Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSBUICK2000CENTURY CUSTOMREPAIR AND DIAGNOSISBODY & FRAMEBODY, CAB CONTROL SYSTEMSBODY CONTROL MODULESDIAGNOSTIC TESTSDTC B2648: AMBIENT LIGHT SENSOR CIRCUIT HIGHTESTING
2000 Buick Century Custom
DTC B2648: Ambient Light Sensor Circuit High: Testing
2000 Buick Century CustomSECTION Testing
- Perform lighting system diagnostic system check. See LIGHTING SYSTEM DIAGNOSTIC SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check, go to next step.
- Turn ignition off. Connect scan tool to DLC. Turn ignition on, with engine off. Use scan tool to observe ambient light sensor parameter in BCM data display list. If scan tool indicates ambient light sensor input is 0.25-2.5 volts, go to DIAGNOSTIC AIDS . If scan tool indicates ambient light sensor input is not 0.25-2.5 volts, go to next step.
- Turn ignition off. Disconnect ambient light sensor electrical connector. Turn ignition on, with engine off. Use scan tool to observe ambient light sensor parameter in BCM data display list. If scan tool indicates ambient light sensor input is greater than 2.5 volts, go to next step. If scan tool indicates ambient light sensor input is not greater than 2.5 volts, go to step 5 .
- Turn ignition off. Connect a 3-amp fused jumper wire between Light Green/Black and Yellow/Black wires of ambient light sensor connector. Turn ignition on, with engine off. Use scan tool to observe ambient light sensor parameter in BCM data display list. If scan tool indicates ambient light sensor input is less than 0.25 volt, go to step 8 . If scan tool indicates ambient light sensor input is not less than 0.25 volt, go to step 6 .
- Test Yellow/Black wire between ambient light sensor connector and BCM harness connector C2 terminal B1 for short to ground. See appropriate HEADLIGHT SYSTEMS & DAYTIME RUNNING LIGHTS wiring diagram. After repair, go to step 12 . If fault is not located and condition still exists, go to step 12 .
- Test Yellow/Black wire between ambient light sensor connector and BCM harness connector C2 terminal B1 for short to battery voltage, high resistance, or an open. See appropriate HEADLIGHT SYSTEMS & DAYTIME RUNNING LIGHTS wiring diagram. After repair, go to step 12 . If fault is not located and condition still exists, go to next step.
- Test Light Green/Black wire between ambient light sensor connector and BCM harness connector C2 terminal B2 for high resistance, or an open. See appropriate HEADLIGHT SYSTEMS & DAYTIME RUNNING LIGHTS wiring diagram. After repair, go to step 12 . If fault is not located and condition still exists, go to step 9 .
- Inspect for poor connections at ambient light sensor. After repair, go to step 12 . If fault is not located and condition still exists, go to step 10 .
- Inspect for poor connections at BCM harness connector C2. After repair, go to step 12 . If fault is not located and condition still exists, go to step 11 .
- Replace ambient light sensor. After repair, go to step 12 .
- Replace BCM. See BODY CONTROL MODULE (BCM) under REMOVAL & INSTALLATION. After replacement, perform set up procedure. See NEW BCM SETUP under PROGRAMMING. After replacement, go to next step.
- Using scan tool, clear BCM DTCs. Operate vehicle within conditions to set DTC. If DTC B2648 resets, return to step 2 . If DTC B2648 does not reset, system is okay.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.