My check engine was on and I i went to a mechanic and he said that it was the EGR Flow sensor(I think that is what he said). He said he reset the codes and drove it around the block and he said that the light didnt come back on so it should be fine. Well now the light is on. I really cant afford a 500 dollar job could anyone tell me how much the part should be and does it need to be fixed right away?