This test is in addition to the tailpipe emissions test. The smog technician will be required to enter his/her observation into the smog machine after the emissions test portion of the smog check.
Excessive smoke, either black or white will cause a smog check failure. If your vehicle is emitting visible smoke, you will need to have the fault diagnosed and repaired before it can pass the smog check. Vehicles with severe engine damage may be emitting smoke from the engine compartment. This too will cause a visible smoke test failure.
What causes excessive black smoke? Visible black smoke may indicate one of two things.
1. The engine is not burning fuel properly, leaving behind high amounts of Carbon Monoxide (CO), resulting in excessive black smoke being emitted from the tailpipe. These vehicles will experience increased fuel consumption as well.
2. Engine oil is seeping into the combustion chambers. Oil is mixing with the fuel & air mixture, leaving behind high amounts of carbon, seen as excessive black smoke being emitted from the tailpipe. Oil seepage may occur due to defective piston rings, valve seals, or Positive Crank Ventilation (PCV) System.
What causes excessive white smoke: Visible white smoke may indicate a burned or blown head gasket. Excessive white smoke (steam) is caused by water seepage into the combustion chambers, which on a running engine, operate around 2500f. Water has an opportunity to enter the combustion chambers through the head gasket, at the junction of an engine's valve head and block. This will typically cause overheating and white smoke in the exhaust coming out of your car's tailpipe.
Note: Excessive white smoke should not be mistaken with normally emitted white smoke typically seen during cold days, and until an engine is properly warmed up. The smog check program is aware that vehicles may emit white smoke when cold, and ensures a vehicle is properly warmed up prior to administering the smog test.
White smoke during startup or in cold weather is simply steam, and will not cause a smog check failure.