VehiCROSS 4WD V6-3.5L (1999)
Sensing And Diagnostic Module: Description and Operation
SDM (Sensing and Diagnostic Module)
WARNING! DURING SERVICE PROCEDURES, BE VERY CAREFUL WHEN HANDLING A SDM. NEVER STRIKE OR JAR THE
SDM. NEVER POWER UP THE SRS WHEN THE SDM IS NOT RIGIDLY ATTACHED TO THE VEHICLE. ALL SDM AND
MOUNTING BRACKET FASTENERS MUST BE CAREFULLY TORQUED AND THE ARROW MUST BE POINTED TOWARD THE
FRONT OF THE VEHICLE TO ENSURE PROPER OPERATION OF THE SRS. THE SDM COULD BE ACTIVATED WHEN
POWERED WHILE NOT RIGIDLY ATTACHED TO THE VEHICLE WHICH COULD CAUSE DEPLOYMENT AND RESULT IN
PERSONAL INJURY.
The SDM is designed to perform the following functions in the Supplemental Restraint System (SRS):
1. Energy Reserve - The SDM maintains 24-Volt Loop Reserve (24VLR) energy supply to provide deployment energy when ignition voltage is
lost in a frontal crash.
2. Frontal Crash Detection - The SDM monitors vehicle velocity changes to detect frontal crashes which are severe enough to warrant
deployment.
3. Air Bag Deployment - When a frontal crash of sufficient force is detected, the SDM will cause enough current to flow through the air bag
assembly to deploy the air bag.
4. Malfunction Detection - The SDM performs diagnostic monitoring of SRS electrical components and sets a diagnostic trouble code when a
malfunction is detected.
5. Frontal Crash Recording - The SDM records information regarding SRS status during frontal crash.
6. Malfunction Diagnosis - The SDM displays SRS diagnostic trouble codes and system status information through the use of a scan tool.
7. Driver Notification - The SDM warns the vehicle driver of SRS malfunctions by controlling the "Air Bag" warning lamp.
The SDM is connected to the SRS wiring harness by a 24-pin connector. This harness connector uses a shorting clip across certain terminals in the
contact area. This shorting clip connects the "AIR BAG" warning lamp to ground when the SDM harness connector is disconnected or Connector
Position Assurance (CPA) is not inserted even if completely connected. This will cause the "AIR BAG" warning lamp to come "ON" steady
whenever the ignition switch is at the ON or START positions with the SDM disconnected.
