as.thompson

This from the CA Bureau of Automotive Repairs:Beginning July 19, 2021, vehicles with software not provided by the original equipment manufacturer (OEM) or approved through a California Air Resources Board (CARB) Executive Order (EO) will fail Smog Check.Before your vehicle will pass a Smog Check, you must have the vehicle’s software restored to the OEM software version. Once the software is restored, have your vehicle reinspected by a licensed Smog Check station. Note that vehicles initially directed to a STAR or Referee station must return to the same station type to complete the inspection process.If you believe the vehicle’s software is already OEM or CARB-approved and yet your vehicle failed Smog Check, schedule an inspection with the Smog Check Referee.If you unknowingly purchased a vehicle with illegally-modified software, you may file a complaint with BAR.

E55Greasemonkey

And how will they know what software it has???

superswiss

They don't need to specifically know which software it has, but they can check file names and compare checksums. Tuners have a habit of naming the files differently from the OEM files, so that will raise a red flag, and they can very easily scan the memory, calculate the checksum and compare it to the OEM checksum, based on data submitted from the manufacturers. There is the potential of false positives if the OEM updates the ECU software, but the checksum information hasn't made it to the SMOG testers yet, but it's very easy to tell if an ECU has been flashed with different software by just adding up the bytes and see if you get the expected checksum.