Supplemental Inflatable Restraint (SIR)

Electrical 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 monitors the voltages at "Driver Side Low" terminal "A2" and "Passenger Side Low" terminal "A5" to detect shorts to B+ in the inflator module circuits.

DTC WILL SET WHEN

The 36 VLR power supply in the SDM is in its normal operating voltage range and neither of the two inflator modules is open. Then the voltage measured at "Driver Side Low" and "Passenger Side Low" is within a specified range. Once these conditions are met the SDM will ground "Driver Side Low" and "Passenger Side Low" through a resistor and check that "Ignition 1" is in the normal operating voltage range. When all previous conditions are met and the voltage measured at "Driver Side Low" and at "Passenger Side Low" is above a specified value, DTC 25 will set.

ACTION TAKEN

SDM turns "ON" the "AIR BAG" warning lamp, sets DTC 25 and also DTC 71.

DTC WILL CLEAR WHEN

The malfunction is no longer occurring and the ignition switch is turned "OFF," however, DTC 71 will remain current.

DTC CHART TEST DESCRIPTION

Number(s) below refer to circled number(s) on the diagnostic chart.

1. This test determines whether the malfunction is occurring in the driver inflator module circuitry.

2. This test determines whether the malfunction is occurring in the passenger inflator module circuitry.

3. This test checks for a short from "Driver Side High" to B+.

4. this test checks for a short from "Driver Side Low" to B+.

5. This test checks for a short from "Passenger Side High" to B+.

6. This test checks for a short from "Passenger Side Low" to B+

DIAGNOSTIC AIDS

An intermittent condition is likely to be caused by a short to B+ in the inflator module circuits. A DTC 25 history would be accompanied by DTC 71 current. A careful inspection of the circuits and components indicated on DTC 25 charts is essential to ensure that the replacement SDM will not be damaged.