Supplemental Inflatable Restraint (SIR)

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

When the ignition switch is turned "ON," the SDM will perform tests to diagnose critical malfunctions within itself. Upon passing these tests, "Ignition 1" 36 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 Low" terminal "A2" is grounded through a resistor and the driver current source connected to "Driver Side High" terminal "A1" allows a known amount of current to flow. After "Current Source Diagnostics" are completed the SDM removes the low resistance ground from "Driver Side Low" and switches the driver current source at "Driver Side High." The SDM then measures the voltage at Driver Side High" and "Driver Side Low" during "Continuous Monitoring." By monitoring the voltage difference between "Driver Side High" and "Driver Side Low" the SDM calculates the combined resistance of the driver inflator module, harness wiring CKTs 347 and 348 and connector terminal contact.

DTC WILL SET WHEN

The voltage difference between "Driver Side High" terminal "A1" and "Driver Side Low" terminal "A2" is above or equal to a specified value for 500 milliseconds during "Current Source Diagnostics" or "Continuous Monitoring."

ACTION TAKEN

SDM turns "ON" the "AIR BAG" warning lamp and sets a diagnostic trouble code.

DTC WILL CLEAR WHEN

The voltage difference between "Driver Side High" terminal "A1" and "Driver Side Low" terminal "A2" is below a specified value for 500 milliseconds during "Continuous Monitoring."

DTC CHART TEST DESCRIPTION

Numbers below refer to circled numbers on the diagnostic chart.

1. This test determines whether the malfunction is in the driver inflator module circuitry or in the SDM wiring harness circuitry.

2. This test checks whether the malfunction is due to high resistance in CKT 347.

3. This test checks whether the malfunction is due to high resistance in CKT 348.

4. This test determines whether the malfunction is in the driver inflator module or the SIR coil assembly.

DIAGNOSTIC AIDS

An intermittent condition is likely to be caused by a poor connection at the driver inflator module harness connector terminals "A" or "B," SDM terminals "A1" or "A2," or an open in CKT 347 or CKT 348. An intermittent open in the SIR coil assembly could also set this DTC. To test for a bad SIR coil assembly, clear DTCs, then turn the steering wheel back and forth with the ignition switch "ON." If the "AIR BAG" warning lamp comes "ON" and DTC 26 has set again, it is likely the SIR coil is malfunctioning.