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 Shaft Speed Sensor
The Automatic Transmission Input Shaft Speed Sensor (AT ISS) is a magnetic inductive pickup that relays information about the transmission input speed to the PCM. See Fig 1 or Fig 2 . The PCM uses this information to control the line pressure, TCC apply and release, and the transmission shift patterns. This information is also used to calculate the appropriate operating gear ratios and TCC slippage. The AT ISS mounts on the transmission case under the channel plate next to the drive sprocket. An air gap of 0.010-0.114" (0.26-2.90 mm) is maintained between the sensor and the teeth of the drive sprocket. The sensor consists of a permanent magnet surrounded by a coil of wire. As the drive sprocket is driven by the turbine shaft, an AC signal is induced in the AT ISS. Higher engine speeds induce a higher frequency and voltage measurement at the sensor. Sensor resistance should be 625-725 ohms when measured at 68°F (20°C). Output voltage will vary with speed from a minimum of 0.5 volts AC at 550 RPM, to 200 volts AC at 7000 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.