Supplemental Inflatable Restraint (SIR)

CIRCUIT DESCRIPTION
The DERM injects a current through the steering column from the "Force High" output, terminal "A4," to the "Force Low" output, terminal "A10." By monitoring the difference between the voltage at the "Sense High" input, terminal "A7," and the "Sense Low" input, terminal "A6," the DERM calculates the combined resistance of the inflator module, SIR coil assembly, deployment loop and connector terminal contact in the steering column.

TEST CONDITIONS
Tested once each ignition cycle during the "Steering Column Resistance Test" if: 1) No faults are detected during the "Turn-ON Tests"; 2) No faults are detected during the "Continuous Monitoring Tests" for one second; 3) No "Crank" signal present; 4) "Ignition 1" voltage is present.

FAILURE CONDITIONS
DTC 21 will set if the combined resistance of the inflator module, SIR coil assembly, harness wiring and connector terminal contact in the steering column is greater than a specified value.

ACTION TAKEN
The DERM illuminates the "INFL REST" indicator.

CONDITIONS TO CLEAR
Current DTC 21 will be cleared each time the ignition switch is turned to "OFF."

TEST DESCRIPTION:
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This test determines whether the fault is in the steering column circuitry or the diagnostic circuitry.
2. This test checks the integrity of the 430 ohm resistor and associated circuitry in the resistor module.
3. This test determines whether the steering column fault is due to the SIR coil assembly or to the inflator module.
4. This test checks the integrity of the 100 ohm resistor and associated circuitry in the resistor module.
5. This test checks the integrity of the "Sense Low" 2490 ohm resistor and associated circuitry in the resistor module.
6. This test checks for a short from the "Force High" CKT 714 to the "Sense High" CKT "53.
7. This test determines whether the fault is due to a short to B+ in the "Sense High" CKT 753 or a faulty DERM.