Top 5 Reasons Smog Checks Fail (And How to Avoid Them)

Nobody wants to fail a smog check. The good news: most failures are easy to see coming. Here are the big five and how to dodge them.

1. Your check engine light is on

If that little light is on, your car will fail. Get it looked at by a mechanic first. Here’s what to do.

2. Your car’s computer says “not ready”

If your battery died, was replaced, or a mechanic cleared codes recently, your car’s computer resets. It needs a few days of normal driving to finish its self-checks. Test too soon and you’ll get a “not ready” result.

Tip: Drive normally for a few days (often 100 to 200 miles, with some freeway time) before you come in.

3. Aftermarket parts that aren’t approved

Intakes, headers, tuners, and exhaust parts need a CARB approval number, called an EO number. Without one, it’s an automatic fail. Check with whoever sold you the part.

4. Skipped maintenance

Old oil, dirty air filters, and worn spark plugs can push your emissions up. Staying on your regular service schedule really does help.

5. Ignoring a problem

Rough idle, sputtering, or a strange smell won’t fix itself. Get it checked before your smog.

If you do fail

Don’t panic. We’ll walk you through what the test found. You can take it to any repair shop and come back for a retest. If repairs are pricey, California’s Consumer Assistance Program may help pay for them.