I have had a EGR valve engine code on for quite some time now. PO402 EGR Flow Excessive Detected. I took it off and cleaned it with some carb cleaner. It was a bit dirty and the error did not go away until I replaced the cam position sensor. The EGR valve is on the back of the engine. Two bolts hold it on, but you have to clear the path from wires. Then the top removed with four screws. You can see all the carbon that was cleaned out from soaking it a couple of times and knocking it out.