B1739: Driver Mirror Horizontal Switch High Voltage
Diagnostic trouble code B1739 indicates that the seat control module or body control module (BCM) has detected an abnormally high voltage on the driver's side mirror horizontal position switch circuit. This circuit includes the control switch located on the door or instrument panel, and the wiring that communicates the signal to the mirror adjustment motor. A 'short to battery' means the signal or control wire is receiving direct battery voltage instead of the expected reference signal, preventing proper horizontal mirror adjustment.
1. Commonly Affected Makes
2. Most Common Causes
- Damaged insulation on mirror switch wiring shorting to a battery power wire
- Driver mirror adjustment switch internally shorted
- Corroded, bent, or moisture-damaged pins in the switch or mirror motor connector
- Mirror motor with an open or internally shorted coil affecting the signal circuit
- Damaged output circuit in the driver seat module (DSM) or body control module (BCM)
3. Symptoms You Will Notice
- Driver side mirror does not adjust horizontally
- Mirror may move erratically or only in one direction
4. Step-by-Step Diagnosis
Check for technical service bulletins (TSBs) related to mirror or seat module issues
Inspect the mirror switch and motor connectors for corrosion, bent pins, or moisture
Test the mirror switch for internal shorts using a multimeter
Check the wiring between the switch and mirror motor for shorts to battery voltage
If wiring and switch are okay, test the mirror motor by applying battery voltage directly
If motor works, suspect a faulty DSM or BCM; perform module self-test or replace if necessary
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, the vehicle is safe to drive. The issue only affects the driver's mirror horizontal adjustment, which can be manually adjusted if needed.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on whether the fix involves cleaning connectors, replacing the switch ($50-$150), or replacing a module ($200-$400).