B1787 – Mirror Passenger Down Circuit Open

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The ODBII code B1787 indicates that there is an open circuit in the passenger side mirror’s down movement function, meaning the system is unable to detect or control the downward movement of the passenger side mirror.

The severity of ODBII code B1787 is moderate.

Common Causes For: B1786 Mirror Passenger Down Circuit Failure

  • Faulty passenger side mirror switch
  • Damaged wiring or connectors in the mirror circuit
  • Failed passenger side mirror motor
  • Blown fuse related to the mirror circuit
  • Poor ground connection for the mirror system
  • Corrosion or dirt in the connector terminals

Common misdiagnosis for B1787 Mirror Passenger Down Circuit Open

  • Faulty window switch
  • Broken wiring or connectors
  • 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 B1787 indicates a problem with the passenger side mirror’s down circuit, specifically that it is open. This means that the circuit responsible for moving the passenger side mirror down is not functioning properly. Here are some common troubleshooting steps to diagnose and potentially resolve the issue:

  • Check the Vehicle’s Manual: Refer to the vehicle’s service manual for specific information about the mirror circuit and wiring diagrams.
  • Visual Inspection:
  • Inspect the wiring harness and connectors leading to the passenger side mirror for any signs of damage, corrosion, or loose connections.
  • Look for any frayed wires or broken connectors that could cause an open circuit.
  • Test the Mirror Switch:
  • Use a multimeter to test the mirror control switch. Ensure that it is functioning correctly and sending the appropriate signals to the mirror.
  • If the switch is faulty, it may need to be replaced.
  • Check the Mirror Motor:
  • Test the passenger side mirror motor by applying direct power to it. If the motor does not respond, it may be defective and require replacement.
  • Inspect Fuses:
  • Check the fuses related to the power mirrors. A blown fuse could interrupt the circuit and cause the code to trigger.
  • Scan for Additional Codes:
  • Use an OBD-II scanner to check for any additional trouble codes that may provide more context or indicate related issues.
  • Check Ground Connections:
  • Ensure that the ground connections for the mirror circuit are secure and free of corrosion. A poor ground can lead to circuit issues.
  • Perform a Continuity Test:
  • Use a multimeter to perform a continuity test on the wiring from the mirror switch to the mirror motor. This will help identify any breaks in the circuit.
  • Inspect the Body Control Module (BCM):
  • If all other components check out, the issue may lie within the BCM. Ensure that it is functioning correctly and that there are no software issues.
  • Clear the Code and Test Drive:
  • After performing repairs or replacements, clear the trouble code using an OBD-II scanner and take the vehicle for a test drive to see if the code returns. If you are not comfortable performing these steps or if the issue persists after troubleshooting, it may be best to consult a professional mechanic for further diagnosis and repair.

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