The P2003 engine code is a kind of powertrain problem and it is easy to solve. The catalytic converter has an oxygen sensor behind and in front it. When the automobile is hot and running in locked loop mode, the upstream oxygen sensor waveform reading should alter. When you see the car engine code P2003 or the fault code on your engine code reader this explanation will help you. The controllers of each cylinder are reserved closed using a pair of arms that replace the conservative engine’s roller-type rocker arm. The engine code P2003 is one of these arms what follows the cam profile while the 2nd arm connects to the valves.