Want to pass your California smog check the first time? Follow these practical pre-test tips for check engine lights, batteries, readiness monitors, modified software, and more before visiting Smog Tech Pros in Rancho Cordova.

How to Pass a California Smog Check the First Time

Nobody wants to fail a Smog Check, repair the problem, and come back for another inspection.

While there is no trick that can make a vehicle with an emissions problem pass, there are several simple things you can do before your Smog Check to avoid unnecessary failures.

California's Bureau of Automotive Repair recommends checking important items such as the check engine light, battery history, readiness monitors, and vehicle software before the inspection. 

Here are some practical tips to give your vehicle the best chance of passing the first time.

1. Make Sure the Check Engine Light Is Off

This is the most important place to start.

If your check engine light is on because of an emissions-related problem, your vehicle will not pass the California Smog Check.

BAR specifically advises motorists to have the problem repaired before the inspection. 

Do not simply erase the trouble code right before going to the smog station.

That can create another problem.

2. Don't Clear Your Codes Right Before the Test

Using a scan tool to clear diagnostic trouble codes—or disconnecting the battery—may turn the check engine light off temporarily.

But it also commonly resets the vehicle's readiness monitors.

Readiness monitors are self-tests performed by the vehicle's onboard computer to verify that emissions systems are functioning correctly. Those monitors may need to complete before the vehicle can pass the OBD portion of the Smog Check. 

So clearing codes shortly before the inspection can turn a repairable issue into an automatic trip back later.

3. Recently Replaced or Disconnected the Battery? Wait Before Testing

This catches a lot of drivers.

If your battery was recently:

• Replaced

• Disconnected

• Completely discharged

• Jump-started after going dead in a way that caused the computer memory to reset

your vehicle's readiness monitors may have reset.

California BAR recommends driving the vehicle for a week or two after disconnecting or replacing the battery before getting the Smog Check. 

There is no guaranteed number of miles because different vehicles require different driving conditions to complete their monitors. BAR notes that monitor completion can depend on speed, temperature, engine load, pressure, and other conditions. 

Quick tip

If you know your registration is coming due, avoid disconnecting the battery right before your Smog Check unless it's actually necessary.

4. Make Sure Your Readiness Monitors Are Ready

A vehicle can have no check engine light and still have incomplete readiness monitors.

This commonly happens after:

• Clearing trouble codes

• Battery replacement

• Battery disconnect

• Recent emissions repairs

BAR's current OBD reference explains that readiness monitors must run again after repairs or battery-related resets. 

If you have access to an OBD scan tool, you can check the monitor status before going for the official inspection.

If you're unsure, having the status checked before testing may save you a return trip.

5. Don't Try to “Trick” the Computer

Older advice on the internet sometimes tells people to disconnect their battery to erase trouble codes right before smog.

That is usually a bad idea on modern vehicles.

For many 2010-and-newer vehicles, California also checks applicable Permanent Diagnostic Trouble Codes.

Unlike ordinary codes, permanent codes cannot simply be erased with a scan tool or by disconnecting the battery. The vehicle's computer must verify that the underlying problem has actually been corrected. 

The best solution is to fix the actual problem.

6. If Your Car Has Been Tuned, Make Sure the Software Is California-Compliant

Performance tuning can create another unexpected Smog Check failure.

BAR specifically advises owners with modified software to restore the vehicle to either:

• The manufacturer's original software configuration, or

• A version approved by the California Air Resources Board.

Modified or non-approved software can cause the vehicle to fail the Smog Check. 

This can be important for performance cars, diesel trucks, and vehicles with aftermarket tuners.

7. Check for Obvious Emissions Equipment Problems

A California Smog Check may include a visual inspection of applicable emissions-control equipment.

Before your test, look for obvious problems such as:

• Missing catalytic converters

• Disconnected emissions hoses

• Damaged or removed emissions components

• Improper aftermarket equipment

• Loose or damaged components

BAR has identified missing or incorrect catalytic converters, tampered emissions equipment, and non-approved aftermarket parts among common causes of inspection problems. 

If you recently had a catalytic converter or other emissions part replaced, make sure the replacement is legal for your particular California vehicle application.

8. Make Sure the Vehicle Is Safe to Test

A smog technician can decline to test a vehicle that presents an obvious safety hazard.

For applicable older vehicles receiving tailpipe testing, BAR requires inspectors to verify that there are no obvious safety hazards before the test begins. 

Before coming in, make sure your vehicle doesn't have an obvious problem such as a severe fluid leak, unsafe tire condition, or another condition that could make operating it during the inspection unsafe.

