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  • Writer's pictureJustin Turner

Will a tune pass California smog tests?

As of July 19, 2021, California's notoriously strict smog testing will automatically fail any car when it detects modified software onboard, aka, a tuned ECU. Drivers can't register a car in the state unless it's passed a smog check.

All is not lost for those driving a modified car in need of a smog check, though. The state government says drivers can simply restore the ECU to the OEM standard, pass the smog test and then do whatever they'd like after that. One thing to note is that California smog testing will still have zero issues with cars running ECU tunes with a California Air Resources Board Executive Order. These EO tunes receive approval from CARB, so companies can still sell their tuning services in the state without any emissions repercussions. If you're running an EO ECU tune, there's no need to worry about this new policy at all. Downside here is that CARB certification is VERY expensive and most tuning companies are unlikely to attempt the process.

One other thing to note is that CA also requires a CVN check. A CVN is a "Calibration Verification Number." This is the number that is calculated and reported by the engine system to validate the calibration/software integrity. When you flash tune an ECU it changes the CVN significantly. Many tunes can pass basic smog with no issue, but it's this CVN check that can get your vehicle flagged.

YotaWerx cannot guarantee passing of a smog test and CVN check. As a customer, you bear the risk of this modification and its potential effects on vehicle emissions testing results. As a customer running a YW tune (or planning to), you have a couple of options:

Option A: Have your tuner flash you back to stock so you can pass smog, then re-flash the tune you paid for. Most (if not all) tuners would have no issue doing this)

Option B (DIY): Buy vF Tuner flash kit ($399), administer the flash back to stock (vF Tuner provides stock files for all supported ECU ID's), then re-flash your tune (Note: you will need a cpy of the actual tune file from your provider).

Additional info can be found here:

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