Will aftermarket headers cause my car to fail the smog test?
Unless the aftermarket headers you purchase and install have an EO stamp, meaning they have been tested by the California Air Resource Board and been issued an Executive Order number, yes they will fail the smog inspection; as a tampered emission component. Exhaust headers, not to mention the entire AIR Air injection system is an "emissions component". Any modification to the headers, intake manifold, or exhaust manifold, including removal of a "Y" tube from the exhaust pipes (if equipped) is considered an emissions tamper. Your vehicle will fail the smog inspection even before the tailpipe exhaust is checked.
Mufflers: The smog test does not test the muffler. However we don't recommend you take the vehicle in for testing if your vehicle's muffler is broken or has holes in it from damage or rust. It may cause the smog technician problems getting the smog machine to accept testing your vehicle.
Smog machines are calibrated in California every three days, and are designed to not allow the testing of vehicles which emit oxygen levels exceeding a smog machines preset limits. In other words, if your vehicle's muffler has large holes which are allowing oxygen to be vacuumed in with the emissions stream, the test results would have been inaccurate. The smog machine may not allow the inspection to continue and/or fail the smog inspection.
California Smog Check Program applies to the following vehicles - A smog certificate will be required to operate these vehicles on public roadways: Acura, Alfa Romeo, Aston Martin, Audi, BMW, Bentley, Buick, Cadillac, Chevrolet, Chrysler, Lamborghini, Daihatsu, Dodge, Eagle, Ferrari, Ford, GMC, Geo, Honda, Hummer, Hyundai, Infiniti, International, Isuzu, Jaguar, Jeep, Kia, Daewoo, Land Rover, Lexus, Lincoln, Lotus, Maserati, Maybach, Mazda, Mercedes Benz, Mercury, Mini, Mitsubishi, Morgan, Nissan, Oldsmobile, Peugeot, Plymouth, Pontiac, Porsche, Rolls-Royce, Saab, Saturn, Scion, Smart, Sterling, Subaru, Suzuki, Toyota, Volkswagen, VW, Volvo.