B3856
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
Diagnostic Fault Information
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 voltage is between 9-16 volts.
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 requests the instrument panel cluster (IPC) to illuminate the AIR BAG indicator.
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.
Reference Information
Schematic Reference
SIR Schematics ([1][2]Air Bag Systems)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
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)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Testing
1. Ignition ON, if B3856 or B3857 is current, replace the rollover sensor.
2. Ignition OFF, disconnect the harness connector at the rollover sensor and the SDM.
3. Test for less than 1.0 ohm between the ground circuit terminal 6 and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
4. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 1 and ground.
• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
5. Test for less than 1 volt between the serial data circuit terminal 5 and ground.
• If greater than the specified range, test the serial data circuit for a short to voltage.
6. Ignition OFF, test for infinite resistance between the serial data circuit terminal 5 and ground.
• If less than the specified value, test the serial data circuit for a short to ground.
7. Test for less than 1 ohm between the rollover sensor terminal 5 and SDM terminal 35.
• If less than the specified value, test the serial data link for an open/high resistance.
8. If all circuits test normal, replace the rollover sensor.
• If the DTC resets as current, replace the SDM.
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.