GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 DTC 🢒 DTC B0077, B0079, or B0080

Circuit Description

The inflatable restraint electronic frontal sensor (EFS) utilizes a unidirectional 2-wire circuit. The EFS 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 EFS. When the ignition is turned on and input power from the SDM is first detected, the EFS 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 EFS continually communicates status messages to the SDM, which determines if a fault is present in the EFS circuit. When a fault is detected, the SDM resets the EFS twice by removing and reapplying power. If the fault is still 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
    • DTC B0077 will set when one of the following conditions occur:
       - A valid ID message is not received within 5 seconds of the EFS being powered up.
       - Status message is not received.
       - The SDM has failed twice to reset the EFS.
    • DTC B0079 will set when one of the following conditions occur:
       - The SDM has received an ID message from the EFS which does not match the ID stored in the SDM memory.
       - When two EFS resets are attempted without the correct identification being detected by the SDM.
    • DTC B0080 will set when the SDM has received a NOK (Not OK) message from the EFS.

Action Taken When the DTC Sets
    • The SDM commands ON the AIR BAG indicator via Class 2 serial data.
    • The SDM attempts to reset the EFS.

Conditions for Clearing the DTC
    • The condition responsible for setting the DTC no longer exists.
    • You issue a scan tool CLEAR DTCs command.
    • A history DTC will clear once 255 malfunction free ignition cycles have occurred.

Diagnostic Aids

The following can cause an intermittent condition:

    • A short between the EFS signal and voltage circuits
    • High or low resistance in the EFS signal and voltage circuits
    • Inspect the EFS signal and voltage circuits carefully for cutting and/or chafing
    • Verify that the correct EFS is installed in the vehicle

Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

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

  1. Tests the communication status of the EFS.

    2.

  2. Tests for a short to ground, a high resistance, or an open in the EFS signal circuit.

    3.

  3. Tests for a short to ground, a high resistance, or an open in the EFS voltage circuit.

    4.

  4. Tests for a short to voltage in the EFS signal and voltage circuits.

Step

Action

Yes

No

Schematic Reference: SIR Schematics

1

Did you perform the Diagnostic System Check - SIR?

Go to Step 2

Go to Diagnostic System Check - SIR

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, request the SIR DTC display.

Does the scan tool indicate that either DTC B0079, or B0080 is current?

Go to Step 12

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Disconnect the EFS connector. Refer to Inflatable Restraint Front End Discriminating Sensor Replacement .
  3. Inspect both the EFS and harness connector terminals for damage or corrosion. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Does the EFS terminals or harness connector exhibit any signs of damage or corrosion?

Go to Step 4

Go to Step 5

4
  1. If the EFS terminals are damaged, replace the EFS. Refer to Inflatable Restraint Front End Discriminating Sensor Replacement .
  2. If the EFS harness connector is damaged, replace the connector. Refer to Connector Repairs in Wiring Systems.

Did you complete the replacement?

Go to Step 13

--

5
  1. Disconnect the SDM connector. Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement .
  2. Inspect the SDM connector for corrosion or damage. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 6

6

Test the EFS signal circuit for a short to ground, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 7

7

Test the EFS voltage circuit for a short to ground, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 8

8

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

Did you find and correct the condition?

Go to Step 13

Go to Step 9

9

Replace the EFS. Refer to Inflatable Restraint Front End Discriminating Sensor Replacement .

Did you complete the replacement?

Go to Step 10

--

10
  1. Reconnect all SIR system 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 supporting text.

Does the DTC reset?

Go to Step 11

System OK

11

Replace the SDM. Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement .

Did you complete the replacement?

Go to Step 13

--

12

Replace the EFS. Refer to Inflatable Restraint Front End Discriminating Sensor Replacement .

Did you complete the replacement?

Go to Step 13

--

13
  1. Reconnect all SIR system components.
  2. Verify that all components, connectors and CPAs are properly mounted.
  3. Use the scan tool in order to clear the DTCs.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK