Transmission Range Sensor (PRND421)

Description
There are seven sets of contacts in the selector and inhibitor switch, which are operated by the selector shaft. Each set of contacts corresponds to one of the seven selector lever positions (PRND421). Only one set of contacts will supply battery voltage to the TCM and the light emitting diode (LED) module at any one time. The TCM monitors the switch outputs every 10 ms.

A pair of contacts are also provided for the crank inhibit circuit. The contacts are only closed when the selector lever is in the 'P' and 'N' positions.

There are two diagnostic checks of the transmission range sensor, a fault is detected if: -
1. The vehicle speed is greater than 6.2 mph; the throttle angle is greater than 12.5 %; the diagnostic drive cycle is active and no signal has been received from the transmission range sensor.
2. The diagnostic drive cycle is active; the vehicle speed is greater than 6.2 mph; the throttle angle is greater than 12.5 % and the transmission range sensor has indicated multiple gear positions at the same time.

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.

Safety Warning

Transmission Position Sensor/Switch: Description and Operation

Use the Manual With the Right Hardware

When to See a Mechanic

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