A large source of smog on this planet comes from vaporized hydrocarbons that are released from the fuel system and engine of vehicles as they drive down the road. The largest source of this is unburned fuel that works its way into the exhaust, or fuel vapor that escapes the fuel tank. This is where the evaporative emissions system comes into play. Instead of venting fuel vapor into the atmosphere as the standard once was, it is now collected in a canister and burned off through the combustion process. The 2004 RX-8 has a different type of engine compared to most cars on the road, but the emissions system remains virtually the same as on any other vehicle built after 1996.
Code P0456 means the powertrain control module detected a very small leak in the EVAP emissions system. This is commonly caused by a loose or damaged gas cap.
