Code Definition

B1A85 (22) — Ambient Light Sensor Circuit – Signal Stuck Low

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

About B1A85

B1A85 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 B1A85 is stored, the module has detected a signal or supply voltage lower than the expected operating range; 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.

B1A85 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) reads a varying voltage from the ambient light sensor mounted at the top of the dash or moulded into the windscreen sensor cluster, and uses that input to control automatic headlamp activation, twilight delay, and dimming of the instrument cluster and dash illumination. Sub code 22 indicates a signal stuck low fault, meaning the BCM consistently sees a sensor voltage well below the expected daylight range regardless of actual ambient light, and the signal does not change over an extended monitoring period. The sensor is typically a photodiode or phototransistor th...

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