What Does B1739 Mean?
This code indicates that the Body Control Module (BCM) has detected an abnormal voltage condition in the driver's side mirror horizontal adjustment switch circuit. Specifically, the circuit is shorted to battery voltage, meaning voltage is present when it should not be, or higher voltage than expected is detected on the switch signal wire. This prevents proper horizontal mirror adjustment control on the driver's side.
Common Causes
40%
Damaged or pinched wiring harness between BCM and driver's mirror switch causing direct contact with battery voltage
30%
Faulty driver's side mirror control switch with internal short to power circuit
20%
Water intrusion or corrosion in mirror switch connector causing cross-circuit short
10%
Failed Body Control Module (BCM) with internal circuit fault causing false short detection
Diagnostic Steps
1
Step 1: Perform visual inspection of the driver's side mirror control switch and surrounding door panel area for signs of liquid intrusion, physical damage, or recent repairs that may have pinched wiring
2
Step 2: Disconnect the driver's side mirror control switch connector and use a digital multimeter to measure voltage on the horizontal switch signal wire at the harness side (BCM side) with ignition on - should read 0-0.5V with switch disconnected; battery voltage confirms wiring harness short
3
Step 3: If no voltage found at harness, reconnect switch and backprobe the horizontal switch circuit while operating the switch - voltage should toggle between ground and reference voltage (typically 5V); continuous battery voltage indicates faulty switch
4
Step 4: Inspect the wiring harness routing from door jamb through door panel to mirror switch for pinch points, chafing against metal edges, or damage from window regulator mechanism using visual and tactile inspection
5
Step 5: If all wiring and switch test normal, check BCM connector terminals for corrosion, pushed-back pins, or damage that could cause internal module fault detection
6
Step 6: Clear codes, operate mirror switch through full range of motion, and verify code does not return - if code immediately returns with known-good components, BCM replacement may be required
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
This code indicates that the Body Control Module (BCM) has detected an abnormal voltage condition in the driver's side mirror horizontal adjustment switch circuit. Specifically, the circuit is shorted to battery voltage, meaning voltage is present when it should not be, or higher voltage than expect...
The most common cause of B1739 (Mirror Driver Horizontal Switch Circuit Short To Battery) is: Damaged or pinched wiring harness between BCM and driver's mirror switch causing direct contact with battery voltage
Typical repair costs for B1739 range from $100 to $600, 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 and does not impact vehicle operation or safety systems. Repair at convenience, though proper mirror adjustment is important for visibility and safe lane changes.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1739 to identify the root cause.
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Quick Info
Category
Body
System
Body Control and Convenience Systems
Difficulty
Type
Manufacturer
Recommended Tools
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