Do you know what the #1 reason is that cars don’t pass their smog check? According to Diamond Certified smog check experts, a “check engine” / “service engine soon” light ON and/or high tail pipe emissions are the main reasons. The state sets the maximum allowed limits for hydrocarbons, carbon monoxide, oxides of nitrogen, referred to as “NOX”. A worn out catalytic converter can also be one of the many causes for not passing.
Each smog check station has its own policy as to whether they charge you for a failure. The state does not regulate that. In general, shops set their own prices for all smog checks, other than the state regulated $8.25 for the Smog Certificate. If your car fails the smog test close to the registration deadline, you may ask DMV for an extension to make failed smog related repairs.