B3855

DTC B3855, B3856, or B3857

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.



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 condition responsible for setting the DTC no longer exists.
* A history DTC will clear once 100 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 ([1][2]Air Bag Systems)
Connector End View Reference

Component Connector End Views (Component Connector End Views)
Description and Operation

SIR System Description and Operation (Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)



Circuit/System Testing

1. If DTC B3856 or B3857 is current, replace the ROS.
2. 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.

3. 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

* Inflatable Restraint Vehicle Rollover Sensor Replacement (Inflatable Restraint Vehicle Rollover Sensor Replacement)
* SIR/SRS Wiring Repairs (Component Tests and General Diagnostics)
* Control Module References (Programming and Relearning)for SDM replacement, setup, and programming



Repair Verification

Ignition ON, use the scan tool to clear the DTC, then recheck for DTC.

If DTC B3855 was current replace the SDM.