OBD Guide
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B123F

Automatic Lighting Control Unit/Sensor Internal Error

B123F is an OBD-II diagnostic trouble code meaning: Automatic Lighting Control Unit/Sensor Internal Error. Common causes: malfunction of the automatic lighting control unit, light sensor damage. Estimated repair cost: $56–167.

Severity
⚠️ Medium
Can you drive?
Limited driving only, diagnose soon
Approx. repair cost
$56–167 (est.)

Symptoms

  • Incorrect operation of automatic lighting
  • Headlights do not turn on/off automatically
  • Flashing headlights or other lighting fixtures
  • Error message on the dashboard

Causes

  • Malfunction of the automatic lighting control unit
  • Light sensor damage
  • Problems with wiring harness or contacts
  • Failures in the control unit software

How to Fix

  1. Check the condition of the light sensor and its connection
  2. Check the wiring harness for damage or corrosion.
  3. Scan the control unit for additional errors
  4. Reflash or replace the automatic lighting control unit if necessary

Related codes

B123EB1240U0121

FAQ

What does the B123F code mean?

B123F is an OBD-II diagnostic trouble code that indicates: Automatic Lighting Control Unit/Sensor Internal Error

What causes a B123F error code?

The most common causes of B123F include: Malfunction of the automatic lighting control unit; Light sensor damage; Problems with wiring harness or contacts; Failures in the control unit software.

How do I fix a B123F diagnostic trouble code?

To fix B123F: Check the condition of the light sensor and its connection. Check the wiring harness for damage or corrosion.. Scan the control unit for additional errors. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with B123F?

Limited driving only, diagnose soon

How much does it cost to fix B123F?

The estimated repair cost for B123F is $56–167. Actual cost depends on your vehicle, location, and labor rates.

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