Mirror Driver Down Circuit Failure
The driver-side mirror's down motor circuit isn't working properly, similar to a broken remote control that can't send signals to lower the mirror. The ECU detects an electrical failure in the circuit that powers the mirror down movement.
The ECU monitors voltage and current draw through the mirror down circuit during actuation commands. It compares motor feedback signals against expected resistance patterns and current thresholds to detect shorts, opens, or motor failures.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Circuit Current Draw | 2-5 amps during down operation | 0 amps (open circuit) or >8 amps (short circuit) |
| Motor Response Time | Movement detected within 500ms | No movement signal after 1 second of command |
Code B1778 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, B1778 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.