October 19, 2017

What is a Gross Polluter vehicle?

The Smog Check program has identified Gross Polluter (GP) vehicles as a significant source of smog emissions. Gross Polluter vehicles are chosen through these strategies:

  • Vehicles tested at licensed stations which exceed at least one of the gross polluter standards (twice the maximum emission limits)
  • Vehicles selected from the High Emitter Profile (HEP) database which have a high probability of failing the Smog Check inspection.

Once a vehicle is classified or designated as a Gross Polluter it has to initially be tested at a Test Only inspection station. If the vehicle fails this inspection it must undergo repairs and return to a Test only center, State Referee station or a Gold Shield CAP (Consumer Assistance Program) repair center for certification.

Vehicles, which are not classified, as gross polluters, do not have to seek a Test Only inspection and can visit any local smog station. Your DMV paperwork or documents will indicate which type of test your car or vehicle requires.

It is estimated that 50% of the smog in the state of California is produced by motor vehicles. Gross Polluters represent only approximately 10 to 15 percent of all these vehicles, however they are estimated to be responsible for more than half of all vehicle smog emissions.


Gross Polluters pollute much more than a the typical vehicle that fails a Smog Check inspection. The emission level at which a vehicle fails as a Gross Polluter varies according the vehicle type and year. Typically they exceed at least one of the gross polluter standards (twice the maximum emission limits).

Older vehicles are not held to the same emissions standards as newer vehicles. Older vehicles were built to less stringent standards when originally manufactured and thus the smog inspection process is developed with this in mind. The vehicle owner of an older vehicle is given a slight handicap or advantage. They must however up keep their vehicle’s maintenance to at least par.

Excessive Smoke: Gross Polluting vehicles will often produce excessive white or black smoke from the tailpipe. This should be a clear indication that your vehicle’s engine is in trouble.

Typically a vehicle emitting excessive white or black smoke will be designated as a gross polluter after the smog inspection. It is highly recommend you seek repair assistance prior to getting a smog check or emission test.

Black Smoke: Excessive black smoke from the muffler is almost always due to a rich fuel mixture and will produce high CO, and consequently high HC during the smog check or inspection.

White Smoke: A vehicle emitting excessive white smoke from the tailpipe may have a burned or blown head gasket. A blown head gasket may cause overheating and high NOx emissions. Most often the level of NOx produced will be twice the allowed limit, rendering your vehicle as a gross polluter or HEP.