B1787 — Mirror Passenger Down Circuit Open #

Note: The description of this DTC may vary depending on the vehicle manufacturer.

• Mirror Passenger Down Circuit Open (Generic/OEMs)
• Right Side Mirror Down Circuit Open (Toyota/Lexus)
• Passenger Mirror Vertical Motor Circuit Open (Honda/Acura)
• Passenger Mirror Position Sensor Open Circuit (Ford/Lincoln)

Summary of DTC B1787 #

The B1787 code is a Body Control Module (BCM) Diagnostic Trouble Code (DTC) that signals an open circuit in the passenger side mirror’s “down” control wiring. In simple terms, this means the vehicle’s computer has detected a break or lack of continuity in the electrical path that allows you to tilt the right-side (passenger) mirror downward using the mirror adjustment switch. This code can be triggered by wiring issues, connector problems, a failed mirror motor, or faults in the control module itself. While it does not typically affect driving safety, it can make adjusting or auto-tilting the passenger mirror impossible, which may be inconvenient—especially when parking or reversing. Knowing the probable causes and steps to diagnose can help you quickly restore full mirror function.

Common Symptoms for DTC B1787 #

When the B1787 code is active, you may notice certain inconveniences or malfunctions related to your passenger side mirror. Most notably, the ability to move the mirror downward will be lost or inconsistent, but other symptoms may also be present. Recognizing these helps you and your technician zero in on the fault faster:

• Passenger side mirror does not move down when using the adjustment switch
• Mirror only moves up, left, or right, but not down
• Mirrors do not auto-tilt downward when reversing (if equipped with memory/auto-tilt)
• Warning lights or messages related to mirrors on the dashboard
• Clicking or buzzing sounds from the mirror assembly

Most Likely Causes of Code B1787 #

The B1787 DTC generally points to an electrical interruption or open circuit. This can be due to several common causes, ranked here from most to least frequent:

1. Broken or damaged wiring between the BCM and passenger mirror motor
2. Loose or corroded connectors at the mirror, door, or control switch
3. Faulty mirror motor (vertical/down actuator)
4. Malfunctioning mirror adjustment switch
5. Internal fault in the Body Control Module (BCM)
6. Blown fuse related to mirror circuits (rare but possible)

Step-by-Step Diagnosis for B1787 #

Diagnosing B1787 requires a systematic approach to avoid unnecessary parts replacement. Here’s a proven step-by-step method:

1. Scan for codes: Confirm the presence of B1787 and check for related mirror or BCM codes.
2. Test mirror movement: Operate all directions from the switch; note which functions are lost.
3. Visual inspection: Examine mirror wiring, especially at the door hinge (flex points) and connectors for damage or corrosion.
4. Check connector fit: Unplug and re-seat connectors at the mirror and switch to rule out poor contacts.
5. Continuity test: Using a multimeter, verify continuity of the “down” circuit wire from switch to mirror motor.
6. Test mirror motor: Apply 12V directly to the motor’s down circuit to see if it responds.
7. Check switch function: Test the mirror switch’s down output with a wiring diagram and voltmeter.
8. Check fuses: Locate and test fuses associated with mirror controls.
9. BCM check: If all prior steps pass, consider a BCM fault; verify with OEM scan tool functions if available.

Possible Repairs for B1787 #

Restoring normal mirror function involves addressing the root cause of the open circuit. Depending on what the diagnosis reveals, repairs may include:

• Repairing or replacing broken/corroded wiring in the passenger mirror circuit
• Cleaning or replacing loose or oxidized connectors
• Replacing the passenger side mirror motor assembly
• Replacing a faulty mirror adjustment switch
• Repairing or, rarely, replacing the BCM (only if confirmed defective)
• Replacing any blown fuse related to the mirror control circuit

Is It Safe to Drive with Code B1787? #

Yes, you can continue driving with code B1787 active. This issue affects only the electrical adjustment of the passenger side mirror’s downward movement and does not impact basic vehicle safety, braking, steering, or engine performance. However, you may experience reduced convenience or visibility when parking or reversing. For vehicles with auto-tilt or memory mirrors, the feature may be unavailable until repairs are made.

Vehicles Most Commonly Affected by B1787 #

While B1787 is a generic Body DTC, it’s more frequently reported on models with advanced mirror systems or heavy use of electronic controls. The following types of vehicles are commonly affected:

• Toyota Camry, Avalon, and Lexus ES/GS (mid-2010s and newer)
• Honda Accord, CR-V, Acura TLX (late-2000s to present)
• Ford Fusion, Escape, Lincoln MKZ (2010+)
• General Motors (Chevrolet Malibu, GMC Acadia) with auto-tilt mirrors
• Hyundai Sonata, Kia Optima with memory or power mirrors

Common Mistakes & Best Practices for Code B1787 #

Misdiagnosis is common with mirror electrical issues, especially if symptoms overlap with other mirror faults. Here are mistakes to avoid and tips to get it right:

• Replacing the mirror motor before verifying wiring continuity
• Overlooking connector corrosion at the door or mirror plug
• Ignoring fuse checks, especially after recent electrical work
• Assuming BCM failure without prior step-by-step testing
• Always use a proper wiring diagram for your vehicle’s year/model
• Document any repairs or modifications made to the mirror circuits

Quick FAQ for Code B1787 #

Still have questions? Here are fast answers to the most common concerns:

• Q: Can a bad mirror switch cause B1787?
  A: Yes, a faulty switch can interrupt the “down” circuit, but always check wiring and connectors first.
• Q: Will clearing the code fix the problem?
  A: No, the code will return unless the open circuit is repaired. Clearing codes only resets the warning temporarily.
• Q: Does B1787 affect mirror heating or folding?
  A: No, this code specifically concerns the vertical “down” movement circuit. Other mirror functions remain unaffected unless otherwise faulty.