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 MANUALSOLDSMOBILE1998ACHIEVA 3.1 M, 4T40E/MN4REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 5 (BODY CONTROL MODULES)DIAGNOSTIC TESTSDTC B2647: AMBIENT LAMP SENSOR CIRCUIT LOWTESTING
1998 Oldsmobile Achieva 3.1 M, 4T40E/MN4
DTC B2647: Ambient Lamp Sensor Circuit Low: Testing
1998 Oldsmobile Achieva 3.1 M, 4T40E/MN4SECTION 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.
- Perform BCM DIAGNOSTIC SYSTEM CHECK under SYSTEM TESTS. Go to next step.
- 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.
- Repair short to ground in Yellow/Black wire between BCM and ambient light sensor. After repairs, go to step 7 .
- 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.
- Repair open in Yellow/Black wire between BCM and ambient light sensor. After repairs, go to BCM DIAGNOSTIC SYSTEM CHECK under SYSTEM TESTS.
- Replace ambient light sensor. After repairs, go to next step.
- 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.
- Replace BCM. See BODY CONTROL MODULE under REMOVAL & INSTALLATION. After repairs, go to BCM DIAGNOSTIC SYSTEM CHECK under SYSTEM TESTS.
- 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.
- Repair open in Light Green/Black wire between BCM and ambient light sensor. After repairs, go to step 7 .
- 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.
- 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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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.