B1789

Mirror Passenger Down Circuit Short To Ground

Body Chassis/Safety Mirror Control Circuit 🟢 Low — Fix at next service ✅ Safe to Drive
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What This Actually Means

In plain language — no jargon

The passenger side mirror's down control circuit is shorted to ground, meaning electricity is taking a shortcut instead of flowing properly through the mirror motor. It's like a light switch where the wire is touching the metal frame, so the circuit can't work correctly.

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Symptoms You May Notice

3 known symptoms for this code
Passenger mirror down button unresponsive or inoperative
Mirror control module warning light illuminated on dashboard
Possible electrical burning smell near door panel
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The body control module monitors the voltage and current in the passenger mirror down circuit. It expects a specific resistance range when the button is pressed; a short to ground causes abnormally low or zero resistance, triggering the fault code.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Circuit Resistance 50-500 ohms during operation Less than 10 ohms or zero ohms
Circuit Voltage 10-14 volts when active 0-2 volts or continuous ground
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Door panel harness connector
Disconnect and inspect the mirror wiring connector for corrosion, water damage, or bent pins; clean or reseat as needed.
2
Mirror control wiring
Check the down-circuit wire for pinching, abrasion, or insulation damage between the door panel and mirror motor.
3
Passenger mirror motor assembly
Replace the mirror motor if internal windings are shorted or if connector pins are corroded beyond cleaning.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1789 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
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How to Clear Code B1789

What happens after you fix the fault

Once the fault is repaired, B1789 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.