OBD Guide
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B1791

Autolamp Sensor Input Circuit Open

B1791 is an OBD-II diagnostic trouble code meaning: Autolamp Sensor Input Circuit Open. Common causes: broken wires in the harness, oxidation of sensor contacts. Estimated repair cost: $33–111.

Severity
✅ Low
Can you drive?
Limited driving only, diagnose soon
Approx. repair cost
$33–111 (est.)

Symptoms

  • Automatic lighting does not turn on
  • Headlights do not respond to changes in light conditions
  • The malfunction indicator on the dashboard is on

Causes

  • Broken wires in the harness
  • Oxidation of sensor contacts
  • Auto light sensor malfunction
  • Blown fuse
  • Problems with the lighting control unit

How to Fix

  1. Check the condition of the wiring harness for breaks
  2. Clean the sensor contacts from oxidation
  3. Check sensor circuit fuse
  4. Test automatic light sensor
  5. Check the operation of the lighting control unit

Related codes

B1790B1792

FAQ

What does the B1791 code mean?

B1791 is an OBD-II diagnostic trouble code that indicates: Autolamp Sensor Input Circuit Open

What causes a B1791 error code?

The most common causes of B1791 include: Broken wires in the harness; Oxidation of sensor contacts; Auto light sensor malfunction; Blown fuse.

How do I fix a B1791 diagnostic trouble code?

To fix B1791: Check the condition of the wiring harness for breaks. Clean the sensor contacts from oxidation. Check sensor circuit fuse. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with B1791?

Limited driving only, diagnose soon

How much does it cost to fix B1791?

The estimated repair cost for B1791 is $33–111. Actual cost depends on your vehicle, location, and labor rates.

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