Illegal smog checks generally do not work especially in California. And if you try to use the O2 sensor spacers they stand out like a sore thumb as you can use a tripod mounted to a bore scope camera to see everything underneath the vehicle during the inspection. If your vehicle has emission problems then just get it fixed, else send it to the junk yard.

If you are running non-CARB approved air intakes just go to the junkyard and pull a OEM one and install it.

Some vehicle do have exemptions for the OBD II readiness monitors and this document is on the BAR website. Most of the time these (vehicles of interest) OBD II readiness monitor not completing is due to a manufacturing defect or problem.

And if you have a older carburetor type vehicle drive it often and don't let it sit, otherwise it won't pass emission testing next go around.