Supplemental Inflatable Restraint (SIR)

CIRCUIT DESCRIPTION
The DERM measures the deployment loop energy reserve voltage ("36 VLR") and checks that it has reached a certain voltage within seven seconds after "IGN 1" is applied. If this voltage is not reached Code 41 is set. The DERM monitors the "36 VLR" and checks that it remains above a certain voltage while "IGN 1" voltage is present. If the "36 VLR" falls below a certain voltage after initial charging, Code 42 is set. These codes indicate a fault internal to the DERM or a short to ground or B+ between the diode attached to Terminal "B" of the arming sensor and the "36 VLR" output Terminal "A2."

TEST CONDITIONS
Code 41 is tested once each ignition cycle at "Turn-On." Code 42 is tested every 100 milliseconds during "Continuous Monitoring."

FAILURE CONDITIONS
Code 41 will set if the "36 VLR" has not reached a certain voltage seven seconds after "Turn-On." Code 42 will set if the "36 VLR" is below a certain voltage after initial charging.

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

CONDITIONS TO CLEAR
Cycle Code 41 will clear each time the ignition switch is turned "Off." Cycle Code 42 will clear if the "36 VLR" is greater than a certain voltage for 500 milliseconds after Code 42 has set.

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This test checks whether the DERM has set the code falsely.
2. This test determines whether the fault is due to a short in the arming sensor or a short from the "36 VLR" circuit to B+.