B1784: Passenger Mirror Up Circuit Short to Battery
Diagnostic trouble code B1784 indicates a short to battery voltage (B+) in the passenger side mirror up circuit. This manufacturer-specific code is set when the body control module (BCM) or mirror control module detects abnormally high voltage on the mirror up actuator circuit while the electrical command is not active. The condition typically arises when the signal or return wire of the mirror motor makes direct contact with a 12-volt power source, often due to insulation breakdown in the door hinge wiring or an internal fault in the mirror assembly.
1. Commonly Affected Makes
2. Most Common Causes
- Short to battery (B+) in the passenger mirror up motor wiring
- Defective right mirror assembly (internal motor short)
- Damaged or chafed wiring within the door harness or hinge area
- Corroded or bent pins in the electrical connector causing a bridge to the power pin
- Faulty body control module (BCM) or mirror module (internal driver failure)
3. Symptoms You Will Notice
- Passenger side mirror does not adjust up or down
- Mirror may move erratically or only in one direction
- Blown fuse for the mirror circuit
- BCM may store additional related codes
4. Step-by-Step Diagnosis
Inspect the passenger mirror wiring harness at the door hinge for chafing or breaks
Check the mirror electrical connector for corrosion, bent pins, or signs of shorting
Disconnect the mirror and measure resistance between the up circuit and ground; a short to battery will show continuity to B+
Test the mirror motor by applying 12V directly to confirm operation
If wiring and mirror are good, suspect a faulty BCM or mirror module
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is generally safe to drive with code B1784. The issue is limited to the passenger mirror function and does not affect critical systems. However, the mirror may not adjust properly, and a short could potentially blow a 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 can run $200-$400 including labor.