Theory Of Operation

The Park/Neutral Switch rationality test is enabled only for vehicles equipped with an Automatic Transmission. This diagnostic performs a check to determine if the park/neutral switch is incorrectly stuck in the park/neutral position during driving conditions. This is done by comparing vehicle speed, engine speed, throttle position, and engine load, which can only exist if the transmission is actually in drive. The stuck in drive condition is not checked since the starter relay will not energize if the switch state indicates drive/reverse, and therefore will render the vehicle inoperable.