my car was doing that for a while after some runs. it'd go away and come back everyonce in a while. i thought that too much spraying finally killed my tranny and made it throw some codes. some people told me it was my TCM but it was actually because i hooked up my n2o pressure guage power through a relay fuse and the wiring was loose or something and eventually causing that fuse blew and then the symptons of a flashing d4 came back but the d4 wasnt blinking because all the lights, guages, sunroof, clock, power windows were dead. couldnt even get out of park unless i shut down the car, stuck the key in the little shifter release lock and put it in neutral and started the car. check your fuses and the speed sensor also like everyone else said.