Perimeter Anti-theft

WARNING: This page is about a different car, the 2003 Mercury Sable and 2003 Ford Taurus. However, it is still accessible from the selected car via links, so may be relevant.

The perimeter anti-theft feature provides an audible and visual alarm when unauthorized access to the vehicle is detected. When an intrusion is detected by any door or liftgate ajar switches, or the hood and trunk tamper switches it sends a ground signal to the GEM. When the GEM receives a signal indicating intrusion into the vehicle, the GEM supplies a ground signal to the horn control relay and the park lamps relay. The relay closes, supplying the power which activates the horn and the park lamps. The pulse stretcher module applies to wagons only. Due to the distance between the liftgate disarm switch and the GEM, the disarm switch signal is not present long enough for the GEM to recognize. The pulse stretcher module receives pulse input when switch is turned to unlock. The pulse stretcher module holds the pulse active for about 60ms so the GEM can recognize the signal and disarm the system. The perimeter anti-theft feature does not arm until 20 seconds elapses after locking the vehicle. The perimeter anti-theft device will disarm only when

unlock is pressed on the keyless entry remote transmitter.
keyless entry keypad code is entered.
door, luggage compartment lid or liftgate lock cylinder is turned to unlock.
ignition switch position changes to run or start.