1996 Pontiac Grand Am Question: abs sensor oil senser struts

mechanic said i needed front pasenger side s wheel sensor i installed sensor but light stays on the codes he put down werent four ditgits but regardless asumming he was correct why would the light stay on. oil pressure light has been coming on for seven months but car has no problem driving. i can make it go off temperarily by pumping pedal first. I got stryt plates replaced but still get crunchingsounds