gear ratios and TCC slippage.
The ISS mounts in the case cover, next to the automatic transmission input speed sensor reluctor wheel assembly. An air gap of 0.08-2.12 mm (0.0032-0.0834 in) occurs between the sensor and the teeth on the speed sensor reluctor wheel as the drive sprocket rotates. The speed sensor reluctor wheel is secured to and turns with the drive sprocket by the tangs on the drive sprocket forward thrust washer.
The sensor consists of a permanent magnet surrounded by a coil of wire. As the turbine shaft rotates the speed sensor reluctor wheel and the drive sprocket, an AC signal is produced by the ISS. This AC signal consists of a voltage and frequency that changes based on vehicle speed. The PCM/TCM uses the frequency portion of this signal to determine input shaft speed. Higher input shaft speeds induce a higher frequency and a higher voltage measurement at the sensor. The voltage portion of the signal is used in diagnostic procedures.
Sensor resistance should measure between 820-1020 ohms at 20°C (68°F). Output voltage will vary with the vehicle speed from a minimum of 0.5 volts AC at 300 RPM to 200 volts at 6,000 RPM.
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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.