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Will aftermarket ECU tune fail my BMW smog?

Yes — under the post-July 2021 rule.

Per BAR diagnostic standards + CARB rulings.

This entry also has a full Q&A treatment: smoganswers.com/q/will-aftermarket-ecu-tune-fail-my-bmw-smog/

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Last reviewed 2026-05-25 · Cal Smog Network canonical answer library