Engine-Codes - Generic - B1791

B1791 Code - Autolamp Sensor Input Circuit Open

- Code Popularity: 8,442 Views
- Repair Importance Level: 3/3
- Repair Difficulty Level: 3/3
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What are the Possible Causes of the DTC B1791?

NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
  • Faulty Light Sensor
  • Light Sensor harness is open or shorted
  • Light Sensor circuit poor electrical connection
  • Faulty Headlamp Switch
  • Faulty Smart Junction Box (SJB)
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How to Fix the DTC B1791?

Check the 'Possible Causes' listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.

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What is the Cost to Diagnose the Code?

Labor: 1.0

The cost to diagnose the B1791 code is 1.0 hour of labor. The diagnosis time and labor rates at auto repair shops vary depending on the location, make and model of the vehicle, and even the engine type. Most auto repair shops charge between $75 and $150 per hour.

What are Code Possible Symptoms?

  • Engine Light ON (or Service Engine Soon Warning Light)

What Does the B1791 Code Mean?

The Smart Junction Box (SJB) sends a voltage signal to the headlamp switch and the light sensor.
When the headlamp switch is placed in the AUTOLAMPS ON position, the voltage signal is routed to ground. When the SJB detects the headlamp switch in the AUTOLAMPS ON position, the SJB monitors the light sensor input. The light sensor determines the amount of light based on the input received from the ambient lighting conditions. When the ambient level has reached a point (determined by the internal programming of the SJB ), the SJB provides voltage to the headlamps, parking and license plate lamps. The Diagnostic Trouble Code (DTC) sets when the SJB detects an open from the light sensor input circuit.

B1791 Code - Autolamp Sensor Input Circuit Open

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Code B1791 Information for Specific Makes

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