Shift Interlock: Description and Operation
Shift lock and ignition switch interlockShift lock
Cars in certain markets are equipped with an electrically operated shift lock function. This is to prevent the gear selector from being inadvertently moved from the P position. This locks the gear selector interlock pin (1) in the interlock section, locking the selector lever in the P position. Figure A.
The ignition must be switched on and the brake pedal depressed before the gear selector can be moved from the P position. (The stop (brake) light is actuated.)
When the ignition is switched on and the brake pedal is depressed, a solenoid (2) is activated in the gear selector assembly. The solenoid armature (3) is pushed in and the gear selector lock button can be pressed down as usual to select another gear. See figure B.
Shift lock is supplemented with another safety function, the ignition switch interlock. This is connected to the ignition switch by a cable. The ignition switch interlock is controlled by the gear selector position and the position of the lock cylinder (4) in the ignition switch. This means that the gear selector has to be in the P position before the ignition key can be removed from the ignition. The ignition switch interlock function is only available in combination with the shift lock. See figures A and B.
Shift lock override
To permit the gear selector to be moved from the P- position when there is no battery voltage, or if there is a fault in the shift lock mechanism, the interlock mechanism can be disconnected mechanically. The mechanical release consists of a button (5) on the gear selector assembly marked SHIFT-LOCK OVERRIDE. The ignition key must be in position I or II. When the button (5) is pressed, the solenoid lock pin (3) is released. The gear selector can now be moved from the P position if the gear selector lock button is pressed. See figure C.
While the fault remains, the mechanical release must be used together with the ignition key every time the gear selector is moved from the P position.
There is a microswitch (6) in the electrical circuit between the stop (brake) light switch and the solenoid. The microswitch only closes the circuit in the P position. This is so that the solenoid is not activated every time the driver presses the brake pedal when driving.