What Does B1734 Mean?
This code indicates that the Body Control Module (BCM) has detected an open circuit in the driver's side mirror vertical adjustment switch. The BCM monitors the switch inputs that control up/down movement of the driver's side power mirror and has detected a break in the electrical circuit, preventing proper mirror adjustment. This is a manufacturer-specific body control code related to the power mirror adjustment system.
Common Causes
45%
Faulty driver's door master mirror switch assembly with internal open circuit or broken contacts
30%
Broken or damaged wiring harness between mirror switch and BCM, particularly in door jamb flex area
15%
Corroded or loose connector terminals at mirror switch or BCM connection points
10%
Failed Body Control Module (BCM) with internal circuit board damage affecting mirror switch input monitoring
Diagnostic Steps
1
Step 1: Perform visual inspection of driver's door mirror switch panel for physical damage, water intrusion, or obvious defects. Check mirror switch operation manually to confirm vertical adjustment does not function.
2
Step 2: Remove door panel and inspect wiring harness in door jamb area for breaks, chafing, or damage from repeated door opening/closing. Wiggle harness while monitoring for intermittent connection.
3
Step 3: Using a digital multimeter, backprobe the mirror switch connector at the vertical switch terminals. With ignition on, test for proper voltage supply (typically 5V or 12V reference) and verify continuity through switch when actuated up/down.
4
Step 4: If switch has proper voltage supply but no continuity when actuated, replace mirror switch assembly. If no voltage present, trace circuit back to BCM connector and test for open circuit in harness using wiring diagram.
5
Step 5: Inspect BCM connector terminals for corrosion, bent pins, or poor contact. Clean connections with electrical contact cleaner and apply dielectric grease.
6
Step 6: After repair, clear codes, cycle mirror switch through all positions multiple times, and verify code does not return. Test mirror vertical adjustment functionality to confirm proper operation.
Estimated Repair Cost
$75 - $450
Parts + labor, varies by vehicle and location
This code indicates that the Body Control Module (BCM) has detected an open circuit in the driver's side mirror vertical adjustment switch. The BCM monitors the switch inputs that control up/down movement of the driver's side power mirror and has detected a break in the electrical circuit, preventin...
The most common cause of B1734 (Mirror Driver Vertical Switch Circuit Open) is: Faulty driver's door master mirror switch assembly with internal open circuit or broken contacts
Typical repair costs for B1734 range from $75 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving as this only affects mirror adjustment convenience feature. Repair is not urgent but should be addressed for proper mirror positioning and visibility optimization.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1734 to identify the root cause.
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Quick Info
Category
Body
System
Body Control/Power Accessories
Difficulty
Type
Manufacturer
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