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.
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.