GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2006 🢒 Envoy - 4WD 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 DTC B3855, B3856, or B3857

Circuit 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).

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC B3855 Rollover Sensor Performance
    • DTC B3856 Discard Rollover Sensor
    • DTC B3857 Incorrect Rollover Sensor Installed

Conditions for Running the DTC

Ignition 1 voltage is within the normal operating voltage range of 9-16 volts.

Conditions for Setting the DTC
    • DTC B3855 will set when one of the following conditions occur:
       - A valid ID message is not received within 5 seconds of the ROS being powered up.
       - A status message is not received.
    • DTC B3856 will set when one of the following conditions occur:
       - The SDM has received a NOK message from the ROS.
       - A ROS internal fault exists for a 127 ignition cycles.
    • DTC 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

Thoroughly inspect the wiring and the connectors. An incomplete inspection of the wiring and connectors may result in misdiagnosis, causing a part replacement with the reappearance of the malfunction. If an intermittent malfunction exists, refer to Testing for Intermittent Conditions and Poor Connections .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests the ROS signal and ROS voltage circuits for an open or high resistance.

    2.

  2. This step tests between the ROS signal and ROS voltage circuits for continuity.

    3.

  3. This step tests the ROS signal circuit for a short to voltage.

Step

Action

Yes

No

Schematic Reference: SIR Schematics

Connector End View Reference: SIR Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Use the scan tool to request SIR DTCs displayed.

Does the scan tool indicate that DTC B3856, or B3857 is current?

Go to Step 10

Go to Step 3

3

  1. Turn OFF the ignition.
  2. 2. If DTC B3855 is current, disconnect the inflatable restraint rollover sensor (ROS) connector. Refer to Inflatable Restraint Vehicle Rollover Sensor Replacement .
  3. Inspect both the component and harness sides of the connector for damage or corrosion. Refer to Testing for Intermittent Conditions and Poor Connections .

Does the connector exhibit any signs of damage or corrosion?

Go to Step 4

Go to Step 5

4
  1. If the component side of the ROS connector is damaged, the ROS must be replaced. Refer to Inflatable Restraint Vehicle Rollover Sensor Replacement .
  2. If the harness side of the ROS connector is damaged, replace the harness side of the connector. Refer to Connector Repairs .

Did you complete the repair?

Go to Step 11

--

5
  1. Turn OFF the ignition.
  2. Disconnect the inflatable restraint sensing and diagnostic module (SDM) connector. Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement .
  3. Inspect both the component and harness sides of the SDM connector for damage or corrosion. Refer to Testing for Intermittent Conditions and Poor Connections .

Does the connector exhibit any signs of damage or corrosion?

Go to Step 6

Go to Step 7

6
  1. If the component side of the SDM connector is damaged, the SDM must be replaced. Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement .
  2. If the harness side of the SDM connector is damaged, replace the harness side of the connector. Refer to Connector Repairs .

Did you complete the repair?

Go to Step 11

--

7

If DTC B3855 is current, test both the ROS signal and ROS voltage circuits for an open or high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 11

Go to Step 8

8

Test for continuity between the ROS signal circuit and the ROS voltage circuit on the ROS connector. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 11

Go to Step 9

9

  1. Turn ON the ignition, with the engine OFF.
  2. Test the ROS signal for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 11

Go to Step 10

10
  1. Turn OFF the ignition.
  2. If DTC B3855, B3856, or B3857 was current replace the ROS. Refer to Inflatable Restraint Vehicle Rollover Sensor Replacement .

Did you complete the replacement?

Go to Step 11

--

11
  1. Reconnect all SIR components.
  2. Use the scan tool in order to Clear the DTCs.
  3. Operate the vehicle within the Conditions for Running the DTC as specified in the text.

Does the DTC reset?

Go to Step 12

System OK

12
  1. Turn OFF the ignition.
  2. Replace the SDM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 13

--

13
  1. Turn ON the ignition, with the engine OFF
  2. Use the scan tool in order to Clear the DTCs.
  3. Operate the vehicle within the Conditions for Running the DTC as specified in the text.

Does the DTC reset?

Go to Step 2

System OK