Test Notes

Air Bag Diagnostic Monitor Internal Thermal Fuse Blown Due to Intermittent Short to Ground

Normal Operation

NOTE: The air bag diagnostic monitor contains an internal thermal fuse that is not serviceable. The thermal fuse is controlled by the microprocessor inside the air bag diagnostic monitor. The microprocessor inside the air bag diagnostic monitor will blow the thermal fuse whenever a short on the deployment circuits occurs. The thermal fuse does not blow because of excessive current flowing through it. DO NOT attempt to short circuit the thermal fuse with a circuit breaker or any other type of fuse.

WARNING: DO NOT INSTALL A NEW DIAGNOSTIC MONITOR UNTIL THE SHORT HAS BEEN LOCATED AND CORRECTED. IF A SHORT TO GROUND HAS NOT BEEN LOCATED AND CORRECTED, THEN THE SHORT TO GROUND IS INTERMITTENT AND IS NOT PRESENT AT THIS TIME. INSTALLING A NEW DIAGNOSTIC MONITOR WITH AN INTERMITTENT SHORT IN THE SYSTEM WILL RESULT IN REPEAT BLOWN DIAGNOSTIC MONITORS AND REPEAT SERVICE.

The air bag diagnostic monitor measures the voltages at the air bag diagnostic monitor connector pins. When certain air bag deployment wires are shorted to ground (heavy lines illustrated in the schematic), the system may become susceptible to unwanted deployment of the air bag(s). The air bag diagnostic monitor senses a short to ground on any of these circuits and helps prevent unwanted air bag deployment by blowing the air bag diagnostic monitor thermal fuse. Blowing this fuse removes all power (battery and backup power) from the air bag deployment circuits. While the short to ground exists, the air bag diagnostic monitor will flash DTC 13 or DTC 14, depending on where the short appears (refer to DTC 13 and 14 for more details). If the short to ground is intermittent and temporarily corrects itself, the air bag diagnostic monitor will flash DTC 51.

NOTE: If the short to ground returns, the higher priority DTCs 13 or 14 will be flashed instead of 51.

If the air bag indicator is flashing DTC 51 and a short to ground has not been serviced, this means that an intermittent short to ground exists in the air bag system. The air bag diagnostic monitor should be replaced only after service of the intermittent short has been completed.

Some service tips for finding an intermittent short to ground are:
1. Consult OASIS (Restraint Systems Service Code 104000) for up-to-date diagnostics and descriptions of wiring concern locations for the vehicle (VIN number) on which you are working. OASIS is updated daily using concern descriptions from engineering and Dealership Service sources.
2. Inspect wiring and harnesses in areas through which they pass or are located next to metal components (i.e. engine compartment bulkhead, body sheet metal, component mounting brackets, etc.).

DTC 51 After Air Bag Deployment

NOTE: Air bag diagnostic monitors can withstand several air bag deployments and do not need to be replaced after every deployment. Only replace the air bag diagnostic monitor if it is damaged.

Occasionally, after an air bag deploys, the internal wiring of the air bag(s) may become shorted to the metal housings of the air bag(s). This internal air bag short is detected by the air bag diagnostic monitor as short to ground in the air bag deployment wiring. Since the air bag diagnostic monitor is still operating immediately after most deployments, the air bag diagnostic monitor will detect the shorted wiring and will flash DTC 13 or 14 and blow the internal thermal fuse. After the deployment, as the air bag(s) cool off, the internal shorted wiring may correct itself. The short to ground will no longer exist and the air bag diagnostic monitor will flash DTC 51. If a vehicle with a deployed air bag is flashing DTC 51, inspect and replace all the damaged areas of the vehicle that have crushed wiring, sensors, etc. If no damage is found, assume that the deployed air bag was the cause for the intermittent short and replace the air bag diagnostic monitor when the new air bag(s) is installed.

After a short to ground has been corrected, the air bag diagnostic monitor will flash out DTC 51. DTC 51 indicates that the thermal fuse inside the air bag diagnostic monitor is blown and the short to ground no longer exists.

If a short to ground has not been located and serviced (short to ground corrected itself), consult OASIS for potential wiring shorts.

If a short to ground has been correctly located and serviced, replace air bag diagnostic monitor. DO NOT replace air bag diagnostic monitor until the short to ground has been positively located and serviced. Replacing air bag diagnostic monitor before servicing a short to ground will result in repeat service.