B1786 – Mirror Passenger Down Circuit Failure

The ODBII code B1786 indicates a failure in the passenger side mirror’s down circuit, meaning there is a malfunction preventing the mirror from moving down as intended.

The severity of ODBII code B1786 is moderate.

Common Causes For: B1785 Mirror Passenger Up Circuit Short To Ground

• Faulty passenger side mirror switch
• Damaged wiring or connectors in the mirror circuit
• Defective passenger side mirror motor
• Short circuit in the mirror down circuit
• Blown fuse related to the mirror system
• Corrosion or poor connections in the wiring harness
• Malfunctioning body control module (BCM)

Common misdiagnosis for B1786 Mirror Passenger Down Circuit Failure

• Faulty window switch
• Wiring issues or shorts
• Defective power window motor
• Malfunctioning body control module (BCM)
• Incorrectly installed or damaged door panel
• Issues with the driver’s side window control
• Faulty relay or fuse related to window operation

Common Troubleshooting Steps

The OBD-II code B1786 indicates a “Mirror Passenger Down Circuit Failure.” This code typically relates to issues with the power mirror system, specifically the circuit that controls the downward movement of the passenger side mirror. Here are some common troubleshooting steps to diagnose and potentially resolve this issue:

• Check for Additional Codes: Use an OBD-II scanner to check for any other related trouble codes. This can provide more context and help identify if there are multiple issues.
• Inspect the Wiring and Connectors: Visually inspect the wiring harness and connectors associated with the passenger side mirror. Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the wires that control the mirror’s movement.
• Test the Mirror Switch: The mirror control switch may be faulty. Test the switch for continuity using a multimeter. If the switch is not functioning properly, it may need to be replaced.
• Check the Power Supply: Ensure that the mirror is receiving power. Use a multimeter to check for voltage at the mirror connector when the switch is activated.
• If there is no power, trace the circuit back to the fuse box and check for blown fuses or faulty relays.
• Inspect the Mirror Motor: The mirror motor itself may be defective. If possible, test the motor by applying direct power to it to see if it operates. If it does not move, the motor may need to be replaced.
• Check for Ground Issues: Ensure that the ground connection for the mirror circuit is secure and free of corrosion. A poor ground can cause various electrical issues.
• Look for Short Circuits: Inspect the circuit for any signs of short circuits. This can occur if wires are pinched or damaged, causing them to touch each other or the vehicle chassis.
• Consult Wiring Diagrams: Refer to the vehicle’s service manual for wiring diagrams specific to the mirror circuit. This can help you understand the circuit layout and identify potential problem areas.
• Perform a System Reset: Sometimes, clearing the code and resetting the system can resolve temporary glitches. Use the OBD-II scanner to clear the code and see if it returns.
• Seek Professional Help: If the issue persists after performing these steps, it may be best to consult a professional mechanic or an automotive electrician for further diagnosis and repair. By following these troubleshooting steps, you should be able to identify the cause of the B1786 code and take appropriate action to resolve the issue.