B0077

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 0 Health, and deployment commands to the inflatable restraint sensing and diagnostic module (SDM). The 8DM serves as a power source and a ground for the EFS. When the ignition is turned on and input power from the 8DM is first detected, the EFS responds by performing internal diagnostics and sending an ID to the SDM. The 8DM considers the ID to be valid if the response time is less than 5 seconds. The EFS continually communicates status messages to the 8DM, 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 8DM 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 8DM has received an ID message from the EFS which does not match the ID stored in the 8DM memory.
- When two EFS resets are attempted without the correct identification being detected by the 8DM.
^ DTC B0080 will set when the 8DM 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 left 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 left EFS signal and voltage circuits
^ High or low resistance in the left EFS signal and voltage circuits
^ Inspect the left EFS signal and voltage circuits carefully for cutting and/or chafing

Refer to Testing for Intermittent and Poor Connections in Diagrams.

TEST DESCRIPTION

Steps 1-2:

Steps 3-13:

The numbers below refer to the step numbers on the diagnostic table:
2. Tests for a short to ground, a high resistance, or an open in the left EFS signal circuit.
6. Tests for a short to ground, a high resistance, or an open in the left EFS voltage circuit.
7. Tests for a short to voltage in the left EFS signal circuit.
8. Tests for a short to voltage in the left EFS voltage circuit.