what is code P1391

That code is for the crankshaft position sensor or the CMP sensor which goes under the distributor cap for instructions on how to test these sensors go to sinautoscan.com under forum also i would get this check soon because once the CKP sensor goes your car wont start at all.

If this happens under heavy load, such as when going uphill, the likely suspect is a cracked flexplate. The camshaft position sensor takes its reading from the pulse windows in the flexplate rim. Under the load, the outer part of the flywheel moves relative to the center, causing the code to set. I am dealing with this problem right now and have a hard time convincing my trusted shop to investigate in that direction. I may end up having to drop the transaxle myself.