Answer:
When the D light is blinking, an error in the transmission sensor or control system has been detected. It can ramge from a loose sensor wire to a failing trans.
You would need to retrieve the trouble code to understand what is causing the problem. Autozone provides free scanning services. Get the exact trouble code and we can proceed with diagnostics.
If there is no abnormal noise or gear shifting irregularities, it is safe to drive the vehicle. If light goes off after restarting and would only come on later, it would normally be caused by a malfunctining sensor. If the speedometer is not working, it can cause the light to illuminate.
