Passenger Mirror Down Circuit Failure
The B1786 code indicates that the Body Control Module (BCM) or Driver Door Module (DDM) has detected a fault in the passenger side mirror's 'Down' control circuit. This typically points to an open circuit, short to ground or battery in the wiring that powers the mirror's vertical motor, or an internal failure of the mirror motor or control module.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty passenger side mirror motor (internal open circuit in the 'Down' winding)
- Damaged, corroded, or shorted wiring between the door module (DDM/PDM) and the mirror
- Loose, bent, or corroded pins in the mirror or door module connector
- Internal failure of the Driver Door Module (DDM) or Passenger Door Module (PDM)
- Blown fuse for the power mirror circuit
3. Symptoms You Will Notice
- Passenger side mirror does not move downward
- Mirror may not respond to any adjustment commands
- Possible intermittent mirror operation
4. Step-by-Step Diagnosis
Check the power mirror fuse and replace if blown
Inspect the mirror and door module connectors for damage, corrosion, or loose pins
Test the mirror motor by applying direct power and ground to the 'Down' circuit
Check for continuity and shorts in the wiring between the door module and mirror
If wiring and motor are good, suspect a faulty DDM or PDM
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is safe to drive. The fault only affects the passenger mirror's downward adjustment, which is a convenience feature and does not impact vehicle safety.
How much does it cost to fix?▼
Repair costs typically range from $50 to $300, depending on whether the issue is a blown fuse, wiring repair, or replacement of the mirror assembly or door module.