B1421 is a code used to identify a particular type of engine fault on some Honda vehicles. The code indicates that there is an issue with the engine's camshaft position sensor. This sensor is responsible for monitoring the position of the camshaft and sending a signal to the vehicle's computer. When this sensor fails, it can cause the engine to run improperly or stall completely. In some cases, it may also trigger the check engine light. Replacing the faulty sensor should fix the problem and clear the code.