Supplemental Inflatable Restraint (SIR)

When measurements are requested in this chart, use SA 91114NE DVM with correct terminal adapter from SA 9206Z. When a check for proper connection is requested, refer to "Intermittents and Poor Connections." When a wire connector or terminal repair is requested, use the proper repair parts and refer to "Wiring Repair."

CAUTION: BE CAREFUL WHEN YOU HANDLE A SENSING AND DIAGNOSTIC MODULE (SDM). DO NOT STRIKE OR JOLT THE SDM. BEFORE APPLYING POWER TO THE SDM:
- REMOVE ANY DIRT GREASE, ETC. FROM THE MOUNTING SURFACE.
- POSITION THE SDM HORIZONTALLY ON THE MOUNTING SURFACE.
- POINT THE ARROW ON THE SDM TOWARD THE FRONT OF THE VEHICLE.
- TIGHTEN ALL OF THE SDM FASTENERS AND SDM BRACKET FASTENERS TO THE SPECIFIED TORQUE VALUE.
FAILURE TO FOLLOW THE CORRECT PROCEDURES COULD CAUSE AIR BAG DEPLOYMENT PERSONAL INJURY OR UNNECESSARY SIR SYSTEM REPAIRS.

CAUTION: BEFORE PERFORMING DIAGNOSTICS, THE IGNITION SWITCH MUST BE IN THE "OFF" POSITION FOR 10 MINUTES (REFER TO DISABLING AND ENABLING PRECAUTIONS).

NOTICE: When DTC 18 has been set, it is necessary to replace the SDM. Setting DTC 18 will also cause DTC 71 to set. When a Scan tool "Clear Codes" command is issued and the malfunction is still present, diagnostic trouble codes 18 and 71 will remain current. Ensure that the short to ground is repaired prior to installing a replacement Sensing and Diagnostic Module (SDM) to avoid damaging the SDM.

NOTICE: Perform "SIR DIAGNOSTIC SYSTEM CHECK" before proceeding with this chart. SIR Diagnostic System Check

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," VLR, and deployment loop voltages are measured to ensure they are within their respective normal voltage ranges. The SDM monitors the voltage at "Driver Side LO terminal A2 and "Passenger Side LO" terminal A4 to detect shorts in ground in the passenger inflator module circuits.

DTC WILL SET WHEN:
The VLR power supply in the SDM is in its normal operating voltage range and at least one of the two inflator modules is not open. Then, if the voltage measured at "Driver Side LO" is greater than three volts, and the voltage measured at "Passenger Side LO" is less than or equal to three volts for 500 milliseconds during "Continuous Monitoring" or "Current Source Diagnostic," DTC 18 will set.

ACTION TAKEN:
SDM turns On the AIR BAG telltale lamp and sets DTC 18 and also DTC 71. DTC 18 will take precedence over DTCs 15, 16, 21 and 22.

DTC WILL CLEAR WHEN:
The fault condition is removed and the SDM is replaced. DTC 18 will remain current, regardless if the ignition switch is turned Off or a Scan tool "Clear Codes" command is issued, until the faulty wiring or component is repaired or replaced and the SDM is replaced.

DTC CHART TEST DESCRIPTION:
Number(s) below refer to step number(s) on the diagnostic chart.
Step 1. This test determines whether the malfunction is occurring in the passenger inflator module, or the circuitry.
Step 2. This test checks for a short from "Passenger Side LO" to ground.
Step 3. This test checks for a short from "Passenger Side HI" to ground, or a SDM integrity problem.

DIAGNOSTIC AIDS:
It is critical to diagnose all circuitry before replacing the SDM. If the malfunction still exists, the new SDM will be damaged. An intermittent condition is likely to be caused by a short to ground in the passenger inflator module circuits. Inspect circuits 1403 and 1404 carefully for cutting or chafing. If the wiring pigtail of the passenger inflator module is damaged, the module must be replaced. If no circuit or component failures are located, after a complete and thorough inspection, the fault may have occurred internally to the SDM.

The test for this diagnostic trouble code is run during "Continuous Monitoring" and "Current Source Diagnostics," unless DTC 17 or 26 is detected.