Diagnostic Instructions
DTC Descriptors
DTC B3855 : Rollover Sensor Performance
DTC B3856 : Discard Rollover Sensor
DTC B3857 : Incorrect Rollover Sensor Installed
Circuit/System Description
The inflatable restraint vehicle rollover sensor (ROS) utilizes battery power supply and a bidirectional interface circuit. The ROS modulates current on the interface to send ID, State of Health, and deployment commands to the inflatable restraint sensing
and diagnostic module (SDM). When the ignition is turned on the ROS responds by performing internal diagnostics and sending an ID to the SDM. The ROS continually communicates status messages to the SDM, which determines if a fault is present in the ROS circuit.
If the fault is present, the SDM will set a diagnostic trouble code (DTC).
Conditions for Running the DTC
Ignition 1 voltage is within the normal operating voltage range.
Conditions for Setting the DTC
B3855
| • | A valid ID message is not received within 5 seconds of the ROS being powered up. |
| • | A status message is not received. |
B3856
| • | The SDM has received a NOK message from the ROS. |
| • | A ROS internal fault exists for a 127 ignition cycles. |
B3857
Will set when the SDM has received an ID message from the ROS that does not match the ID stored in the SDM memory.
Action Taken When the DTC Sets
The SDM commands ON the AIR BAG warning lamp via class 2 serial data.
Conditions for Clearing the DTC
| • | The DTC will clear when the condition responsible for setting the DTC no longer exists and the scan tool Clear DTCs function is used. |
| • | A history DTC will clear once 250 malfunction-free ignition cycles have occurred. |
Diagnostic Aids
The following are conditions that may cause the malfunction:
| • | A short to ground or voltage in the ROS circuit |
| • | High or low resistance in the ROS circuit |
| • | Improper ROS installed on vehicle |
Reference Information
Schematic Reference
SIR Schematics
Connector End View Reference
SIR Connector End Views
Electrical Information Reference
Circuit/System Testing
- If DTC B3856 or B3857 is current, replace the ROS.
- Test the signal and voltage circuits between the SDM and ROS for a short to voltage, short to ground, or open/low resistance. Verify that a short to voltage, short to ground, or open/low resistance does not exist.
| ⇒ | If any of the above conditions are found make the appropriate repair. |
- Reconnect all SIR components. Ignition ON, use the scan tool to clear the DTCs then recheck for DTCs. Verify DTC B3855 does not set.
| ⇒ | If DTC B3855 was current, replace the ROS. After replacement, refer to Repair Verification. |
Repair Instructions
Repair Verification
Ignition ON, use the scan tool to clear the DTC, then recheck for DTC.
| ⇒ | If DTC B3855 was current replace the SDM. |
