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, harness wiring CKTs 347 and 348 and connector terminal contact in the steering column.

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

FAILURE CONDITIONS
DTC 22 will set if the combined resistance of the inflator module, SIR coil, harness wiring and connector terminal contact in the steering column is less than a specified value.

ACTION TAKEN
DERM turns "ON" the "INFL REST" warning lamp.

CONDITIONS TO CLEAR
Current DTC 22 will be cleared each time the ignition switch is turned "OFF."

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This test determines whether the malfunction is in the steering column 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 checks the integrity of the 49.9 ohm resistor, 100 ohm resistor and associated circuitry in the resistor module.
4. This test checks the integrity of the two 2490 ohm resistors and associated circuity in the resistor module.
5. This test determines whether the steering column malfunction is due to the SIR coil or the inflator module.
6. This test checks for a short from CKT 347 to CKT 348.
7. This test checks for an open in the "Sense High" circuit.
8. This test checks for a short from the "Sense High" circuit to the "Force Low" circuit.
9. This test checks for a short from the "Sense Low" circuit to the "Force High" circuit.
10. This test checks for a short from the "Sense Low" circuit to the "Sense High" circuit.