Air Bag Systems

Circuit Description
When the ignition switch is turned to the ON position, the Inflatable Restraint Sensing and Diagnostic and Seat Belt Pretensioner Module (SDM) performs tests to diagnose critical malfunctions within itself. The SDM monitors the six deployment loops to detect leakage currents to ground and to B+ in the Frontal Air Bag deployment loops, the Side Air Bag deployment loops and the Seat Belt Pretensioner deployment loops. Then, the deployment loop resistances are measured to ensure they are within their respective normal resistance ranges. During one portion of the RESISTANCE MEASUREMENT test, the SDM does the following:
^ Measures the voltage difference between the PASSENGER BELT HIGH and the PASSENGER BELT LOW.
^ Uses the measured voltage to calculate the resistance of the Passenger Seat Belt Pretensioner deployment loop.

Upon passing these tests, the energy reserve is charged and the firing transistors are tested. The SDM then goes into CONTINUOUS MONITORING mode. The SDM service wait time is 1 minute. Refer to ENABLE/DISABLE procedures.

Conditions for Setting the DTC
The Passenger Seat Belt Pretensioner deployment loop resistance is less than 1.6 ohms. The Passenger Seat Belt Pretensioner deployment loop consists of the following components:
^ passenger seat belt pretensioner.
^ Harness wiring of CKT AB950 and CKT AB900.
^ Harness wiring of CKT XB950 and CKT XB901.
^ Connector terminal contact.

The RESISTANCE MEASUREMENT test checks for this malfunction. This test only occurs once each ignition cycle when the IGNITION is within the normal operating voltage range.

Action Taken When the DTC Sets
^ The SDM sets a DTC 38.
^ The SDM turns ON the AIR BAG warning lamp.

Conditions for Clearing the DTC
The resistance of the Passenger Seat Belt Pretensioner deployment loop is more than 1.6 ohms. You must issue a scan tool Clear Codes command to clear a Current or History DTC.

Diagnostic Aids
A short between CKT AB950 or CKT AB900 and CKT XB950 or CKT XB901 can cause an intermittent condition. Check CKT AB950, CKT AB900, CKT XB950, and CKT XB901 carefully for cutting and/or chafing. The diagnostic table directs the technician to note the entry value of the RH PRETENS RESIST. Comparing the value of the RH PRETENS RESIST. over multiple ignition cycles can be helpful in determining if an intermittent condition exists.

Test Description
The numbers below refer to step numbers on the diagnostic table.
3. This step checks to see if the Passenger Seat Belt Pretensioner is defective.
5. This step checks terminal 45 and terminal 15 of the SDM wiring harness connector for damaged terminals or corrosion.
10. This step determines if there is a short between CKT AB950 or CKT AB900 and CKT XB950 or CKT XB901 or if there is a malfunctioning SDM.