GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Sierra Denali 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC B0091

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 B0091 00: Front End Sensor 3 No Additional Information

DTC B0091 01: Front End Sensor 3 Short to Battery

DTC B0091 02: Front End Sensor 3 Short to Ground

DTC B0091 05: Front End Sensor 3 Short to Battery or Open

DTC B0091 0F: Front End Sensor 3 Erratic

DTC B0091 39: Front End Sensor 3 Internal Electronic Failure

DTC B0091 3A: Front End Sensor 3 Incorrect Component Installed

DTC B0091 71: Front End Sensor 3 Invalid Serial Data Received

Circuit/System Description

The inflatable restraint front end sensor utilizes a unidirectional 2-wire circuit. The front end sensor modulates current on the interface to send ID, state of health, and deployment commands to the inflatable restraint sensing and diagnostic module (SDM). The SDM serves as a power source and a ground for the front end sensor. When the ignition is turned ON and input power from the SDM is first detected, the front end sensor responds by performing internal diagnostics and sending an ID to the SDM. The SDM considers the ID to be valid if the response time is less than 5 seconds. The front end sensor continually communicates status messages to the SDM, which determines if a fault is present in the front end sensor circuit. When a fault is detected, the SDM may reset the front end sensor up to 2 times by removing and reapplying power to it. If the fault is still present, the SDM will set a DTC.

Conditions for Running the DTC

Ignition voltage is between 9-16 volts.

Conditions for Setting the DTC

B0091 00

    • The front end sensor has been shorted to voltage, open, or shorted to ground.
    • The front end sensor current has been above 23 mA for longer than 5 milliseconds.
    • The SDM has not received a message from the front end sensor for more than 375 milliseconds.

B0091 01

    • The front end sensor has been shorted to voltage.
    • The front end sensor current has been above 23 mA for longer than 5 milliseconds.
    • The SDM has not received a message from the front end sensor for more than 375 milliseconds.

B0091 02

    • The front end sensor has been shorted to ground.
    • The front end sensor current has been above 23 mA for longer than 5 milliseconds.
    • The SDM has not received a message from the front end sensor for more than 375 milliseconds.

B0091 05

    • The front end sensor has been shorted to voltage.
    • The front end sensor circuit is open.
    • The front end sensor current has been above 23 mA for longer than 5 milliseconds.
    • The SDM has not received a message from the front end sensor for more than 375 milliseconds.

B0091 0F

The SDM has received erratic messages from the front end sensor.

B0091 39

    • The SDM has received a NOK message from the front end sensor.
    • The SDM has not received a message.

B0091 3A

    • The SDM has received an ID message from the front end sensor, which does not match the ID stored in the SDM memory.
    • The SDM has reset the front end sensor twice without detecting the correct ID message.

B0091 71

The SDM has received invalid serial data from the front end sensor.

Action Taken When the DTC Sets
    • The SDM commands the AIR BAG indicator ON via serial data communications.
    • The frontal SIR System is disabled and no frontal deployments are allowed. Side deployments and rollover detection is still enabled.

Conditions for Clearing the DTC
    • 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 100 malfunction-free ignition cycles have occurred.

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

    Important: When removing connectors, inspect for damage or corrosion. Damage or corrosion in the following requires repair or replacement of the affected component/connector:

       • The front end sensor
       • The SDM module
       • The front end sensor wiring harness connector
       • The SDM wiring harness connector

  1. Ignition OFF, disconnect the appropriate front end sensor connector. Refer to front end sensor replacement for location of connector.
  2. Remove the SDM connector. Refer to SDM replacement for location of connector.
  3. Test for infinite resistance between the signal circuit and ground.
    4. ⇒If less than infinite resistance, test the circuit for a short to ground.
  4. Ignition ON, test for less than 1 volt between the front end sensor signal circuit and ground.
    5. ⇒If greater than the specified range, test the circuit for a short to voltage.
  5. Ignition ON, test for less than 1 volt between the front end sensor low reference circuit and ground.
    6. ⇒If greater than the specified range, test the circuit for a short to voltage.
  6. Test for less then 1 ohm of resistance between the signal circuit front end sensor connector and SDM connector.
    7. ⇒If greater than the specified range, test the circuit for an open/high resistance.
  7. Test for less then 1 ohm of resistance between the low reference circuit front end sensor connector and SDM connector.
    8. ⇒If greater than the specified range, test the circuit for an open/high resistance.
  8. If the circuits test normal, replace the appropriate front end sensor.
  9. Reconnect all SIR components. Ignition ON, with a scan tool clear and recheck for DTCs.
    10. ⇒If the front end sensor DTC returns and is current, replace the SDM.

Repair Instructions
    •  Inflatable Restraint Front End 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 DTCs, then recheck for DTCs.

⇒If DTC B0091 was current, replace the SDM.