Airbag DM Fault Code 51

Airbag DM Fault Code 51

Airbag diagnostic module - thermal fuse blown.

WARNING: The diagnostic module will blow the internal fuse whenever a short circuit to ground occurs in the deployment circuits. It does not blow because of excessive current flow. The thermal fuse is not a serviceable item. No attempt should be made to replace or bypass the fuse.

WARNING: Do not install a new diagnostic module until the short has been located and corrected. A short which goes away before corrective action has been taken must be regarded as an intermittent fault. Installing a new diagnostic module when there is an intermittent fault will result in repeated diagnostic module failures and repeated repairs.

Normal Operation

In order to prevent airbag deployment in the event of a short circuit to ground, the diagnostic module blows its internal fuse as soon as a short to ground is detected. This action removes all battery and back-up power from the deployment circuits. The diagnostic module will flag the higher priority codes 13 or 14 while the short to ground exists. If the short is intermittent and temporarily corrects itself, the diagnostic module will flag code 51. If the short to ground returns, the diagnostic module will again flag the higher priority code 13 or 14 instead of code 51.

Code 51 after Airbag Deployment

The internal wiring may be shorted to the metal airbag housings after the airbags are deployed. The diagnostic module will see this as a short to ground in the deployment wiring. It will flag a code 14 and blow the internal fuse. As the deployed airbags cool, the short circuit may rectify itself. The diagnostic module will then flag a code 51. This intermittent fault must be investigated and corrected.

Possible Causes

A short circuit to ground in any of the following:

• DM pins 2-2, 2-5 or 2-6 to the safing sensor
• DM pins 2-2, 2-5 or 2-3 to the passenger airbag
• DM pins 2-2, 2-4 or 2-5 to the drivers airbag
• DM pins 1-2 or 1-11 to RH crash sensor
• DM pins 1-6 or 1-12 to LH crash sensor

Fault Analysis

1. Disarm the airbag system and fit airbag simulators (6.4.21.4).
2. Inspect the connectors and terminals for any foreign metal objects or damaged terminals which could be the cause of the short circuit.
   Check each of the circuits in the possible causes list and isolate the intermittent short circuit. Rectify the fault.
   See the warnings above about replacement of diagnostic modules when intermittent shorts are present.
3. Replace the diagnostic module.
4. Reconnect all components and rearm the airbags (6.4.21.4).