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ECU-tuned cars will now automatically flunk California smog testing

However, the state still says you're free to flash an ECU to stock and return the tune after the test.

CA smog check

Smog checks aren't anything new in CA, but this rule change is something to be aware of.

Barry Lewis/Getty Images

Here's a good reminder to anyone running a tuned car out in California: As of today, July 19, the state'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. Car Bibles first spotted the updated policy and the California Bureau of Automotive Repair confirms the changes on its website.

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. As long as your car won't puke its guts out running a stock map, drivers should be all right. This is, more than anything, a good reminder of the policy change.

In addition, 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. In addition, the policy doesn't change anything regarding vehicles from the 1975 model year and older. They still don't need a smog check for registration in the state. Cars nine years or older than their sale date still require a smog check every other year.