Code Definition

B109B — Licence Plate Lamp Circuit Fault

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

About B109B

B109B 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 B109B is stored, the module has detected an electrical-circuit fault in the wiring, connector, or driver associated with the named component.

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.

B109B 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) controls the licence plate lamps through a low side driver output and continuously monitors the circuit for correct electrical behaviour. Code B109B sets when the BCM detects an open circuit (no current flow when the lamps are commanded on), a short to ground, or a short to battery voltage for longer than the calibration threshold. The circuit is typically fused from the BCM and routed through a body or tailgate grommet to the licence plate lamp housings at the rear of the vehicle. When this code is active the licence plate lamps may fail to illuminate, a lamp out...

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