9. Drive the Vehicle Normally Before the Test

For vehicles that undergo a tailpipe emissions inspection, the engine needs to reach normal operating temperature before the emissions test.

BAR's Smog Check Manual requires applicable vehicles to be warmed to normal operating temperature before tailpipe testing. 

So bringing an older vehicle in after normal driving can be preferable to having it arrive completely cold after sitting for a long period.

You do not need to race the engine, drive aggressively, or attempt to overheat the catalytic converter.

Normal operation is enough.

10. Don't Make Last-Minute Repairs Unless Necessary

One of the most common mistakes is doing emissions work right before the Smog Check and immediately heading to the station.

For example, if a repair requires codes to be cleared, the readiness monitors may not have had enough time to rerun.

After emissions-related repairs, make sure:

1. The underlying problem is actually fixed.

2. The check engine light stays off.

3. The appropriate monitors have completed.

4. The vehicle has had enough normal driving time.

Then get the official test.

11. Check Your Smog History Before Coming In

You can check your vehicle's previous California Smog Check results using BAR's official Vehicle Inspection Historytool.

Searching your VIN or license plate can help you see previous inspections and results.

On smogtechpros.net, use our Check Your Smog History link to go directly to the official BAR database.

This can be especially useful when you aren't sure when the vehicle was last inspected.

12. Don't Ignore Your DMV Notice if It Says STAR

Look carefully at your registration renewal notice.

If it says:

“Smog Certification Required at a STAR Station”

you must use a STAR-certified Smog Check station.

Going to a non-STAR station won't satisfy that DMV requirement.

Smog Tech Pros is STAR Certified, so we can inspect vehicles specifically directed to a STAR station as well as regular Smog Check vehicles.

Things That Do NOT Guarantee You Will Pass

There are plenty of internet “smog tricks” that sound convincing but don't repair an emissions problem.

Don't assume these will make a failing vehicle pass:

• Putting premium fuel in a vehicle that normally uses regular

• Disconnecting the battery

• Clearing the check engine light

• Adding random fuel additives

• Driving extremely hard immediately before the test

• Replacing parts without diagnosing the problem

A Smog Check evaluates the actual emissions-control system and, on applicable vehicles, information reported by the vehicle's onboard computer.

The safest approach is a properly maintained vehicle with no known emissions problems.

Quick Smog Check Checklist

Before heading to the station, ask yourself:

✓ Is my check engine light off?

✓ Has my battery been connected normally for at least several days?

✓ Have I avoided clearing codes immediately before the test?

✓ Are my readiness monitors complete?

✓ Is my vehicle's software stock or CARB-approved?

✓ Are my catalytic converter and emissions components present and properly installed?

✓ Does my DMV notice require a STAR station?

If everything looks good, you're giving your vehicle a much better opportunity to pass the first time.

Frequently Asked Questions

Should I drive my car before getting a smog check?

Normal driving is fine. Applicable older vehicles receiving tailpipe emissions testing need to be at normal operating temperature before the emissions test. 

How long should I drive after replacing my battery?

BAR's general consumer guidance recommends driving the vehicle for a week or two after disconnecting or replacing the battery so readiness monitors have an opportunity to reset. 

Can I clear my check engine light right before smog?

That is not recommended. Clearing codes can reset readiness monitors, and permanent diagnostic trouble codes on applicable vehicles cannot simply be erased. 

Will my car pass if there is no check engine light?

Not necessarily. The vehicle still has to satisfy the other applicable visual, functional, OBD, or emissions requirements.

Should I use a fuel additive before a Smog Check?

There is no fuel additive that guarantees a passing California Smog Check. If the vehicle has an emissions problem, diagnosing and repairing the problem is the appropriate solution.

Do I need an appointment at Smog Tech Pros?

No. Walk-ins are welcome.

What happens if my vehicle doesn't pass?

Smog Tech Pros includes a free retest, subject to applicable restrictions, after you correct the problem.

Ready for Your Smog Check in Rancho Cordova?

If you've gone through the checklist and your vehicle is ready, bring it to:

Smog Tech Pros
10751 Folsom Blvd
Rancho Cordova, CA 95670
916-638-4700

STAR Certified • No Appointment Necessary • Free Retest Included

Found another smog coupon in Rancho Cordova?

We will match or beat any coupon in Rancho Cordova.

Restrictions apply.

For official preparation guidance, see the California Bureau of Automotive Repair's Smog Check information.