Ok, you have CA emissions.
Basically the code is set because the glow plug feed back voltage does not match what the ecm is looking for, I would imagine something is wrong because it takes two consecutive failures to turn on the light. If your feedback voltage is between 5 and 6 volts, your ok, if its less then 3 volts, you have one or more glow plugs giving fits. It wont give you much grief while the weather is warm, but once winter hits, it could be trouble, might better get it checked out before then.. A couple quick checks you could do is to make sure the power connection to the glow plug controller is tight, the controller is mounted on the drivers side valve cover at the back of the engine....