My son has a 2002 Dodge 2500 Diesel has codes P0522 and P0336. The oil pressure switch, which is a single wire switch, has been replaced with a Cummins part and the PO336 code is troubling because there is no crank shaft sensor on a 2002. When you start the truck the instrument cluster shows no oil pressure and the tach is erratic for 8 seconds then drops off and the truck runs at a normal RPM but is in limp mode. ANY help would be appreciated.