SVS Message, DTC B2647 and/or B2648 Set (Replace Body Control Module)

Some customers may comment about a "Service Vehicle Soon" message displayed, which may or may not store diagnostic codes (DTCs) B2647 and/or B2648.

The headlamp auto control ambient light sensor sends a brief voltage spike to the body control module (BCM) during engine crank, which may be detected as a fault by the BCM. This may initiate the SVS message. This voltage is considered a normal condition of the ambient light sensor.

Replace the body control module (BCM) to correct this condition.

BCM replacement is not complete until the BCM is configured to the vehicle and the vehicle theft deterrent re-learn is completed. Without BCM configuration, the radio will display locked (Theft Lock Enabled) and the vehicle's engine will not crank (Vehicle Theft Deterrent Enabled). The radio theft lock system compares the VIN in the BCM with the VIN in the radio. If the VIN was not entered in the BCM at the time of replacement/configuration, the radio will display "Locked". If the vehicle theft deterrent procedure is not completed properly, the engine will not crank when the key is turned to the crank position.

Important: If the module is not properly configured within twenty (20) key cycles (including the VIN), the module will lock and configuring will not be allowed. For this reason, replacing the module with a module from another vehicle will not work. They cannot be reconfigured.

When replacing the BCM, a critical component of the procedure requires a configuring of the BCM. To configure the BCM, follow all of the steps in the procedure listed below.

Important: Before starting this procedure, read through it carefully and completely.

Configuring of the BCM requires the use of the Tech 2 scan tool.

Ensure that the Tech 2 has been updated.

Begin the service procedure with the original BCM in the vehicle.

1. Set the parking brake. This will keep the headlamps and/or the daytime running lamps OFF.
2. Connect the Tech 2 scan tool to the Data Link Connector (DLC).
3. Turn the ignition key to the ON/RUN position. Do not start the engine.
4. Press the Power key on the Tech 2.
5. Press the Enter key on the Tech 2.
6. Select Diagnostics and press Enter.
7. Select Model Year 2000 and press Enter.
8. Select Passenger Car and press Enter.
9. Select Body and press Enter.
10. Select W as the Car Product Line and press Enter.
11. Select Chevrolet and press Enter.
12. Select the proper vehicle and press Enter.
13. Select Body Control Module and press Enter.
14. Select Special Functions and press Enter.
15. Select Set Options and press Enter.
16. Select Set Option Configuration and press Enter.
17. Press the key under the highlighted Done area of the Tech 2 display.
18. The setting option screen will display the options currently set in this vehicle. Record the Tech 2 display of the special options highlighted with an asterisk (*). You will need to re-enter this information in a later step.
19. Press the key under the highlighted Save Options area on the Tech 2 screen. A Loss of Communications message will display on the Tech 2 (ignore this message).
20. Press Exit.
21. Turn the ignition key to the OFF position.
22. Disconnect the Tech 2 from the vehicle's DLC.
23. Remove the LH sound insulator panel located under the dash.
24. Disconnect the three BCM wiring connectors.
25. Remove the BCM from the vehicle.
26. Install the new BCM in the vehicle.
27. Connect the three wiring harness connectors to the BCM.
28. Install the LH sound insulator panel.
29. Connect the Tech 2 scan tool to the DLC.
30. Turn the ignition key to the ON/RUN position.
31. Press the Power key on the Tech 2.
32. Press the Enter key on the Tech 2.
33. Select Diagnostics and press Enter.
34. Select Model Year 2000 and press Enter.
35. Select Passenger Car and press Enter.
36. Select Body and press Enter.
37. Select W as the Car Product Line and press Enter.
38. Select Chevrolet and press Enter.
39. Select the proper vehicle and press Enter.
40. Select Body Control Module and press Enter.
41. Select Special Functions and press Enter.
42. Select New VIN and press Enter.
43. Enter the correct VIN.
44. Press Exit until you are back to the Special Functions screen.
45. Select BCM Programming and press Enter.
46. Select Set-Up BCM. Press the key under the highlighted Set-Up BCM on the Tech 2.

The Tech 2 will display the following message: NOW SETTING UP THE NEW BODY CONTROL MODULE.

47. A Body Control Setup Complete message will appear on the display. Press the key under the highlighted Exit.
48. Select Set Options and press Enter.
49. Select Point of Sale and press Enter. The setting options screen will appear again. Press the key under the highlighted Done again.
50. Select Domestic under Point of Sale. Press the key under the Save option area on the screen.
51. Select Set Option Configuration and press Enter.
52. Press the key under the highlighted Done area of the Tech 2 display.
53. Select the options you recorded from the original BCM in Step 18. Highlight the option by using the arrow keys on the Tech 2. Press Enter to place an asterisk (*) in front of the option. When all the options have been selected, press the key under the highlighted Save Options area on the Tech 2.
54. Exit back to the Main Menu screen.
55. Remove the Tech 2 from the DLC and the vehicle.

Important: Perform the following theft deterrent re-learn procedure when one or more of the following conditions has occurred:

•	The BCM has been replaced or reprogrammed (set-up, configured).

•	The ignition key cylinder assembly has been replaced.

56. You MUST perform the following manual theft deterrent re-learn procedure. The required procedure has a special step that must be completed or the theft re-learn will not work.
57. Turn the ignition switch to OFF and wait 15 seconds.
58. Turn the ignition switch to START. Hold it in this position until the instrument cluster telltale lamps illuminate (approximately seven seconds). Then release the ignition switch to the RUN position (the engine will not crank).
59. The Security and Battery messages will begin toggling.
60. The ignition key must NOT be disturbed for the next 10 minutes. When the 10 minute time period has elapsed, the Security/Battery telltale will become a solid battery-only lamp.
61. Turn the ignition to OFF. With the PRNDL display off, wait five seconds.
62. Turn the ignition switch to START and hold it in this position until the instrument cluster telltales illuminate (approximately seven seconds). Then release the ignition switch to the RUN position (the engine will not crank).
63. The Security and Battery messages will begin toggling.
64. The ignition key must NOT be disturbed for the next 10 minutes. When the 10 minute time period has elapsed, the Security/Battery telltale will become a solid battery-only lamp.
65. Turn the ignition to OFF. With the PRNDL display off, wait five seconds.
66. Turn the ignition switch to START and hold it in this position until the instrument cluster telltales illuminate (approximately seven seconds). Then release the ignition switch to the RUN position (the engine will not crank).
67. The Security and Battery messages will begin toggling.
68. The ignition key must NOT be disturbed for the next 10 minutes. When the 10 minute time period has elapsed, the Security/Battery telltale will become a solid battery-only lamp.
69. Turn the ignition to OFF. With the PRNDL display off, wait five seconds.
70. Turn the ignition switch to ON and wait 15 seconds before starting the engine.

The BCM part number has not changed, but the new BCM should have a code GMAB139 or higher on the label.

Parts are currently available from GMSPO.

For vehicles repaired under warranty, use: