B1734 — Mirror Driver Vertical Switch Circuit Open #

Note: The wording of this Diagnostic Trouble Code (DTC) may vary depending on the vehicle manufacturer.

• Mirror Driver Vertical Switch Circuit Open (Generic/OEMs)
• Driver Mirror Vertical Adjustment Switch Open Circuit (Ford, GM)
• Power Mirror Vertical Switch Open (Honda, Nissan)
• Left Mirror Up/Down Switch Circuit Open (Toyota, FCA/Chrysler)

Summary of DTC B1734 #

DTC B1734 is an OBD-II body code indicating an open circuit in the vertical adjustment switch for the driver-side power mirror. In simpler terms, the vehicle’s computer has detected that the electrical path controlling the up-and-down movement of the driver’s mirror is broken or interrupted. This malfunction prevents the mirror from being adjusted vertically from the control switch inside the cabin. The code is typically set when the Body Control Module (BCM) or Door Control Module (DCM) senses an abnormal voltage or lack of continuity in the switch circuit during a self-check or when the switch is operated. While not threatening to vehicle safety, it can affect comfort and driver visibility.

Common Symptoms for DTC B1734 #

When B1734 is present, you’ll likely notice issues related to the power adjustment of the driver-side mirror. The most obvious symptom is the inability to move the mirror vertically using the internal switch. Occasionally, this malfunction may coincide with other power mirror issues or warning lights. Here’s what you might observe:

• Driver-side mirror does not move up or down when using the adjustment switch
• Mirror may only move horizontally (left/right), not vertically (up/down)
• No response or sound from the mirror motor during vertical adjustment
• Possible warning message or indicator on the instrument cluster (on some models)
• No effect on other vehicle systems or driveability

Probable Causes for DTC B1734 #

Several factors could trigger the B1734 code, most involving the electrical path between the mirror switch, the mirror motor, and the control module. The most common causes, ranked by frequency, are:

1. Faulty driver mirror vertical adjustment switch — physical wear or internal failure
2. Open or broken wiring between the switch and the mirror motor
3. Corroded, loose, or damaged electrical connectors at the switch or mirror
4. Faulty mirror motor (vertical adjustment circuit)
5. Blown fuse or relay supplying power to the mirror circuit
6. Internal fault in the Body Control Module (BCM) or Door Control Module (rare)

Step-by-Step Diagnostic for DTC B1734 #

Proper diagnosis avoids guesswork and ensures you address the root cause. Here’s a recommended process:

• Visual inspection: Check the switch, mirror, and harness for obvious damage or corrosion.
• Use a scan tool to confirm code B1734 and check for other related mirror or body codes.
• Test mirror operation to verify if only vertical adjustment is affected.
• Check for power and ground at the mirror switch using a multimeter.
• Backprobe the switch output while activating the vertical adjustment — look for continuity.
• Inspect and test the wiring harness from the switch to the mirror and to the control module.
• Test the vertical adjustment motor at the mirror for function; apply 12V directly if possible.
• If all wiring and components check out, consider module diagnostics or reprogramming (rare).

Possible Repairs for DTC B1734 #

The repair will depend on which component or section of the circuit is faulty. Based on the most common causes, consider the following:

• Replace the driver mirror vertical adjustment switch if faulty
• Repair or replace damaged wiring or connectors between the switch, mirror, and control module
• Clean or secure corroded connectors
• Replace the mirror motor if the vertical circuit is open or nonfunctional
• Replace blown fuse or faulty relay supplying the mirror circuit
• In rare cases, reprogram or replace the BCM/DCM after confirming all other components are good

Can You Drive with DTC B1734? #

Yes, you can continue driving safely with code B1734 present. This issue only affects the vertical adjustment of the driver’s power mirror; it does not impact vital vehicle systems or safety features. However, if the mirror is locked in a position that compromises your rearward view, it’s wise to adjust it manually (if possible) before driving. Address the issue soon to restore full convenience and visibility.

Vehicles Most Commonly Affected by DTC B1734 #

B1734 is most frequently seen on vehicles equipped with power mirrors and advanced body electronics. The following manufacturers and models are known to use this code or similar wording:

• Ford (Focus, F-150, Fusion, Escape)
• Chevrolet/GMC (Silverado, Malibu, Equinox)
• Toyota (Camry, Corolla, RAV4)
• Nissan (Altima, Rogue, Sentra)
• Honda (Accord, Civic, CR-V)
• Chrysler/Dodge/Jeep (Ram, Grand Cherokee, Charger)

Other OEMs with power mirror systems and OBD-II/EOBD architecture may also report this code.

Common Mistakes & Best Practices for DTC B1734 #

Misdiagnosis can waste time and money. Here are the frequent pitfalls and how to avoid them:

• Replacing the mirror motor or switch without testing the wiring — always check for open circuits first.
• Overlooking corrosion or loose connectors, especially in door areas exposed to moisture.
• Ignoring simple fixes like a blown fuse or relay before replacing expensive parts.
• Not using a wiring diagram to trace the circuit — guessing leads to repeat failures.
• Failing to clear the code after a repair, so the code may reappear unnecessarily.

Express FAQ for DTC B1734 #

Still have questions? Here are quick answers to common concerns:

• Q: Can I manually adjust my driver’s mirror if B1734 is active?
  A: In most modern vehicles, the manual override is limited. If possible, you can try adjusting the glass by hand, but take care not to force or break the mechanism.
• Q: Will fixing B1734 require reprogramming any modules?
  A: Rarely. Most repairs involve hardware (switch, wiring, motor). Module reprogramming is only needed if a confirmed internal fault exists after all other components test good.