1994 Acura Legend Drive 4 light flashing then park light tu

While driving, the temperature gauge goes to "H"ot then back down to the midpoint level but car never overheats and coolant is not leaking or disappearing from the coolant container. The thermostat and radiator cap have been replaced. Also the green box around the "D4" (Drive gear) flashes once the car heats up to normal temps. At the same time the red box around the "P" (parking) remains on while being driven. This occurs at normal speed limits. Your assistance is greatly appreciated.