Code Definition

B1791 — Autolamp Sensor Input Circuit Open

System: Body  |  Type: Manufacturer-Specific  |  Make: Ford

About B1791

B1791 is a manufacturer-specific body diagnostic trouble code recorded for Ford vehicles. It belongs to the B-prefix family of codes, which covers body, interior, airbag, or comfort-electronics faults.

When B1791 is stored, the module has detected an open (broken or disconnected) electrical path in the monitored circuit; and a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: Body (B) codes are often stored in the body control module, airbag module, or climate module. A basic OBD-II tool usually will not read body codes — an enhanced or OEM-level scan tool is typically required.

B1791 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The Body Control Module (BCM) monitors the autolamp sensor input circuit so that the exterior lighting can be controlled automatically based on ambient light. The autolamp sensor is a photocell typically mounted on top of the dashboard under a translucent dome that returns a variable voltage to the BCM as the light level changes. DTC B1791 is set when the BCM detects an open circuit on the autolamp sensor input, meaning the signal voltage has either gone to zero with no return current or has stayed pinned at the reference voltage with no load. When this code is set, the autolamp feature will n...

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