2006 Subaru Impreza Owner's Manual - Page 230

If at any time you suspect that exhaust fumes are entering the vehicle, have the problem checked and corrected as soon as possible. If you must drive under these conditions, drive only with all windows fully open. Keep the trunk lid (Sedan) or rear gate (Wagon) closed while driving to prevent exhaust gas from entering the vehicle. Catalytic converter Driving tips 8-3 The catalytic converter is installed in the exhaust system. It serves as catalyst to reduce HC, CO and NOx in exhaust gases, thus providing cleaner exhaust. To avoid damage to the catalytic converter: Use only unleaded fuel. Even a small amount of leaded fuel will damage the catalytic converter. Never start the engine by pushing or pulling the vehicle. Avoid racing the engine. Never turn off the ignition switch while the vehicle is moving. Keep your engine tuned-up. If you feel the engine running rough (misfiring, backfiring or incomplete combustion), have your vehicle checked and repaired by an authorized SUBARU dealer. Do not apply undercoating or rust prevention treatment to the heat shield of catalytic converter and the exhaust system. Avoid fire hazards. Do not drive or park the vehicle anywhere near flammable materials (e.g. grass, paper, rags or leaves), because the catalytic converter operates at very high temperatures. – CONTINUED – NOTE Due to the expansion and contraction of the metals used in the manufacture of the exhaust system, you may hear a crackling sound coming from the exhaust system for a short time after the engine has been shut off. This sound is normal. Turbo models 800232 Non-turbo models 800218