B1789 — Mirror Passenger Down Circuit Short To Ground #

Note: The exact wording of this Diagnostic Trouble Code (DTC) may differ between manufacturers. Always refer to your vehicle’s service manual for OEM-specific descriptions.

• B1789 — Mirror Passenger Down Circuit Short To Ground (Toyota, Lexus)
• B1789 — Power Mirror (RH) Down Circuit Short to Ground (Honda)
• B1789 — Passenger Side Mirror Down Switch Circuit Low (Generic/Others)

Summary of Code B1789 #

Code B1789 is an OBD-II Body (B) code that signals an electrical problem in the passenger (right-side) power mirror down circuit. Specifically, it means the mirror’s “down” function circuit is shorted to ground, which prevents normal operation. This code is commonly detected by the vehicle’s Body Control Module (BCM) or Mirror Control Module, depending on the OEM design. Although not critical for vehicle operation, this fault can affect mirror adjustments, reducing safety and comfort for the passenger or driver. Ignoring this code may also mask other electrical issues within the mirror system.

Common Symptoms for Code B1789 #

When B1789 is active, drivers usually notice problems with the passenger-side power mirror’s movement. The most apparent symptom is the inability to move the mirror downward using the control switch. Sometimes, related electrical symptoms may manifest, such as blown fuses or unusual noises from the mirror motor. In rare cases, the mirror may move erratically or become unresponsive altogether.

• Passenger-side mirror does not move downward when using the switch
• Other mirror directions (up, left, right) may still work
• Possible clicking or buzzing noise from inside the mirror housing
• Mirror moves down by itself or erratically
• Blown mirror control fuse
• Error message or warning light on the dashboard (vehicle dependent)

Probable Causes for Code B1789 #

B1789 is most often caused by electrical faults related to wiring or components in the passenger-side mirror down circuit. The issue may stem from a damaged harness, corroded connectors, or a failed switch. Less commonly, the mirror motor itself or the BCM/mirror control module may be at fault. Prioritize checking the most common causes before moving to more complex diagnostics.

1. Short to ground in the mirror down circuit wiring (most common)
2. Damaged or corroded connector at the mirror or door harness
3. Faulty mirror control switch (driver or passenger side, depending on design)
4. Defective power mirror motor (passenger side)
5. Internal fault in the BCM or dedicated mirror control module (rare)
6. Incorrectly installed aftermarket accessories tapping into mirror wiring

Step-by-Step Diagnosis for B1789 #

Accurate diagnosis of B1789 involves a systematic approach to locate the source of the short to ground. Use an OEM wiring diagram and a quality digital multimeter (DMM). Always disconnect the battery before probing connector pins to prevent accidental short circuits. Here’s a tried-and-true diagnostic path:

1. Verify the DTC: Scan for B1789 and any related codes (e.g., other mirror or door module faults).
2. Inspect the mirror’s physical operation—does it move in all directions except down?
3. Remove the passenger mirror glass and cover for visual inspection of the wiring and connector.
4. Check for broken, pinched, or corroded wires in the mirror harness and door-to-body boot (flexible rubber conduit).
5. Test the mirror down circuit for continuity to ground using a DMM with the mirror switch in all positions.
6. Disconnect the mirror and control switch connectors; check for shorts between the down circuit and ground at both ends.
7. Test the mirror control switch for proper function and resistance values as per OEM specs.
8. If no faults found, inspect the BCM or mirror control module for proper power and ground, and check for internal faults using advanced scan tools.

Possible Repairs for Code B1789 #

Once the root cause of B1789 is identified, repairs should address the faulty component or wiring section. Always clear the code and retest the system after any repair. Here are common solutions matched to the primary causes:

• Repair or replace damaged wiring: Splice and insulate wires that are pinched or shorted to ground.
• Clean or replace corroded connectors at the mirror or door harness.
• Replace the power mirror control switch if it fails resistance or continuity tests.
• Install a new passenger-side mirror motor if it’s internally shorted.
• Reprogram or replace the BCM or mirror control module if diagnosed as defective (rare).
• Remove or correctly rewire any aftermarket equipment interfering with the mirror circuit.

Is It Safe to Drive With Code B1789? #

Yes, it is generally safe to drive with code B1789 present. This code does not affect core vehicle functions like steering, braking, or engine performance. However, proper mirror adjustment is essential for visibility and safety—especially before changing lanes or parking. If the passenger mirror is stuck in an unsafe position, adjust it manually or get the issue resolved promptly to maintain optimal visibility.

Vehicles Most Commonly Affected by B1789 #

B1789 is most frequently reported on Japanese and some Korean vehicles equipped with power-adjustable mirrors, especially those from the late 1990s onward. Toyota and Lexus models are the most common, but Honda, Hyundai, and other brands may also use this code or a similar variant.

• Toyota Camry, Corolla, RAV4, Highlander
• Lexus RX, ES, IS series
• Honda Accord, Civic, CR-V (certain years)
• Hyundai Sonata, Elantra, Santa Fe (selected models)
• Other makes/models with power mirror systems (less common)

Common Mistakes & Best Practices for B1789 #

Misdiagnosis of B1789 often results from skipping basic wiring checks or overlooking connector corrosion. It’s tempting to replace the mirror or switch first, but this can lead to unnecessary parts costs. Always follow a logical diagnostic process with OEM diagrams and specifications to avoid wasted time and money.

• Mistake: Replacing the mirror assembly before inspecting the wiring or switch.
• Mistake: Ignoring connector corrosion in the door harness or mirror plug.
• Mistake: Overlooking aftermarket wiring modifications or alarm installations.
• Best practice: Use OEM wiring diagrams and a DMM to test circuits before replacing components.
• Best practice: Always clear codes and confirm full function after any repair.

Quick FAQ for Code B1789 #

Q: Will B1789 cause my power mirrors to stop working completely?
A: Not necessarily. B1789 typically affects only the “down” movement on the passenger-side mirror. Other directions may still work unless there are additional faults.

Q: Can I adjust the affected mirror manually if the motor doesn’t work?
A: In most cases, yes. Carefully tilt the mirror glass by hand if it’s safe to do so. Do not force it—some designs may be damaged by manual adjustment.

If you have any doubts or if the code reappears after repairs, consult an experienced technician with access to OEM wiring diagrams and diagnostic tools. Proper troubleshooting ensures safe driving and preserves the function of your vehicle’s power mirror systems.