B1640: Left Mirror Circuit Open
The B1640 code indicates that the control module has detected an open circuit in the left passenger side mirror. This means the module cannot send or receive the necessary electrical signals through the mirror's control, power, or ground circuits, disabling functions such as power adjustment, heating, or perimeter lighting. The fault is often due to wiring fatigue in the door-to-body harness, corroded connectors, or internal failure of the mirror actuator or heating element.
1. Commonly Affected Makes
2. Most Common Causes
- Broken, disconnected, or fatigued wiring in the harness between the door and A-pillar
- Corroded, oxidized, or retracted pins in the left mirror connector
- Open internal circuit in the mirror adjustment motor or heating resistor
- Loose, corroded, or missing ground point for the mirror circuit
- Blown fuse for the mirror circuit (if applicable per vehicle wiring)
3. Symptoms You Will Notice
- Left mirror does not adjust electrically
- Left mirror heating or turn signal (if equipped) inoperative
4. Step-by-Step Diagnosis
Inspect the door-to-body wiring harness for breaks or chafing, especially near the hinge area.
Check the mirror connector for corrosion, bent or pushed-back pins.
Test for power and ground at the mirror connector using a multimeter.
If power and ground are present, test the mirror actuator and heater resistance; replace if open.
Verify the mirror circuit fuse is intact and replace if blown.
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is safe to drive. The fault only affects the left mirror's electrical functions; manual adjustment is still possible, and safety is not compromised.
How much does it cost to fix?▼
Repair costs range from $50 to $200 for wiring or connector repairs, and $150 to $400 for mirror assembly replacement, including labor.