Air Bag Control Module: Description and Operation

PURPOSE
Performing system diagnostics is the main purpose of the Air Bag Electronic Crash Sensor (ECS) module.

The ECS module continually monitors all air bag system components and wiring connections for possible faults when the ignition switch is in RUN position.

OPERATION
The air bag ECS module performs the following functions:
- deploys the air bags and seat belt pretensioners in the event of a deployable crash.
- monitors the air bag Safety Restraint System (SRS) for faults.
- Illuminates the air bag indicator if a fault is detected.

- Flashes the air bag indicator to indicate the Diagnostic Trouble Code (DTC) detected.
- communicates through the Data Link Connector (DLC) the current and historical DTCs.
- Activates a chime or buzzer if the air bag indicator is not available.

The ECS, together with the primary crash sensor, determines when to deploy the air bags and belt and buckle assembly pretensioners.

The ECS monitors the SRS for possible faults. If a fault is detected while the ignition switch is in the RUN position, the ECS will illuminate the air bag indicator located in the instrument cluster. When the ignition is cycled (turned Off then turned On), the air bag indicator will flash the two-digit Lamp Fault Code (LFC). The air bag indicator will flash the LFC twice, then it will remain illuminated for the rest of the key cycle. The ECS will also communicate the current and historical DTCs through the Data Link Connector (DLC), using the New Generation STAR (NGS) tester. If the air bag indicator does not function, and the system detects a fault condition, the ECS will activate an audible chime or buzzer. The chime is a series of five sets of five beeps. The buzzer is a five-seconds-on, five-seconds-off buzzing noise. If the chime or buzzer is heard, the SRS or the air bag indicator requires service.

Diagnostic trouble codes are prioritized. If two or more faults occur at the same time, the fault having the highest priority will be displayed first. After that fault has been corrected, the next highest priority fault will be displayed.

The air bag ECS includes an internal backup power supply. This feature provides sufficient backup power to deploy the air bag in the event the battery or battery cables are damaged in a collision before the safing and primary crash sensors close. The backup power supply will deplete its stored energy approximately 1 minute after the battery ground cable is disconnected.

APPLICATION NOTE:
There are three types of air bag ECS modules: a two-ignitor system for a school bus, a three-ignitor system for a cargo van and a four-ignitor system for a passenger van. These ECS modules have unique part numbers and are not interchangeable.