B1739
Mirror Driver Horizontal Switch Circuit Short To Battery
Body Chassis/Safety Mirror Control Circuit 🟢 Low — Fix at next service
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What This Actually Means
In plain language — no jargon

The mirror's horizontal adjustment motor circuit is shorted directly to battery power, preventing the ECU from controlling the mirror position. It's like a light switch stuck in the ON position due to a wire touching the power line.

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Symptoms You May Notice
3 known symptoms for this code
Driver side mirror won't adjust horizontally or moves uncontrollably
Mirror control switch becomes unresponsive or inoperative
Possible burning smell or electrical buzzing from mirror assembly
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors voltage levels on the mirror motor control circuit, expecting variable resistance based on switch input. When the circuit shorts to battery voltage (typically 12-14V), the ECU detects abnormally high voltage at the control pin, indicating a direct short rather than normal PWM control signals.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Mirror Motor Control Voltage 0-5V PWM signal or variable 0-12V Sustained 12-14V (battery voltage)
Circuit Resistance Varies with switch position < 1 ohm (direct short to battery)
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Wiring harness connector
Disconnect and inspect the mirror control connector for corroded pins or damaged wires touching positive battery supply.
2
Mirror motor assembly
Replace the driver side mirror motor if internal wiring is shorted to the motor housing or power line.
3
Mirror control switch
Replace the dashboard mirror control switch if internal contacts are fused or shorted to battery power.