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DTC B2647: Ambient Lamp Sensor Circuit Low: Testing

WARNING: This page is about a different car, the 1999 Pontiac Grand Am and 1999 Oldsmobile Alero. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: If circuit is shorted to ground, fuse will blow. Check fuse before performing diagnostics.
  1. Perform BCM DIAGNOSTIC SYSTEM CHECK  under SYSTEM TESTS. Go to next step.
  2. Disconnect ambient light sensor. Sensor is located on top of the instrument panel near defroster vents. Disconnect BCM connector C2. Using DVOM, measure resistance between ambient light sensor connector terminal "B" (Yellow/Black wire) and ground. See WIRING DIAGRAMS  . If no resistance (infinite) is indicated, go to step  4 . If any resistance is indicated, go to next step.
  3. Repair short to ground in Yellow/Black wire between BCM and ambient light sensor. After repairs, go to step  7 .
  4. Using DVOM, measure resistance of Yellow/Black wire between BCM and ambient light sensor. If reading is less than 2 ohms, go to step  9 . If reading is greater than 2 ohms, go to next step.
  5. Repair open in Yellow/Black wire between BCM and ambient light sensor. After repairs, go to BCM DIAGNOSTIC SYSTEM CHECK  under SYSTEM TESTS.
  6. Replace ambient light sensor. After repairs, go to next step.
  7. Using scan tool, clear DTCs. If DTC does not reset, go to BCM DIAGNOSTIC SYSTEM CHECK  under SYSTEM TESTS. If DTC resets, go to next step.
  8. Replace BCM. See BODY CONTROL MODULE  under REMOVAL & INSTALLATION. After repairs, go to BCM DIAGNOSTIC SYSTEM CHECK  under SYSTEM TESTS.
  9. Using DVOM, measure resistance of Light Green/Black wire between BCM and ambient light sensor. If reading is less than 2 ohms, go to step  11 . If reading is greater than 2 ohms, go to next step.
  10. Repair open in Light Green/Black wire between BCM and ambient light sensor. After repairs, go to step  7 .
  11. Using DVOM, measure resistance in Light Green/Black wire between BCM and ambient light sensor. If reading is less than 2 ohms, go to step  6 . If reading is greater than 2 ohms, go to next step.
  12. Repair short to ground in Light Green/Black wire between BCM and ambient light sensor. After repairs, go to step  7 .
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