A Diagnostic System Check

Diagnostic Chart:

CIRCUIT DESCRIPTION
Voltage is applied at all times from the POWER ACCY Fuse 7 through circuit 640 to the SECURITY indicator lamp on the instrument cluster.

Ground is applied by the Body Control Module (BCM) through circuit 728 to the SECURITY indicator lamp when the ignition switch is in the RUN or BULB TEST position.

When the ignition switch is turned to the RUN or BULB TEST position, the SECURITY indicator lamp illuminates for approximately 5 seconds in order to verify the circuit operation.

The BCM also uses the SECURITY indicator lamp in order to display the DTC flash codes by grounding CKT 728.

CONDITIONS FOR SETTING THE DTC
DTC 12 is always set and displayed when the Body Control Module (BCM) is in the diagnostic mode. DTC 12 indicates that the diagnostic function is in progress. If DTC 12 does not display when the BCM is in the diagnostic mode, refer to the following diagnostic chart.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
1. This step tests the SECURITY indicator lamp operation at the BULB TEST.
2. This step tests the BCM operation in the diagnostic mode.
3. This step tests the BCM output to the retained accessory power (RAP) components.
4. This step tests circuit 75 for a short to ground.
5. This step tests the BCM operation in the diagnostic mode after the repair to circuit 75.
7. If the SECURITY indicator lamp does not illuminate, this step determines if the fault is in the BCM or the SECURITY indicator circuit.
8. This step tests for a poor connection at the BCM.
9. This step tests for an open in circuit 640.
10. This step tests for an open in circuit 728.