Here's what I found on the DMV website:

"In order for your vehicle to receive a Smog Check certificate, it must pass all the following elements:

A visual inspection, in which all required emissions control components and systems are identified, and must appear connected and functional.

A functional inspection, which includes checking the operation of the emissions control warning indicators, ("Check Engine" light), the ignition timing, the gas cap, and the Exhaust Gas Recirculation (EGR) system (if the vehicle is so equipped and a Two-Speed Idle (TSI) test is being performed). A functional check of a vehicleÆs On-Board Diagnostic (OBD) system is also performed on 1996 and newer vehicles. Diagnostic information stored in the vehicleÆs computer is reported on the Vehicle Inspection Report (VIR) that the motorist receives at the end of the Smog Check inspection. OBD information can save time and money when repairs are required.

A tailpipe emissions test, which measures exhaust emissions using a probe inserted into the vehicleÆs tailpipe during testing. Vehicles pass or fail this part of the Smog Check inspection based on established emission standards, sometimes called cutpoints."


It also says that the seller is required to provide the certificate to the seller!