B1738
Mirror Driver Horizontal Switch Circuit Open
Body Chassis/Safety Mirror Control 🟢 Low — Fix at next service
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What This Actually Means
In plain language — no jargon

The side mirror's horizontal adjustment motor circuit has lost electrical connection, like a broken wire in a lamp cord. The mirror won't move left or right when you try to adjust it.

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Symptoms You May Notice
3 known symptoms for this code
Driver side mirror won't move horizontally left or right
Mirror adjustment buttons produce no response or clicking sound
Warning light or message appears on dashboard related to mirror function
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors voltage and current flow through the mirror motor's horizontal adjustment circuit. It expects continuity and proper voltage when the adjustment switch is activated, detecting an open circuit when resistance becomes infinite or voltage drop is abnormal.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Circuit Resistance Less than 5 ohms Greater than 100 ohms or open circuit
Motor Voltage 10-14V when activated 0V or no change detected
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Wiring harness connector at mirror
Disconnect and reconnect the mirror electrical connector to clean any corrosion causing the open circuit.
2
Wiring and connectors between switch and motor
Visually inspect the wire routing behind the door panel for pinches, cuts, or loose connections and repair or reseat as needed.
3
Mirror motor assembly
If wiring is intact, replace the entire mirror motor unit as the internal circuit is likely broken.