2006 Saturn Vue what does P0378 as a code mean

2006 Saturn Vue 4 cyl Front Wheel Drive Automatic

The check engine light in my wife's view has been going on and off intermittently for the past couple weeks.

Last night, the car wouldnt start at all, but it would turn over but the engine wouldnt catch.

This morning, the battery was totally dead. I jumped it and it ran fine, including being shut off and restarted.

I had a friend who works on his own cars check the battery, the alternator, and the starter, and all were fine.

He hooked up a code scanner and the only code shown was P0378, so my question is, what does it mean, and what do I need to do about it? I know it said something abou the timing, but dont know what would need to be fixed to correct it.

Also, what would have caused the battery to go dead because of the error?

thanks