The passages for the Exhaust Gas Recirculation (EGR) system can become restricted or clogged causing the Check Engine Light to illuminate. The EGR valve will need to be inspected and the passages cleaned.Google+
Car Problem Reports
Mazda Protege Check Engine Light Due to Restricted EGR System
Mazda Protege Problem
Average Mileage: 102,500 mi (86,500 mi - 118,500 mi)
Didn't need to be replaced. Pulled it out and cleaned the inside. Check engine light has not come back on since. I have gone about 4000 miles since then and still good.
Visitor, 2003 Mazda Protege, 86,500 mi
REPAIR EGR VALVE 0N 2003 MAZDA PROTEGE