B2318

Mirror Passenger Vertical Feedback Potentiometer Circuit Short to Battery

Body Chassis/Safety Mirror Control 🟢 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 vertical position sensor is sending a constant maximum voltage signal to the ECU, like a stuck throttle pedal that won't report its actual position. This prevents the mirror from adjusting vertically or the system from knowing where it really is.

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Symptoms You May Notice

3 known symptoms for this code
Passenger mirror won't move up or down
Mirror control switch unresponsive in vertical direction
Warning light or fault message on dashboard
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors the potentiometer voltage output from the passenger mirror vertical actuator feedback circuit. It expects a variable voltage (0-5V) that changes as the mirror moves up and down. When the circuit shorts to battery voltage, the sensor constantly reads maximum voltage, preventing the ECU from detecting mirror position or movement commands.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Potentiometer Voltage 0.5V to 4.5V (variable with position) Stuck at 4.8V+ (shorted to battery)
Resistance Range 100Ω to 10kΩ (variable) < 50Ω or open circuit detected
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Wiring harness connector
Inspect and reseat the mirror control module connector at the door panel for corrosion or loose pins.
2
Mirror motor assembly
Replace the entire passenger mirror motor unit if internal potentiometer is shorted or damaged.
3
Mirror control module
Replace the integrated control module if wiring tests pass but fault persists.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B2318 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 B2318

What happens after you fix the fault

Once the fault is repaired, B2318 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.