For 1990-2009 cars

### Circuit Description

When the ignition is turned on, the SDM performs a self-test to diagnose malfunctions inside the module. The SDM provides input power to the SIS. When the input power is first detected, the SIS responds by performing internal diagnostics. Next the SIS sends an ID message to the SDM. The SDM will consider this to be a valid ID if the response time is less than 5 seconds after the SIS is powered up. The SIS will continually communicate a status message to the SDM. The SDM can reset the SIS by removing and applying power to it.

### Conditions for Setting the DTC

DTC B0077 can be set when the left SIS malfunctions. The following conditions must be met to set this DTC:

• | Ignition voltage is present at the SDM continuous.

• | The SDM detects a left SIS fault.

• | The SDM resets the left SIS twice without detecting correct operation.

### Action Taken When the DTC Sets

• | DTC B0077 will set.

• | The air bag telltale will be on.

### Diagnostic Aids

• | When attempting to diagnose an intermittent passenger loop fault, use the scan tool to monitor the current DTCs. Wiggle the wires and check the connections while watching for a current DTC to appear and/or disappear on the scan tool.

• | Always start diagnosis of the SIR DTCs with an inspection of the wiring and the SIR components for visible damage.

• | A short to ground in circuits 2131 or 2132 and another vehicle circuit could casue this DTC.

• | Always perform the Diagnostic System Check - SIR .

### B0077