Beginning July 19, 2021, Californian automotive enthusiasts have yet another item to add to an ever-expanding list of dos and don'ts (mostly don'ts) regarding their mandatory biennial visits to certified smog facilities. Up to this point, if your car was armed with modified programming (software) on its ECU (Engine Control Unit), and as long as you passed a smog test, no one would raise an eyebrow. Come Monday, however, if your car's ECU program isn't verified as legal by a California Air Resources Board (C.A.R.B.) Executive Order, then your car won't pass smog, regardless of its emissions output.
It might seem like common sense given the Golden State's reputation for strict smog guidelines and astronomical fees that only seem to increase each year, but again, previously, countless vehicles roamed California's roads with performance-minded tunes applied to their ECUs. So long as the engine ran clean enough to meet state emissions guidelines, the smog tech would have no issue passing you. As of the 19th, if detected, an ECU modified in any way from the original factory settings without a C.A.R.B E.O. will result in your not getting an oh-so-vital piece of the vehicle registration puzzle.
For those using a system like Hondata's FlashPro, a unit that plugs directly into the vehicle's OBD II diagnostic port and allows custom calibration of fuel, timing, and other parameters, as well as real-time and stored data-logging options, returning the ECU to factory settings is quick and painless. Hondata even offers a slightly less potent C.A.R.B.-compliant version of the plug-in (CARB EO D-742-1) which, as mentioned earlier, is just fine by California officials.