Test Notes

Diagnostic Monitor Internal Thermal Fuse--Fuse Blown Due to Intermittent Short to Ground

Short to Ground Was Serviced or Is Intermittent

Code 51 Sequence Of Events:

Normal Operation
NOTE: The air bag diagnostic monitor contains an internal thermal fuse that is not serviceable. The thermal fuse is controlled by the air bag diagnostic monitor. The air bag diagnostic monitor will blow its 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 air bag 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 air bag diagnostic monitor with an intermittent short in the system will result in repeat blown air bag diagnostic monitor thermal fuse 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 bags. 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 diagnostic trouble code 13. If the short to ground is intermittent and temporarily corrects itself, the air bag diagnostic monitor will flash diagnostic trouble code 51.

NOTE: If the short to ground returns, the higher priority diagnostic trouble code 13 will flash instead of 51.

If the air bag warning indicator is flashing diagnostic trouble code 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 to 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) you are working on. OASIS is updated daily using concern descriptions from engineering and Dealership Service sources.

2. Inspect wiring and harnesses in areas where they pass through or are located next to metal components (i.e. engine compartment bulkhead, body sheet metal, component mounting brackets, etc).

Code 51 After Air Bag Deployment

NOTE: The air bag diagnostic monitor can withstand several air bag deployments and does 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 bags may become shorted to the metal housings of the air bags. 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 diagnostic trouble code 13 and blow the internal thermal fuse. After the deployment, as the air bags cool off, the internal shorted wiring may correct itself; then the short to ground will no longer exist and the air bag diagnostic monitor will flash diagnostic trouble code 51. If a vehicle with a deployed air bag is flashing diagnostic trouble code 51, inspect and replace all the damaged areas of the vehicle with 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 bags are installed.

After a short to ground has been corrected, the air bag diagnostic monitor will flash out diagnostic trouble code 51. Diagnostic trouble code 51 indicates that the 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, then replace the 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 servicing.