Mirror Passenger Down Circuit Open
The passenger side mirror's down control circuit has a broken electrical connection, like a light switch with a severed wire that can't complete the circuit. The mirror motor won't respond when you try to move it downward.
The ECU monitors the voltage and current flow through the passenger mirror down circuit when the switch is activated. It expects to see a complete circuit with proper voltage drop across the mirror motor. If no current flows or voltage remains high, the ECU detects an open circuit fault.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Mirror Down Circuit Current | 0.5-3.0 amps when activated | No current or below 0.1 amps |
| Circuit Voltage Drop | Below 2 volts across motor | Above 10 volts or battery voltage |
Code B1787 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.
Once the fault is repaired, B1787 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.