Hello I just purchased a 1996 e320 with 124,000 miles and there is a code po400 the mechanic told me dont worry about it?? Is that true?if not how will this cost to get fixed? Also my gas gauge sometimes will show empty when i start the car up and i know i have alot of gas in it, can someone help my with this problem. Also my driver side headlamp bulb went out can someone tells us how to replace it ourselves? I am a newbie with some questions. The car didn't come with the manual. So i am asking for help. One last thing should we purchase the obd2 code reader so we will know about codes? Thanks for all the help and support.