B1021

Circuit Description
When you first turn the ignition switch to the RUN position, the Inflatable Restraint Sensing and Diagnostic Module (SDM) performs tests to diagnose critical malfunctions within itself. Next the SDM measures IGNITION 1 and the deployment loop voltages to make sure they are within their respective normal voltage ranges. Then the SDM proceeds with the RESISTANCE MEASUREMENT test. During one portion of the RESISTANCE MEASUREMENT test, the SDM does the following:
^ Grounds the DRIVER SIDE LOW terminal 3 through an internal current sink.
^ Connects the DRIVER SIDE 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 SIDE HIGH and DRIVER SIDE 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:

- Inflatable Restraint Steering Wheel Module.
- Inflatable Restraint Steering Wheel Module Coil.
- Harness wiring of circuit 347.
- Harness wiring of circuit 348.
- Connector terminal contact.

The RESISTANCE MEASUREMENT test checks for this malfunction. This test only occurs once each ignition cycle when IGNITION 1 is within the normal operating voltage range.

Action Taken When the DTC Sets
^ The SDM sets a DTC B1021.
^ The SDM turns ON the AIR BAG warning lamp.

Conditions for Clearing the 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 CODES command.
- Once 250 malfunction free ignition cycles have occurred.
When you issue a scan tool CLEAR CODES command and the malfunction is still present, the DTC will not reappear until the next ignition cycle.

Diagnostic Aids
A poor connection can cause an intermittent condition. Check the following for a poor connection:
^ The Inflatable Restraint Steering Wheel Module steering column connector terminal A and terminal B.
^ The upper Inflatable Restraint Steering Wheel Module Coil connector terminal A and terminal B.
^ The SDM wiring harness connector terminal 2 and terminal 3.
^ The wire to terminal connections in circuit 347.
^ The wire to terminal connections in circuit 348.

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

When measurements are requested in this table, use the J 39200 DMM with the correct terminal adapter from the J 35616-A Connector Test Adapter Kit. When an inspection for proper connection is requested, refer to Diagrams / Testing for Electrical Intermittents. When a wire, connector or terminal repair is requested, use the J 38125-B Terminal Repair Kit.

Test Description
The numbers below refer to the step numbers on the diagnostic table:
2. This step checks the driver deployment loop resistance that was measured by the Inflatable Restraint Sensing and Diagnostic Module (SDM).
3. This step checks to see if the Inflatable Restraint Steering Wheel Module yellow 2-way connector is corroded or damaged.
10. This step isolates the malfunction to one side of the Inflatable Restraint Steering Wheel Module yellow 2-way connector.
11. This step determines if there is a malfunctioning Inflatable Restraint Steering Wheel Module Coil or if there is a malfunctioning Inflatable Restraint Steering Wheel Module.
14. This step checks the SDM wiring harness connector for corrosion or damaged terminals.
19. This step checks to see if there is a high resistance in circuit 347.
21. This step determines if there is a high resistance in circuit 348 or if there is a malfunctioning SDM.