Supplemental Inflatable Restraint (SIR)

CIRCUIT DESCRIPTION
If there is an open in the SIR coil, inflator module or wiring in the steering column the resistance between the "Sense High" input, Terminal "A7," and the "Sense Low" input, Terminal "A6," increases. This increased resistance causes a larger voltage drop from the "Sense High" input to the "Sense Low" input, across the 430 ohm resistor in the resistor module. The increase in the voltage difference between the "Sense High" input and the "Sense Low" input is noted by the DERM during the "Continuous Monitoring" tests and Code 26 is set.

TEST CONDITIONS
Test every 100 milliseconds during "Continuous Monitoring."

FAILURE CONDITIONS
Code 26 will set if the voltage at the "Sense High" input, Terminal "A7," minus the voltage at the "Sense Low" input, Terminal "A6," is greater than a certain voltage for 500 milliseconds.

ACTION TAKEN
DERM turns "On" the "Air Bag" telltale lamp.

CONDITIONS TO CLEAR
Cycle Code 26 will clear if the voltage at the "Sense High" input, Terminal "A7," minus the voltage at the "Sense Low" input, Terminal "A6," is greater than 0 volts but less than a certain voltage for 500 milliseconds after Code 26 has been set.

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 or in the diagnostic circuitry.
2. This test checks for a short from the "36 VLR" circuit to the "Sense High" circuit.
3. This test determines whether the steering column fault is due to the SIR coil or the inflator module.