Supplemental Inflatable Restraint (SIR)

When measurements are requested in this chart, use SA 91114NE DVM with correct terminal adapter from SA 92O6Z. When a check for proper connection is requested, refer to "Intermittents and Poor Connections." When a wire connector or terminal repair is requested, use the proper repair parts and refer to "Wiring Repair."

CAUTION: BEFORE PERFORMING DIAGNOSTICS, THE IGNITION SWITCH MUST BE IN THE "OFF" POSITION FOR 10 MINUTES (REFER TO DISABLING AND ENABLING PRECAUTIONS).

NOTICE: Perform "SIR DIAGNOSTIC SYSTEM CHECK" before proceeding with this chart. SIR Diagnostic System Check

CIRCUIT DESCRIPTION
When the ignition switch is turned On, the Sensing and Diagnostic Module (SDM) will perform tests to diagnose critical malfunctions within itself. Upon passing these tests "Ignition 1," VLR, and deployment loop voltages are measured to ensure they are within their respective normal voltage ranges. The SDM then proceeds with the "Current Source Diagnostics." "Driver Side LO" terminal A3 is grounded through a resistor and the driver current source connected to "Driver Side HI" terminal A2 allows a known amount of current to flow. By monitoring the voltage difference between "Driver Side HI" and "Driver Side LO" the SDM calculates the combined resistance of the driver inflator module, SIR coil assembly, harness wiring circuits 347 and 348 and connector terminal contact.

DTC WILL SET WHEN:
The combined resistance of the driver inflator module, harness wiring circuits 347 and 348 and connector terminal contact is greater than 4.5 ohms. This test is run once each ignition cycle during the "Current Source Diagnostics" when:
1. No "higher priority faults" are detected during "Turn.On,"
2. No "higher priority faults" are detected during "Continuous Monitoring,"
3. "Ignition 1" voltage is above a specified value.

ACTION TAKEN:
SDM turns On the AIR BAG telltale lamp and sets DTC 21.

DTC WILL CLEAR WHEN:
The malfunction is no longer occurring and the ignition switch is turned Off, or a Scan tool "Clear Codes" command is issued.

DTC CHART TEST DESCRIPTION:
Number(s) below refer to step number(s) on the diagnostic chart.
Step 1. This test determines whether the malfunction is in the driver inflator module circuitry or in the SDM wiring harness circuitry.
Step 2. This test checks whether the malfunction is due to high resistance in circuit 347.
Step 3. This test checks whether the malfunction is in the driver inflator module or the SIR coil assembly.
Step 4. This test checks whether the malfunction is due to high resistance in circuit 348.

DIAGNOSTIC AIDS:
An intermittent condition is likely to be caused by a poor connection at terminals A or B of the SIR coil connector at the base of the steering column, terminals A or B of the driver inflator module connector at the top of the steering column, SDM terminals A2 or A3 or a poor wire to terminal connection in circuit 347 or 348. The test for this diagnostic trouble code is only run while the AIR BAG telltale lamp is performing the bulb check, unless DTC 17 or 26 is detected. When a Scan tool "Clear Codes" command is issued and the malfunction is still present, the DTC will not reappear until the next ignition cycle.