ECU monitors transaxle operation. ECU contains a self-diagnostic system which stores a fault code if a transaxle electronic control system failure or problem exists. If a fault code is stored, ECU will turn on and blink "D4" light on instrument panel.
Mine did this right before my speedometer went out.If the speedo goes soon it is your speed sensor. I had this problem and found a speed sensor repair kit online. The kit cost $75.00 plus labor was much cheaper than a new speed sensor.