Air Bag Indicator - Operation

OPERATION

The airbag indicator gives an indication to the vehicle operator when the airbag system, or a circuit or component of the system is ineffective. The airbag indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the Occupant Restraint Controller (ORC) over the Controller Area Network (CAN) data bus.

The airbag indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit. This logic only allows the indicator to operate when the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the LED is always off when the ignition switch is in any position except ON or START. The LED only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster turns on the airbag indicator for the following reasons:

- Bulb Test - Each time the ignition switch turns to the on position the airbag indicator illuminates for about six to eight seconds. The entire bulb test is a function of the ORC.
- Airbag Indicator Lamp-On Message - Each time the cluster receives an electronic airbag indicator lamp-on message from the ORC, the airbag indicator illuminates. The indicator remains illuminated for about twelve seconds or until the cluster receives a lamp-off message from the ORC, whichever is longer. This indicator will also be extinguished when the ignition switch is turned to the off position.
- Communication Error - If the cluster receives no lamp-on or lamp-off messages from the ORC for 10 consecutive message cycles, the airbag indicator illuminates. The indicator remains illuminated until the cluster receives a single lamp-off message from the ORC.
- Self Test - Each time the cluster is put through the self test, the airbag indicator turns on, then off again during the bulb check portion of the test to confirm the functionality of the LED and the cluster control circuitry. The actuator test illumination of the airbag indicator is a function of the instrument cluster.

The ORC continually monitors the airbag system circuits and sensors to decide whether the system is in good operating condition. The ORC then sends the proper lamp-on or lamp-off message to the instrument cluster, also known as the Cab Compartment Node (CCN). If the ORC sends a lamp-on message after the bulb test, it indicates that the ORC has detected a system malfunction or that the airbags and seatbelt tensioners may not deploy when required, or may deploy when not required. The ORC stores a Diagnostic Trouble Code (DTC) for any malfunction it detects. Each time the airbag indicator fails to illuminate due to an open or short in the cluster airbag indicator circuit, the cluster sends a message notifying the ORC of the condition, the instrument cluster and the ORC each store a DTC, and the cluster flashes the seatbelt indicator on and off as a backup to notify the vehicle operator.

Use a diagnostic scan tool for proper diagnosis of the airbag system, the ORC, the CCN, the CAN data bus or the electronic communication related to airbag indicator operation. Refer to the appropriate diagnostic information.