B2339

Step 1: Perform a visual inspection of the mirror switch assembly and connector for signs of physical damage, liquid intrusion, or corrosion. Check for aftermarket modifications or recent repairs that may have affected the circuit.

Step 2: Using a digital multimeter, disconnect the mirror switch assembly connector and measure resistance to ground on each switch circuit pin at the harness side. All circuits should show infinite resistance (open circuit) with switches in neutral position. Any reading below 10k ohms indicates a short to ground in the wiring.

Step 3: Inspect the driver door wiring harness thoroughly, especially in the door jamb area where wires flex. Look for pinched, chafed, or broken wires. Wiggle test the harness while monitoring resistance to ground to identify intermittent shorts.

Step 4: If wiring tests normal, reconnect the switch and back-probe the connector terminals with the multimeter. Monitor voltage on each switch circuit while operating the mirror controls. Voltage should be stable battery voltage or ground depending on switch position. Erratic readings indicate faulty switch assembly.

Step 5: If all previous tests pass, inspect the BCM connector and terminals for corrosion or damage. Test the BCM inputs by measuring voltage at the BCM connector with switch disconnected (should read pull-up voltage, typically 5V or battery voltage).

Step 6: After repair, clear codes and verify proper mirror operation in all directions. Perform a drive cycle and re-scan to confirm the fault does not return. Check for proper switch response at the BCM using scan tool data stream if available.