DTC B3855, B3856, or B3857. Isuzu Ascender

For 1990-2009 cars only

Makes 🢒 Isuzu 🢒 2007 🢒 Ascender - 2WD 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC B3855, B3856, or B3857

Diagnostic Instructions

•	Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

•	Review Strategy Based Diagnosis for an overview of the diagnostic approach.

•	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

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 Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

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

•	Inflatable Restraint Vehicle Rollover Sensor Replacement

•	SIR/SRS Wiring Repairs

•	Control Module References 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.