Went into limp or safe mode checked for codes P2149 has me worried !

What is your question?

Changed the fuel filter noticed crud at base of housing so i drained diesel and used a scotch pad to remove the scale! Also used towels to lift the noticeable dirt etc. reset the computer and turned off CEL check engine light and erased codes! First trial run was ok however im not sure if i fixed the problem as it also mentioned that Group B injectors may have an open circuit on the supply side? Is the supply side the "high" side? Can i check it without taking off the valve cover? Again it was a P2149 code