Gear selector position sensor (PRNDL)
Purpose
*Detects the position of the gear selector and transmits this information to the electronic transmission control module (TCM) or engine control module (ECM).
* The TCM or ECM uses this information to control gear shifting, torque converter lock-up, reverse lamp activation, and other gear position-related functions.
Design and operating principle
A PRNDL sensor is typically an electromechanical device consisting of:
*Switch: A mechanical switch that is activated by the gear selector lever.
*Position Sensor: A sensor that converts the mechanical movement of the switch into an electrical signal.
* Electrical Contacts: Contacts that transmit the electrical signal to the TCM or ECM.
When you shift the gear selector lever, the switch moves, activating the corresponding electrical contact. The contact closes, sending an electrical signal to the TCM or ECM that corresponds to the gear position (eg P, R, N, D, L).
Types of PRNDL sensors
* Mechanical: The switch directly activates the electrical contacts.
* Electronic: A position sensor, such as a Hall effect sensor or magnetoresistive sensor, converts mechanical motion into an electrical signal.
* Non-contact: Uses inductive or capacitive sensors to detect gear selector position without physical contact.
Malfunctions and diagnostics
A malfunction of the PRNDL sensor can result in:
* Inability to shift between gears
*Check Engine light comes on
* Reverse lamps not turning on
To diagnose PRNDL sensor problems, you must use a trouble code (DTC) scanner that can read codes related to the PRNDL sensor, such as:
* P0705 – Shift Position Sensor Circuit Malfunction
* P0706 – Shift Position Sensor Input Low
* P0708 – Shift Position Sensor Input High
Maintenance and repair
In most cases, a faulty PRNDL sensor will need to be replaced. It is recommended that you take it to a qualified mechanic as replacing the sensor may require removing the transmission or other components.