Air Bag Control Module: Description and Operation

DESCRIPTION
The Airbag Control Module (ACM) contains the safing sensor, and a microprocessor that monitors the safing and impact sensor signals, as well as the air-bag system electrical circuits to determine the system readiness. The ACM contains On-Board Diagnostics (OBD), and will light the airbag warning lamp in the instrument cluster when a monitored airbag system fault occurs.

OPERATION
The ACM also contains an energy-storage capacitor. This capacitor stores enough electrical energy to deploy the airbag for up to one second following a battery disconnect or failure during an impact. The purpose of the capacitor is to provide airbag system protection in a severe secondary impact, if the initial impact has damaged or disconnected the battery, but was not severe enough to deploy the airbag.

CIRCUIT OPERATION
Two circuits provide battery voltage to the Airbag Control Module (ACM); F14 and F23. Circuits F14 and F23 are connected to separate bus bars in the fuse block. Different circuits from the Power Distribution Center (PDC) and the ignition switch supply battery voltage to the fuse block bus bars.

Circuit F23 supplies battery voltage to the ACM only when the ignition switch is in the RUN position. Circuit F14 powers the ACM when the ignition switch is in either the START or RUN position.

In either the START or RUN position, the ignition switch connects circuit A21 circuit with circuit A1 from fuse 3, a 40 amp, in the PDC. Circuit A21 circuit supplies battery voltage to the fuse block bus bar that feeds circuit F14. Fuse 12, a 15 amp, in the fuse block protects circuit F14. Circuit F14 connects to cavity 6 of the ACM.

When the ignition switch is in the RUN position, it connects circuit A2 from fuse 2, a 40 amp, in the PDC to circuit A22. Circuit A22 supplies battery voltage to the fuse block bus bar that feeds circuit F23. Fuse 16, a 15 amp, in the fuse block protects circuit F23. Circuit F23 connects to cavity 5 of the ACM.

The ACM is case grounded and has an external dedicated ground, circuit Z6.