Fault Code 51 Intermittent Short to Ground
FAULT CODE 51Diagnostic Monitor Internal Thermal Fuse - Intermittent Short to Ground
Normal Operation
The diagnostic monitor measures the voltages at the Air Bag Diagnostic Module (DM) connector pins. When certain airbag deployment wires are shorted to ground, the system may become susceptible to unwanted deployment of the airbags. the DM senses a short to ground on any of these circuits and helps prevent unwanted airbag deployment by blowing the DM thermal fuse. Blowing the fuse removes all power (battery and back-up power) from the airbag deployment circuits. While the short to ground exists, the monitor will flash fault code 13 or code 14, depending where the short appears (see code 13 and 14 for more details). If the short to ground is intermittent and temporarily corrects itself, the DM will flash code 51.
NOTE: If the short to ground returns, the higher priority codes 13 or 14 will be flashed instead of 51.
If the airbag MIL Lamp is flashing code 51 and a short to ground has not been serviced, this means that an intermittent short to ground exists in the airbag system.
NOTE: The DM should be replaced only after repairs to the intermittent short have been completed.
The diagnostic monitor contains an internal thermal fuse that is not serviceable. The thermal fuse is controlled by a computer inside the diagnostic monitor. The computer 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 jumper out the thermal fuse with a circuit breaker or any other type of fuse.
Do not install a new diagnostic monitor until the short has been located and corrected.
Code 51 After Airbag Deployment
Occasionally, immediately after an airbag deploys, the internal wiring of the airbag may become shorted to the metal housings off the airbag. This internal airbag short is detected by the diagnostic monitor as short to ground in the airbag deployment wiring. Since the diagnostic monitor is still operating immediately after most deployments, the monitor will detect the shorted wiring and will flash code 13 and blow the internal thermal fuse. After the deployment, as the airbags cool off, the internal shorted wiring may correct itself, therefore the short to ground will no longer exist and the diagnostic monitor will flash code 51. If a vehicle with a deployed airbag is flashing code 51, inspect and replace all damaged areas. If no damage is found, assume that the deployed airbag was the cause for the intermittent short and replace the diagnostic monitor when the new airbags are installed.
NOTE: Diagnostic monitors can withstand several airbag deployments and do not need to be replaced after every deployment. Only replace the diagnostic monitor if it is damaged.
Electrical Schematic-DM Internal Thermal Fuse-intermittent Short To Ground, Fig.1:
1. Instrument Panel Fuse
2. Engine Compartment Fuse
3. Safing Sensor
4. Cable Reel Cassettes
5. Driver-side Airbag
6. Passenger-side Airbag
7. RH Impact Sensor
8. LH Impact Sensor
9. Airbag MIL Lamp
10. Diagnostic Module