B1021

Circuit Description
When you first turn the ignition switch to the RUN position, the Inflatable Restraint Sensing and Diagnostic Module (SDM) performs tests in order to diagnose critical malfunctions within itself. Then the SDM measures Ignition Positive Voltage and the deployment loop voltages in order to ensure they are within the normal voltage ranges. Then the SDM proceeds with the Resistance Measurement test. During one portion of the Resistance Measurement test, the SDM performs the following actions:
^ Grounds the Driver Low terminal 3 through an internal current sink
^ Connects the Driver High terminal 2 to an internal constant current source. This current produces proportional voltage drops in the deployment loop
^ Measures the voltage difference between Driver High and Driver Low
^ Calculates the resistance of the driver deployment loop using the measured voltage

Conditions for Setting the DTC
^ The driver and passenger deployment loops are not open.
^ The driver and passenger deployment loops are not shorted to voltage.
^ The driver deployment loop is not shorted to ground.
^ The driver deployment loop resistance is more than 3.8 ohms. The driver deployment loop consists of the following components:
- An Inflatable Restraint Steering Wheel Module
- An Inflatable Restraint Steering Wheel Module Coil
- Harness wiring of circuit 347 (WHT)
- Harness wiring of circuit 348 (DK GRN)
- Connector terminal contact

The Resistance Measurement test checks for this malfunction. This test only occurs once each ignition cycle when Ignition Positive Voltage is within the normal operating voltage range.

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

Conditions for Clearing the MIL/DTC
The DTC will clear when one of the following conditions is met:
^ Current DTC
The resistance of the driver deployment loop is less than 3.8 ohms and the ignition switch is cycled.
^ History DTC
- You issue a scan tool Clear DTCs command.
- 250 ignition cycles have passed since the last malfunction.
When you issue a scan tool Clear DTCs command and the malfunction is still present, the DTC will not reappear until the next ignition cycle.

Diagnostic Aids
A poor connection may cause an intermittent condition. Inspect the following items for a poor connection:
^ The Inflatable Restraint Steering Wheel Module steering column connector terminals A and B
^ The upper Inflatable Restraint Steering Wheel Module Coil connector terminals A and B
^ The SDM terminals 2 and 3
^ The wire to terminal connections in circuit 347 (WHT)
^ The wire to terminal connections in circuit 348 (DK GRN)

The diagnostic table directs the technician to note the entry value of Driver Resistance. Comparing the value of Driver Resistance over multiple ignition cycles may be helpful in determining if an intermittent condition exists.

When measurements are requested in this table, use the J 39200 Digital Multi meter with the correct terminal adapter from the J 35616-A Connector Test Adapter Kit. When an inspection for proper connection is requested, refer to Intermittents and Poor Connections Diagnosis in Wiring Systems. When a wire, connector or terminal repair is requested, use the J 38125-B Terminal Repair Kit. Refer to Wiring Repairs in Wiring Systems.

Test Description
The numbers below refer to the step numbers on the diagnostic table:
2. This test determines the deployment loop resistance measured by the Inflatable Restraint Sensing and Diagnostic Module (SDM).
3. This test checks for proper contact or corrosion of the yellow 2-way connector.
10. This test isolates the malfunction to one side of the Inflatable Restraint Steering Wheel Module yellow 2-way connector.
11. This test determines whether the malfunction is due to the Inflatable Restraint Steering Wheel Module or the module coil.
14. This test checks for proper contact or corrosion of the 3DM connector.
19. This test determines whether the malfunction is in circuit 347 (WHT).
21. This test determines whether the malfunction is in circuit 348 (DK GRN).