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Some folks on social media have started to post about a new California smog testing procedure that is supposed to check for modified or non-CARB compliant software in vehicle ECUs, which I did some digging into. Using the link posted at the bottom of the screenshots I’ve seen, I followed it back to the California Bureau of Automotive Repair’s smog FAQ page, where the confirmation was clear as day: California is indeed going to start sniffing for tunes during smog checks.

California Will Start Checking for ECU Tuning In Smog Checks This Month
Here’s the relevant excerpt from the above-linked FAQ page. Image: BAR.ca.gov screenshot

As many of you may know: Cars need to pass a smog check for emissions compliance every other year if they want to be registered in California. It’s pretty much the only legal requirement to keep your car on the road here, but inspectors can be real hardasses about modifications even if they don’t really make your car’s pollution any worse.

Beginning July 19, 2021 (next week!), vehicles will be checked for modified software of any kind and fail smog if it’s found. This marks a small but significant change in smog testing procedures which, previously, was not this invasive. Smog checks in California usually consist of a thorough visual inspection to make sure your intake and exhaust system are legal, and an emissions readiness check via a scan of the OBD2 port. 

I’ve personally never run a tuned car through a smog check, and I was going to chance it with the Stage One APR tune on my GTI based on anecdotal evidence from other tuned car owners. Now, I’m nervous to try (though my tune is supposed to be legal, we’ll get into that below). I can only guess the mechanisms by which smog referees are checking for tunes, but it should be pretty simple. You can check for software very easily through the standard OBD2 port that every post-1996 car has, and I’m sure all that will be done is an extra software inspection of the ECU during the smog check. 

Tunes basically work like normal computer files, and tuners also love to leave signatures behind that are telltale signs of modification being done. For example, the APR tune file on my car is pretty blatantly called “VW GTI NA MY2010 2.0T CBFA 1K0907115AL S0030 Stage 1+ V2.5 APR Intake [APR Mobile],” which will definitely set off some alarm bells to anybody looking for non-standard files. Smog referees don’t need to even to performance-test the car, they can now just see if the files have been changed.

These files, and the tables within them, tell the ECU what to do and what targets to hit. I will also hazard a guess that the smog referee or smog machine doesn’t actually sniff the ECU files for modification, rather just checking for a changed file name. It would be impossible for them to check every single fueling, ignition, and airflow table in the ECU, of which there are dozens. So maybe those of us who have what’s called a “pro tune,” or a custom tune done on a dyno, could potentially get past it with a tuner willing to keep the file name stock-looking.

After I did some Googling based on an email tip I got, it seems that the easiest way to check for software changes could be through something called a CVN (Calibration Verification Number). The number is actually a checksum — something that the ECU adds up from each segment of memory. Basically, when you change software or coding, the sum of the numbers in the memory segments changes, which changes the total checksum. This makes it easy to spot mistakes or changes in text or code, and CARB will apparently use this as a known profile to check individual cars against, thanks to automakers submitting data or years of data collection via smog checks. This piece on Alt Car News seems to indicate that will happen; this old forum post from EFI Live explains the checksum idea a little more.

There are various checksums in a car’s computer, but this could be a prime candidate for the state’s methods of smog inspection because the OEMs decide the number that it should add up to, and the data could be made available to the state.

This has some caveats, however. The CVN can change with updates or with different options on a given car. Some ECUs have a locked CVN or are totally encrypted. This info is only increasing my feeling that this new smog check will increase false positives and cause headaches to car owners in general. As far as CARB-certified tunes, I’d imagine that the CVNs from those tunes are or will be submitted to CARB and flagged as valid for smog.

Either way, the state believes that tunes constitute an emissions control system tamper. This means consumers are exempt from assistance from the state until the car is returned to its factory state of tune. So quite a few kids buying random turbo cars might get a rude awakening when the car had a tune that they didn’t know about.

The lack of official release and announcement as of writing this is also telling; the state wants to nab anybody who tunes their car before they realize it’s being checked. Tuned car owners officially have less than a week to sneak a smog check-in, but some smog stations are already deploying the new checks before the official date of July 19. 

This one feels like a big bummer to me, but I knew the risk was always there. It’ll be an extra couple hundred bucks every two years, but I’m going to have to start flashing my car back to stock, smogging it, then reinstalling the tune. Clean air is a noble goal, and I respect it. But for those of us who retain factory emissions hardware and catalytic converters, the increase in emissions from a flash tune is negligible. Sure, go after the dudes who run catless downpipes and burble tunes that pointlessly waste fuel to sound grumbly, which I suspect are the catalyst to this hasty action. There are plenty of people like myself looking for some extra power without hurting anybody. I want to keep my car clean and low-key, but now I get to waste some extra money every two years.

My APR tune is actually CARB compliant and should be able to pass smog legally. The next question will be if I can pass cleanly, or will I have a headache based on the inspection method adopted by the state? APR didn’t have much to say about the new checks, but Arin Ahnell, Brand Manager at APR contributed this statement: “Our goal is emissions compliance on all of our products. We don’t support any methods to circumvent compliance. We actively seek a CARB EO on our software, and have it on many tunes already.”

The old checks were just fine at catching egregious modifications that actually hurt the sonic and emissions environment of a given city. Now, we have another layer of checks to weed out everybody. A respectable endeavor, sure. But we’re doing all of this while the state approves more fracking permits? I’m afraid this feels like a method to stop the burble tune madness that ballooned into killing one of the fundamental mods of any car.

The good news is that the state hasn’t said that getting the tune is illegal, but there are rumblings of shops getting fined by the EPA for defeating emissions devices. We’ll see how this develops here, and for now, tuners are officially put on notice.

Update 07/13/21: This post has been updated to include the explanation of how smog inspectors could check for software changes through CVNs, clarify that the author’s APR tune is CARB legal, and add the statement from APR’s representative.


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