Malfunction Lamp / Indicator: Description and Operation

AIRBAG INDICATOR

DESCRIPTION
An airbag indicator is standard equipment on all instrument clusters. The airbag indicator is located near the left edge of the instrument cluster, next to the tachometer. The airbag indicator consists of a stencil-like cutout of the letters "SRS" in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the indicator from being clearly visible when it is not illuminated. A red Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the "SRS" text to appear in red through the translucent outer layer of the overlay when the indicator is illuminated from behind by the LED, which is soldered onto the instrument cluster electronic circuit board. The air-bag indicator is serviced as a unit with the instrument cluster.

OPERATION
The airbag (SRS) indicator gives an indication to the vehicle operator when the Airbag Control Module (ACM) has recorded a Diagnostic Trouble Code (DTC) for a Supplemental Restraint System (SRS) circuit or component malfunction. Such a DTC may indicate that the SRS is faulty or inoperative. The airbag indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and a hard wired input received by the cluster from the ACM. The airbag indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate when the instrument cluster detects that the ignition switch is in the On position. Therefore, the LED will always be off

when the ignition switch is in any position except On. The LED only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster will turn on the airbag indicator for the following reasons:

- Bulb Test - Each time the ignition switch is turned to the On position the airbag indicator is illuminated for about four seconds. The entire four second bulb test is a function of the ACM.
- Airbag Lamp-On Input - Each time the cluster receives a lamp-on input from the ACM, the airbag indicator will be illuminated. The indicator can be flashed on and off, or illuminated solid, as dictated by the ACM input. For some DTCs, if the problem does not recur, the ACM will send a lamp-off input automatically. Other DTC's may require that a fault be repaired and the ACM be reset before a lamp-off input will be sent. For more information on the ACM and the DTC set and reset parameters, The indicator remains illuminated until the cluster receives a lamp-off input from the ACM, or until the ignition switch is turned to the Off position, whichever occurs first.
- Airbag Indicator Malfunction - Following the seatbelt reminder function, each time the cluster detects a malfunction in the airbag (SRS) indicator or the airbag indicator circuit, the cluster will flash the seatbelt indicator on and off. The cluster will continue to flash the seatbelt indicator until the airbag indicator circuit fault is resolved, or until the ignition switch is turned to the Off position, whichever occurs first.

The ACM continually monitors the SRS circuits and sensors to decide whether the system is in good operating condition. The ACM then provides the proper lamp-on or lamp-off inputs to the instrument cluster. If the ACM provides a lamp-on input after the bulb test, it indicates that the ACM has detected a system malfunction and/or that the airbags and seat belt tensioners may not deploy when required, or may deploy when not required. The ACM will store a DTC for any malfunction it detects. The ACM input circuit to the instrument cluster can be diagnosed using conventional diagnostic tools and methods. For proper diagnosis of the SRS, the ACM, or the instrument cluster circuitry that controls the air-bag indicator, a diagnostic scan tool is required. Refer to the appropriate diagnostic information.