The California Smog Check is a test of your vehicles emissions control systems
and an analysis of the tailpipe gasses. There are three parts to a California
Smog Check; visual, tailpipe emissions and functional. The vehicle must pass all
three parts of the test before it receives a Smog Certificate. If the vehicle
fails one or two of these parts of the test, all three will still be verified
during the re-test. The visual part of the Smog Check is to verify that all of
the smog related components are there and hooked up properly. If any parts are
missing, modified, disconnected, or defective the technician will enter this as
a fail. The passing of this part of the test does not mean that these parts are
functioning properly it only means they appear to be in the original condition.
The smog technician will not tell you if they see anything wrong with your
visual inspection until the test is complete as they are not allowed to. The
second part of the test is the emissions test. This part of the test checks the
vehicles emissions by parts per million or a percentage of the sample. If the
vehicles Hydrocarbons (HC), Carbon Monoxide (CO), or Nitrous Oxide (NO) levels
are over the maximum allowance the vehicle will fail. The test will also show
two other gasses; Carbon Dioxide (CO2) and Oxygen (O2), these gasses are used to
analyze and diagnose the vehicles performance, and the level of these gasses
will not cause the vehicle to fail. For the functional part of the smog check
the technician will physically test individual smog components to verify that
they operate properly. The type of Smog Check and the type of Vehicle will
determine which components will be functionally tested, if these components do
not function properly or are out of specification the technician will enter
fail. If all three of these tests pass the vehicle will be issued a Smog
Certificate.