What Does B1738 Mean?
This code indicates the Body Control Module (BCM) has detected an open circuit in the driver's side power mirror horizontal adjustment switch circuit. The BCM monitors the switch inputs for the left/right movement of the driver's mirror and has detected a break in electrical continuity, preventing horizontal mirror adjustment commands from being received. This is a manufacturer-specific body code related to the power mirror control system.
Common Causes
45%
Failed or damaged mirror adjustment switch assembly with internal open circuit or broken contacts
30%
Broken or corroded wiring between the mirror switch and BCM, including damaged connectors or terminals
15%
Loose or corroded electrical connector at the mirror switch or BCM causing intermittent or complete loss of continuity
10%
Failed Body Control Module with internal circuit fault in the mirror switch input circuit
Diagnostic Steps
1
Step 1: Visually inspect the driver's door mirror switch assembly for physical damage, broken tabs, or signs of water intrusion. Test the switch operation manually to verify horizontal adjustment function while monitoring for tactile feedback and resistance.
2
Step 2: Using a digital multimeter, check for continuity across the horizontal switch circuit terminals with the switch in neutral, left, and right positions. Expected readings should show open circuit in neutral and closed circuit (near 0 ohms) when actuated in either direction.
3
Step 3: Disconnect the mirror switch connector and inspect terminals for corrosion, bent pins, or spread female terminals. Check voltage supply to the switch (typically 5V or 12V reference) and ground circuit integrity using a multimeter.
4
Step 4: Perform a continuity test on the wiring harness between the mirror switch connector and the BCM connector with both ends disconnected. Wiggle the harness through the door jamb area while testing to identify intermittent opens caused by flexing damage.
5
Step 5: If all wiring and connections test good, substitute a known-good mirror switch assembly and retest. If fault persists, inspect BCM connector terminals and consider BCM circuit board diagnosis or replacement.
6
Step 6: Clear codes, cycle the mirror adjustment through all positions multiple times, and road test to verify repair. Monitor for code recurrence using live data to confirm switch signal reception at the BCM.
Estimated Repair Cost
$75 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected an open circuit in the driver's side power mirror horizontal adjustment switch circuit. The BCM monitors the switch inputs for the left/right movement of the driver's mirror and has detected a break in electrical continuity, preventing h...
The most common cause of B1738 (Mirror Driver Horizontal Switch Circuit Open) is: Failed or damaged mirror adjustment switch assembly with internal open circuit or broken contacts
Typical repair costs for B1738 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 driver's side mirror horizontal adjustment convenience feature. This does not impact vehicle operation or safety systems, though proper mirror adjustment is important for visibility and should be repaired when convenient.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1738 to identify the root cause.
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Quick Info
Category
Body
System
Body Electrical System - Power Mirror Controls
Difficulty
Type
Manufacturer
Recommended Tools
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