B1781

Step 1: Perform visual inspection of driver's door mirror wiring harness, especially in door jamb flex area. Look for pinched, chafed, or damaged wires that may be contacting metal surfaces. Check connector at mirror housing for water intrusion, corrosion, or pushed-out pins.

Step 2: Disconnect the driver's side mirror electrical connector. Using a digital multimeter, measure resistance between the mirror down motor circuit wire (consult wiring diagram for specific pin) and chassis ground. Reading should be infinite ohms (open circuit). If reading shows continuity or low resistance, wiring harness is shorted to ground.

Step 3: If wiring checks good, test the mirror motor itself by measuring resistance across the mirror down motor terminals with mirror disconnected. Typical resistance should be 3-15 ohms. Also check for continuity between motor terminals and mirror housing ground. Any continuity indicates internal motor short.

Step 4: If both wiring and mirror motor test good, check for proper voltage supply and ground at mirror connector with key on using multimeter or test light. Command mirror down using switch while monitoring circuit. Verify control module is providing proper switched voltage.

Step 5: If all external components test good, suspect door control module or BCM internal driver circuit failure. Check technical service bulletins for known module issues. May require module replacement or reprogramming if all other components verified functional.

Step 6: After repair, clear codes, cycle mirror through full range of motion multiple times, and verify code does not return. Test mirror operation in all directions to confirm proper function.