B1740
Mirror Driver Horizontal Switch Circuit Short To Ground
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 switch is sending a constant ground signal to the ECU, like a stuck button that won't release. This short circuit prevents the mirror motor from responding to driver inputs.

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Symptoms You May Notice
3 known symptoms for this code
Driver-side mirror won't adjust horizontally left or right
Mirror control switch unresponsive or stuck in one position
Fault code stored in body control module
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors the voltage signal from the horizontal mirror switch circuit. Normally the switch creates variable resistance; when shorted to ground, voltage remains near 0V continuously. The ECU detects this abnormal low voltage condition as a fault.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Switch circuit voltage 0.5V to 4.5V (variable with switch position) Below 0.2V (continuous ground short)
Circuit resistance 500Ω to 5kΩ (variable) Below 100Ω (short condition)
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Mirror switch connector
Inspect and reseat the electrical connector at the mirror switch for corrosion or loose pins.
2
Mirror switch assembly
Replace the faulty horizontal switch control module in the door panel.
3
Wiring harness
Repair or replace damaged wiring in the mirror control circuit that may be shorted to vehicle ground.