Mirror Driver Horizontal Switch Circuit Short To Ground
The mirror's horizontal adjustment switch is sending a constant ground signal to the ECU, like a stuck button that won't release. This short circuit prevents the mirror motor from responding to driver inputs.
The ECU monitors the voltage signal from the horizontal mirror switch circuit. Normally the switch creates variable resistance; when shorted to ground, voltage remains near 0V continuously. The ECU detects this abnormal low voltage condition as a fault.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Switch circuit voltage | 0.5V to 4.5V (variable with switch position) | Below 0.2V (continuous ground short) |
| Circuit resistance | 500Ω to 5kΩ (variable) | Below 100Ω (short condition) |
Code B1740 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, B1740 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.