B1646: Right Mirror Circuit Short to Ground
Diagnostic trouble code B1646 indicates a short to ground in the passenger side mirror circuit, specific to Honda/Acura vehicles. The mirror control module detects abnormally low resistance or a direct ground connection in the power or control circuit of the right exterior mirror, preventing normal operation and potentially causing the fuse to blow. The system continuously monitors circuit integrity when the ignition is on or the power mirror adjustment is activated.
1. Commonly Affected Makes
2. Most Common Causes
- Damaged or chafed wiring in the right mirror circuit contacting chassis ground
- Corroded or bent pins in the mirror connector causing a short circuit
- Internal short to ground in the right mirror adjustment motor coil
- Faulty mirror control module (MICU/Body Control Module)
- Passenger door harness damaged by friction or water intrusion
- Improper aftermarket modification or installation affecting the mirror circuit
3. Symptoms You Will Notice
- Passenger side mirror does not adjust electrically
- Blown fuse for the mirror circuit
- Mirror may move erratically or not at all
4. Step-by-Step Diagnosis
Inspect the passenger door harness for chafing, cuts, or water damage, especially near the door hinge area.
Check the mirror connector for corrosion, bent pins, or signs of shorting.
Measure resistance between the mirror control circuit and ground; a reading near zero ohms confirms a short.
Disconnect the mirror and test the motor windings for internal short to ground.
If wiring and mirror are good, test the mirror control module (MICU) for internal failure.
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is generally safe to drive, but the passenger mirror will not function electrically. However, if the short causes a fuse to blow repeatedly, it may affect other circuits on the same fuse.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on the cause. A simple wiring repair may cost $100-$200, while replacing the mirror assembly or control module can run $200-$400.