'03 Model:

Check the No. 8 (7.5A) fuse in the driver's under-dash fuse/relay box and the No. 10 (10A) fuse in the passenger's under-dash fuse/relay box.
Are the fuses OK?
1. YES -Go to step 2.
2. NO -Find and repair the cause of the blown fuse.
Remove the OnStar control unit (see ONSTAR CONTROL UNIT INPUT TEST/REPLACEMENT ).
Check for continuity between the B16 terminal of the OnStar control unit and body ground.
Is there continuity?
1. YES -Go to step 4.
2. NO -Repair open in the BLK wire between the OnStar control unit and G551.
With the ignition switch OFF, press and hold the "dot" button. Turn the ignition switch from OFF to ACC three times and back to ACC, then release the "dot" button.
The indicator will flash (green or red) if any failures have been detected. Troubleshoot the DTCs as indicated below:

Fig 1: Identifying DTCs
Courtesy of AMERICAN HONDA MOTOR CO., INC.

NOTE:

Green indicator flashes historic (stored) failure DTCs.
Red indicator flashes current failure DTCs.
Current DTCs, are displayed first, followed by history DTCs, if any.
DTCs are displayed in numerical order for two cycles. The indicator returns to normal function after the two cycles.

Example: When DTC1 and DTC2 are detected

Fig 2: Indicator Showing DTC1 and DTC2

Courtesy of AMERICAN HONDA MOTOR CO., INC.