09 mack mp8

[Shandro]

Truck has just over 125000 miles doesn't get used all that much because we farm and it's used mostly in winter to haul grain to the elevator. The other day the intake manifold pressure sensor failed and was reading 40 pounds of boost. Ran the truck like that for 40 miles or so before it was derated and had to shut it off. Towed it home the rest of the way. Replaced the sensor and everything seemed great it regened and off I was hauling grain again. Two trips later code comes up for egr valve that it's either an open circuit or stuck wide open. Wires looked all good. What else could need cleaning/looking at besides the valve?