Malfunction Lamp / Indicator: Description and Operation
AIRBAG INDICATORAn airbag indicator lamp is standard equipment on all instrument clusters, but is electronically disabled on vehicles not equipped with airbags. The airbag indicator lamp is located near the lower edge of the instrument cluster overlay, to the right of the odometer/trip odometer Vacuum-Fluorescent Display (VFD). The airbag indicator lamp consists of a stenciled cutout of the word "AIRBAG" in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the indicator from being clearly visible when the lamp is not illuminated. A red lens behind the cutout in the opaque layer of the overlay causes the "AIRBAG" text to appear in red through the translucent outer layer of the overlay when it is illuminated from behind by a replaceable incandescent bulb and bulb holder unit located on the instrument cluster electronic circuit board. The airbag indicator lamp is serviced as a unit with the instrument cluster.
The airbag indicator lamp gives an indication to the vehicle operator when the airbag system is faulty or inoperative. This lamp is controlled by a transistor on the instrument cluster circuit board based upon the cluster programming and electronic messages received by the cluster from the Airbag Control Module (ACM) over the Chrysler Collision Detection (CCD) data bus. The airbag indicator lamp bulb receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output (st-run) circuit whenever the ignition switch is in the ON or Start positions; therefore, the lamp will always be OFF when the ignition switch is in any position except ON or Start. The lamp bulb only illuminates when it is switched to ground by the instrument cluster transistor. The instrument cluster will turn ON the airbag indicator lamp for the following reasons:
- Bulb Test - Each time the ignition switch is turned to the ON position the lamp is illuminated for about seven seconds.
- ACM Lamp-ON Message - Each time the cluster receives two consecutive lamp-ON messages from the ACM, the lamp will be illuminated. The lamp remains illuminated for about twelve seconds or until the cluster receives two consecutive lamp-OFF messages from the ACM, whichever is longer.
- Communication Error - If the cluster receives no airbag messages for five consecutive seconds, or if the messages received have an improper check sum, the lamp is illuminated. The lamp remains illuminated for about twelve seconds or until the cluster receives a single lamp-OFF message from the ACM, whichever is longer.
- Actuator Test - Each time the cluster is put through the actuator test, the lamp will be turned ON and OFF in a prescribed sequence to confirm the functionality of the lamp and the cluster circuitry.
The ACM continually monitors the airbag system circuits and sensors to decide whether the system is in good operating condition. The ACM then sends the proper lamp-ON or lamp-OFF messages to the instrument cluster. If the airbag indicator lamp fails to light during the bulb test, replace the bulb with a known good unit. For further diagnosis of the airbag indicator lamp or the instrument cluster circuitry that controls the lamp, (Refer to INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING). If the instrument cluster turns ON the airbag indicator lamp after the bulb test, it may indicate that a malfunction has occurred and that the airbags may not deploy when required or may deploy when not required. In addition, if the airbag indicator lamp or the transistor that energizes the lamp are inoperative, the instrument cluster will send an electronic fault message to the ACM. For proper diagnosis of the airbag system, the CCD data bus, or the message inputs to the instrument cluster that control the airbag indicator lamp, a DRB III scan tool and the appropriate diagnostic information are required.