B1792

Step 1: Perform visual inspection of autolamp sensor (typically located on dashboard near windshield or integrated into rearview mirror). Check for physical damage, moisture intrusion, or connector damage. Disconnect sensor connector and inspect pins for corrosion, bent terminals, or evidence of overheating.

Step 2: Using a digital multimeter, backprobe the BCM side of the disconnected autolamp sensor harness connector. Measure voltage on the signal wire (typically reference voltage should be 0-5V range). If battery voltage (12V+) is present with sensor disconnected, wiring harness has a short to power.

Step 3: If no voltage present at BCM connector with sensor disconnected, measure resistance of the autolamp sensor itself. Connect ohmmeter across sensor signal pin and ground pin. A properly functioning sensor should show variable resistance when exposed to different light levels (typically 500 ohms to 50k ohms range). If resistance is near zero ohms or sensor shows battery voltage on signal pin, sensor is internally shorted.

Step 4: Trace wiring harness from autolamp sensor to BCM, checking for pinch points, especially near hood hinges, door jambs, and dashboard mounting points. Gently manipulate harness while monitoring voltage to identify intermittent short locations.

Step 5: If all wiring and sensor test normal, perform BCM voltage input test per manufacturer specifications. Monitor BCM sensor input circuit with multimeter while cycling ignition. If BCM shows erratic voltage readings with known-good sensor and wiring, BCM may require replacement or reprogramming.

Step 6: After repair (sensor replacement, wiring repair, or connector repair), clear codes, verify proper autolamp operation by covering sensor and observing headlamp activation. Road test through various lighting conditions and rescan for code return.