Air Bag Systems

Circuit Description
When the ignition switch is turned to the ON position, the Inflatable Restraint Sensing and Diagnostic and Seat Belt Pretensioner Module (SDM) performs tests to diagnose critical malfunctions within itself. The SDM monitors the six deployment loops to detect leakage currents to ground and to B+ in the frontal air bag deployment loops, the side air bag deployment loops and the seat belt pretensioner deployment loops. Then, the deployment loop resistances are measured to ensure they are within their respective normal resistance ranges. During one portion of the RESISTANCE MEASUREMENT test, the SDM does the following:
^ Measures the voltage difference between the DRIVER FRONTAL HIGH and the DRIVER FRONTAL LOW.
^ Uses the measured voltage to calculate the resistance of the driver frontal air bag deployment loop.

Upon passing these tests, the energy reserve is charged and the firing transistors are tested. The SDM then goes into CONTINUOUS MONITORING mode. The SDM service wait time is 1 minute. Refer to ENABLE/DISABLE procedures.

Conditions for Setting the DTC
The driver frontal air bag deployment loop resistance is more than 5.0 ohms. The driver frontal air bag deployment loop consists of the following components:
^ Inflatable Restraint Steering Wheel Module.
^ Inflatable Restraint Steering Wheel Module Coil.
^ Harness wiring of CKT BM30.
^ Harness wiring of CKT B30.
^ Harness wiring of CKT BM1.
^ Harness wiring of CKT B1.
^ Connector terminal contact.

The RESISTANCE MEASUREMENT test checks for this malfunction. This test only occurs once each ignition cycle when the IGNITION is within the normal operating voltage range.

Action Taken When the DTC Sets
^ The SDM sets a DTC 31.
^ The SDM turns ON the AIR BAG warning lamp.

Conditions for Clearing the DTC
The resistance of the Driver Frontal Air Bag deployment loop is less than 5.0 ohms. You must issue a scan tool Clear Codes command to clear a Current or History DTC.

Diagnostic Aids
A poor connection can cause an intermittent condition. Check the following for a poor connection:
^ The Inflatable Restraint Steering Wheel Module Coil integral 2-way connector terminal 1 and terminal 2.
^ The Inflatable Restraint Steering Wheel Module Coil wiring harness connector terminal 7 and terminal 8.
^ The SDM wiring harness connector terminal 1 and terminal 2.
^ The SDM terminal 1 and terminal 2.
^ The wire to terminal connections in CKT BM30.
^ The wire to terminal connections in CKT B30.

The diagnostic table directs the technician to note the entry value of the DRIVER AIR BAG RESISTANCE. Comparing the value of the DRIVER AIR BAG RESISTANCE over multiple ignition cycles can be helpful in determining if an intermittent condition exists.

Test Description
The numbers below refer to step numbers on the diagnostic table.
3. This step checks to see if the Inflatable Restraint Steering Wheel Module is defective.
5. This step checks to see if the Inflatable Restraint Steering Wheel Module Coil is defective.
12. This step checks for an open or a high resistance in CKT BM30.
14. This step determines if there is an open or a high resistance in CKT B30 or if there is a malfunctioning SDM.