Passenger Mirror Up Circuit Short to Ground
Code B1785 indicates a short to ground in the passenger side mirror up circuit, specific to Toyota/Lexus vehicles. This code is triggered when the mirror control module (master switch assembly or mirror ECU) detects an abnormally low voltage signal on the control circuit for the passenger mirror's upward tilt motor. The system monitors resistance and voltage of the stepper or DC motors that control mirror movement; a short to ground prevents proper upward movement and can damage the control module if left uncorrected.
1. Commonly Affected Makes
2. Most Common Causes
- Short to ground in the passenger mirror up circuit wiring
- Internal insulation failure in the passenger mirror motor
- Moisture or corrosion in the passenger mirror connector causing a short
- Internal failure of the mirror control module (master switch assembly)
- Wiring harness chafed or damaged due to friction in the passenger door
3. Symptoms You Will Notice
- Passenger side mirror does not move upward
- Mirror may move in other directions but not up
4. Step-by-Step Diagnosis
Inspect the passenger mirror wiring harness for damage, especially where it passes through the door hinge area.
Check the passenger mirror connector for moisture, corrosion, or bent pins.
Test the mirror motor by applying direct power and ground to verify operation.
Measure resistance between the mirror up control wire and ground; a low reading indicates a short.
If wiring and motor are good, suspect a faulty mirror control module.
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is generally safe to drive, but the passenger mirror will not adjust upward, which may reduce visibility. The underlying short could potentially damage the control module over time, so repair is recommended.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on whether the issue is a simple wiring repair or requires replacement of the mirror assembly or control module.