Code Definition

B1C39 (29-28) — Key Locking Switch – Signal Invalid or Signal Bias Level Out of Range

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

About B1C39

B1C39 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 B1C39 is stored, the module has detected a plausibility fault — the measured value is in the electrical range but is not consistent with expected operating behaviour.

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.

B1C39 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 key locking switch input that reports the mechanical lock cylinder position from the ignition or steering column lock assembly. This switch tells the BCM when the key has been turned to lock, off, accessory, or run positions, allowing the BCM to coordinate functions such as steering column lock release, illuminated entry, anti theft arming, and key in ignition warnings. DTC B1C39 with sub code 29 (Signal Invalid) or 28 (Signal Bias Level Out of Range) is set when the BCM detects that the signal from the key locking switch is electrically inconsistent,...

Join TaT to view the complete code information and diagnostic details.

Quick Facts