What does it mean when the D4 light is flashing on a Honda Prelude?

The D4 light flashing on a Honda Prelude indicates a problem with the vehicle's Dual Stage VTEC (Variable Timing and Valve Lift Electronic Control) system. The VTEC system is responsible for controlling the timing of the engine's valves, and when it malfunctions, it can cause a variety of problems, including reduced engine power, rough idling, and stalling. If the D4 light is flashing, it is important to have the vehicle diagnosed by a qualified mechanic as soon as possible.