2001 4.4i engine light on.

[ausx5]

Hey guys, I haven't posted here before so here goes.

I recently bought an E53 4.4i sport and am in the slow (and suprisingly expensive) process of fixing it's inherrant X5 problems.

I was driving home the other night and the engine light appeared on the dash. During that day the temperature got up to 45 degrees (celcius), which is pretty warm here in Aus! So the next day i checked the coolant level and it was very low and was not even registering on the level indicator, although the temp guage didn't even flicker the day before. I guessed that the engine light was on possibly to warn me of this, so i topped up the coolant level this afternoon but the engine light is still on. Is this possibly because:-
a) The light will reset once car goes into it's 'sleep mode' overnight
b) I need to get the light reset by someone
c) There is a separate issue all together, meaning the light will stay on untill i resolve what ever the other problem may be! (i'm thinking this one myself!)

Any help here would be much appreciated. As i said i'm new here and my mechanical knowledge especially with BMW's isn't great.

Thanks in advance,

Ben.