B1274

Step 1: Perform visual inspection of the vent door actuator and its wiring harness, checking for obvious damage, chafing against metal surfaces, or moisture intrusion at connectors. Pay special attention to areas where harness passes through firewall or near moving components.

Step 2: Disconnect the vent door actuator connector and use a digital multimeter to measure resistance between the potentiometer signal wire and battery positive terminal (should read infinite/OL resistance). Also measure voltage on the signal wire at the harness side with ignition on (should read 0V with actuator disconnected).

Step 3: With actuator still disconnected, check resistance of the potentiometer inside the actuator between signal wire and ground (typically 1-10k ohms depending on position). Manually rotate actuator shaft through full range and verify smooth resistance change with no jumps or shorts to battery voltage.

Step 4: If wiring tests good, install known-good actuator and verify proper operation. If problem persists with new actuator and good wiring, perform BCM output circuit test by measuring voltage commanded to actuator during operation (should vary smoothly, not constant battery voltage).

Step 5: Clear codes, cycle HVAC through all vent positions using climate controls, and verify code does not return. Confirm proper airflow direction at all vent settings to validate repair.