There can be many causes of EGR faults, depending on make, model, and fuel type. If the EGR valve can be removed, you may have success cleaning it with Berryman B-12 Chemtool Carburetor, Choke & Throttle Body Cleaner (part #0117/0117C). Ultimately, though, the exhaust need to be cleaned up for a long-term fix. This is often accomplished with detergent-based cleaners, such as B-12 Chemtool Total Fuel System Clean-Up (part #2616) for gasoline or Berryman Diesel Injector Cleaner (part #0518) for diesel.