Air Bag Control Module: Description and Operation
AIRBAG CONTROL MODULEFig.2 Airbag System Components:
The Airbag Control Module (ACM) contains the safing sensor and energy reserve capacitor. The safing sensor is located inside the ACM. The module is mounted on the tunnel/floor pan in front of the gear shift lever and below the center of the instrument panel.
The safing sensor protects against accidental airbag deployment. The ACM monitors the system to determine the system readiness. The ACM will store sufficient energy to deploy the airbags for up to one second after the battery is disconnected. The ACM contains on-board diagnostics, and will illuminate the AIRBAG warning lamp in the cluster when a fault is detected. The warning equipment is tested for 6 - 8 seconds every time the vehicle is started.
DIAGNOSTIC TROUBLE CODES
Active Codes
An active trouble code indicates an on-going malfunction. This means the defect is there every time the ACM checks that circuit/function. It is impossible to erase an active code; active codes are automatically erased by the ACM when the reason for the code has been corrected.
Stored Codes
Airbag codes are continuously stored in the ACM's memory when the ignition is turned OFF with the exception of the Loss of Ignition Run Only code, which is an active code only.
A stored code indicates there was an active code present at some time. However, the code currently may not be present as an active code, although another active code could be.
When a trouble code occurs, the AIRBAG warning lamp illuminates for 12 seconds minimum (even if the problem existed for less than 12 seconds). The code is stored, along with the time in minutes that it was active, and the number of times the ignition has been cycled since the problem was last detected.
The minimum time shown for any code will be one minute, even if the code was actually present for less than one minute. Thus, the time shown for a code that was present for two minutes 13 seconds would be 3 minutes.
If a malfunction is detected, a diagnostic trouble code is stored and will remain stored as long as the malfunction exists. When and if the malfunction ceases to exist the code is stored and an ignition cycle count will be initiated for the code. If the ignition cycle count reaches 100 without reoccurrence of that same malfunction, that diagnostic trouble code is erased and that ignition cycle counter is reset to zero. If the malfunction reoccurs before the count reaches 100, then the ignition cycle counter will be reset and the diagnostic trouble code will continue to be a stored code.
If a malfunction is not active while performing a diagnostic test procedure, the active code diagnostic test will not locate the source of the problem. In this case, the stored code can indicate an area to inspect.
Maintain a safe distance from all airbags while performing the following inspection. If no obvious problems are found, erase the stored code, and with the ignition "ON", wiggle the wire harness and connectors, rotate the steering wheel from stop to stop. Recheck for codes periodically as you work through the system. This procedure may uncover a malfunction that is difficult to locate.