Back-Up Power Supply
WARNING: This page is about a different car, the 2002 Mercury Villager. However, it is still accessible from the selected car via links, so may be relevant.
Back-up power supply is located inside diagnostic monitor. If battery or battery cables are damaged in a collision before impact sensors close circuit, back-up power supply will deploy air bag. Back-up power supply will hold deployment charge for about 3 minutes after negative battery cable is disconnected.