Land Rover B109c-15 -

The most overlooked step. A poor ground (earth) point at the rear chassis (G4D21 or similar) will cause the BCM to see a floating voltage. Measure resistance from the lamp ground pin to the chassis. It should be less than 1 ohm.

With the turn signal activated (hazard lights on), use a multimeter at the connector: land rover b109c-15

. In the Land Rover diagnostic architecture, the "-15" suffix specifically denotes a general electrical failure characterized by a circuit short to battery or an open circuit Technical Breakdown of DTC B109C-15 Description : Front Courtesy Lamps. Failure Sub-type (-15) : Circuit short to battery or open. Controlling Module : This code is often logged by the Passenger Door Module (PDM) Body Control Module (BCM) , which manages interior lighting. Common Symptoms Interior Lighting Malfunction The most overlooked step

Do not panic. Perform the swap test first. If the fault moves, you simply need a new lamp. If it doesn't, check your battery and your grounds. In the worst case, a dealer software update will silence the gremlin. It should be less than 1 ohm

For many owners, this code triggers a wave of confusion. Is it a minor glitch or a sign of imminent electronic failure? What does "B109C-15" actually mean, and how much will it cost to fix?

If your Land Rover is 3+ years old and you have random electrical gremlins (B109C-15 plus "Low Battery" warnings), replace the main AGM battery. You must reset the Battery Monitoring System (BMS) using a scanner after replacement.

Unlike a simple "bulb out" code (which is usually a Type 02), the B109C-15 suggests a more complex electrical anomaly that the BCM cannot rectify.