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 input power is first
detected, the SIS responds by performing internal diagnostics. Next the SIS sends
and 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:
| • | The 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
| • | 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 wiring and
the SIR components for visible damage. |
| • | A short to ground in the circuits 2131 or 2132 and another vehicle circuit
could cause this DTC. |
B0077
