Aftermarket tuners: what to look up before a smog check

Aftermarket Tuners and Smog Check Research

Quick answer: BAR's Smog Check Manual lists tuners, chips, modules, PROMs, pods and other devices that change engine computer inputs or outputs as parts inspectors check for a CARB EO, and BAR's inspection includes a modified software check. Research whether your tuner and the software it loaded have a CARB EO covering your vehicle, or whether the vehicle is running factory software.

What BAR says

Appendix C of the Smog Check Manual covers "variable or alternate tuning devices," including anything that plugs into the engine computer, the wiring harness or the OBD connector. The manual notes that plug-in telemetry or read-only devices on the diagnostic connector are allowed without an EO.

On July 19, 2021, BAR added a modified software check to its OBD inspection system. BAR's OBD Test Reference says software covered by a CARB EO shouldn't trigger a modified software result. When software is flagged, the vehicle inspection report shows "Modified Software" as the overall result. Once the vehicle is restored to factory software, or to software covered by a CARB EO, it can be retested at any licensed station, unless BAR directs it to a Referee or STAR station.

BAR's Smog Check prep advice says that if your software is modified, restore it to the manufacturer's original settings or to a version covered by a CARB EO.

What CARB's exemption procedures cover

CARB has an exemption category for engine control module programmers and signal modifications. Its procedures also ask manufacturers of devices that change engine, body or transmission control software to plan how they'll collect vehicle identification numbers from buyers' vehicles.

Practical steps

1. Identify the device. Does it reflash software, alter signals, or only read data?
2. Find the EO label and device part number. Check the under-hood label, the device and the box.
3. Note what's loaded. Record the tune name or version and the date.
4. Read the EO at CARB. Confirm your vehicle is listed, then read the conditions.
5. Keep the factory software in mind. If your device saved your original software, record where it is.
6. Questions? Ask CARB at (800) 242-4450. To dispute an inspection result, BAR points owners to the Smog Check Referee at (800) 622-7733.

The Smog Check inspector and BAR's inspection system decide at inspection, and CARB decides which software receives an EO.

What Showgone can and can't do here

Showgone lets you keep your tuner's receipt, label photo, EO number and notes on what's loaded, with a link to check the EO at CARB. Showgone isn't CARB, BAR, the DMV or a smog station, and a Showgone record isn't an official certificate.

Add this part to your free Showgone garage.

Not legal advice.

Sources

• BAR: Smog Check Manual (April 2025), Appendix C (Computer Management)
• BAR: On-Board Diagnostic Test Reference, Modified software standards
• BAR: Smog Check: When you need one and what's required (How to prepare)
• CARB: Procedures for Exemption of Add-On and Modified Part(s) for On-Road Vehicles/Engines (adopted June 29, 2021), Sections III(a)(3) and III(b)(8)
• CARB: Aftermarket parts lookup

Date checked: 2026-10-20