MY JETTA BATTERY ISNT HOLDING CHARGE IT KEEPS DRAINING, HELP!!!!

MY JETTA ISNT HOLDING CHARGE. I BOUGHT A NEW BATTERY AND A NEW ALTERNATOR THINKIN THAT WAS THE PROBLEM, WELL I TOOK IT TO AUTOZONE AND THEY PUT THE SCAN ON IT, AND IT CAME BACK WITH TWO CODES, 1.THE CPS CRANK POSITIONING SENSOR 2.BAD ELECTRIAL PROBLEM, HOW SHOULD I CHECK IT OR HOW SHOULD I LOOK FOR THE MAIN PROBLEM, HELP!! SHOULD I REPLACE THE SENSOR?