Cat C7 starts and dies, code 15

Good Morning! I have a 2002 Tiffin Phaeton with a C7 Cat engine with around 62K miles, it ran great when put away last fall but a few days ago when I was getting it ready for a weekend trip the batteries were dead, I charged them up and it fired up and idled for a little bit then the check engine light came on and it died, now it will start idle a bit sputter and die. I'm getting a 15 code which means " open or short circuit of injection actuation pressure sensor". I'm wondering if anyone else has dealt with this problem and also any tips to access the engine area? I assume its under the floor between the bed and rear closet.