Don’t Clear That Check Engine Light—This $100 Tool Can Save You a Failed Smog Test

The “check engine” light is the most annoying orange icon in America. Half the time the car feels fine, and the other half you’re about to fail emissions or get stranded. A good Onboard Diagnostic 2 (OBD2 – the 2 just points to an updated standard) scanner puts you back in control because it tells you what the car thinks is wrong—before you waste money or show up for a test and get bounced. It also helps you decide if it’s safe to keep driving.

This got more serious in 2025. California tightened its OBD readiness rules on October 1, 2025, requiring readiness monitors to be set to pass a Smog Check in many cases. The state explains the change in its BAR readiness monitor regulations update. Even if you don’t live in California, the lesson applies everywhere: clearing codes right before inspection is a great way to fail.

What to Look For So You Don’t Buy Junk

Start with the basics. Any scanner worth owning reads codes and shows live data. The cheap ones stop there. The better ones also show readiness monitors, which are the self-tests the car runs to confirm emissions systems work. California’s OBD Test Reference lays out what readiness monitors are and why they matter.

Next, avoid the “erase code” temptation. A scanner isn’t a delete key. If you clear codes, you reset the monitors, and you may need a full drive cycle to set them again. That’s why a scanner with a clear readiness screen is more valuable than one with a flashy app.

Then pick your format. A handheld scanner is simple and quick. A Bluetooth dongle is compact and often cheaper, but the app matters, and so does your phone. If you want zero fuss, handheld wins. If you like graphs and long-term monitoring, Bluetooth plus a solid app can be great.

Finally, know what an OBD check actually is. CARB explains that a Smog Check includes communication with the onboard computer and checks for faults and monitor status in its OBD II systems fact sheet. That’s the reality your scanner is helping you navigate.

If you want two “can’t-go-wrong” handheld picks, I’d do this:

1) Autel AutoLink AL619
Best if you want more than just check-engine codes. It’s a true handheld step-up because it can dig into ABS and airbag (SRS) faults too—exactly the stuff that sends people to a shop for a “quick scan.”

2) Foxwell NT301
Best bang-for-buck if your goal is engine/check-engine diagnostics + live data + readiness monitors (great for DIY troubleshooting and emissions-readiness checks) without paying for extra system coverage you may never use.

Rule of thumb: if you ever want to diagnose brake/airbag lights, grab the AL619. If you mainly want to kill CEL anxiety and read data, the NT301 is the clean value play.

My Verdict

Buy an OBD2 scanner that clearly shows readiness monitors, not just trouble codes. Use it to understand problems, not to wipe them away. If you live anywhere that tests emissions, this is the cheapest “peace of mind” gadget you can throw in your glovebox.