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Smog Test FAQ

Smog Test Owner looking over the results

What You Should Know About Smog Tests

For More Questions About Smog Tests, Contact Us Today!

Q: What is Test-Only?

A: Test-Only is a special classification of independently owned smog station that performs an unbiased emissions inspection. Test-Only facilities do not perform any repairs, adjustments or diagnosis and are not permitted to give referrals to repair facilities or to offer specific repair advice.

Q: How is Test-Only different from “regular” smog places?

A: “Regular” test-and-repair stations cannot certify “Gross Polluter” vehicles or other vehicles with STAR test requirements. Many people feel that a conflict of interest exists when a business is allowed to both repair and certify a vehicle. This could be comparable to allowing a contractor to be the building inspector on his own projects. Test-Only stations do not have this conflict of interest since no repairs can be performed.

Q: Why was my car selected for STAR inspection?

A: About 1 in 3 of all vehicles due for smog inspection in the states smoggiest areas are directed to STAR Test facilities. This requirement was created to comply with the Federal Clean Air Act. Some of the vehicles that make up this percentage may have had emissions failures in the past while others may have been selected at random or from a list of vehicles that fit a statistical model called a High Emitter Profile (H.E.P.). The H.E.P. was created using data collected over the last 25 years from smog checks, roadside inspections and studies commissioned by the state and federal governments.

Q: My car doesn’t smoke, why does it need to be checked?

A: The gasses that combine with sunlight to form smog are not visible when exiting the vehicle tailpipe. Smoke from the tailpipe would be an indication of a possible problem but may not be related to smog forming emissions. To report a smoking vehicle you can call 916-END-SMOG (363-7664) or #SMOG (7664) from your wireless phone.

Q: If my car fails, am I automatically a gross polluter?

A: Only vehicles that fail and have emissions that exceed the gross polluter standard are considered gross polluters. More importantly, vehicles that fail at levels above the gross polluter standards are not held to a tighter standard on the retest. All that is required of these vehicles will be to repair the emissions failure and retest the vehicle at a STAR test facility like ours.

Q: Why are prices so different from one smog station to another?

A: Most test-and-repair stations make the bulk of their profits from repairs. Many test-and-repair facilities use smog check prices as advertising or “loss-leaders” to draw in business with the hopes of selling more profitable repairs. The prices charged by Test-Only stations more accurately reflect the cost of providing the inspection service without up-sells for repair services.

Q: Can a Test-Only Center certify any car, or just gross polluters?

A: STAR Test-Only Centers can inspect and certify ALL cars, trucks, vans and motorhomes regardless of the required certification status.

Q: Why did my car fail the visual or functional inspection even though the emissions passed?

A: The emissions test is performed in up to 3 parts. Tailpipe emissions are tested under specific speed and load conditions. While these conditions simulate various normal driving conditions, not all conditions can be simulated. In order to make sure that your vehicle runs clean under all conditions, ignition timing must be correct and all the manufacturer’s emissions equipment need to be in place and functioning. This is the reason we perform the comprehensive visual inspection and functional testing.

Q: Why does the gas cap on my car need to be tested?

A: The gas cap on most vehicles is designed to hold fuel vapors inside the fuel tank and fuel evaporation system. When a gas cap fails to hold sufficient pressure, the fuel evaporation system cannot operate as it was designed. This results in evaporative emissions which contribute significantly to smog formation.

Q: My check engine lamp is on, why does that make it fail the inspection?

A: The purpose of the malfunction indicator lamp (this may appear on the dash as a check engine or service engine soon lamp) is to inform the driver that the vehicle computer has detected a problem that may be emissions related. Correct operation of the self-diagnostic portion of the computer system is just as important as the rest of the emissions system. The easiest quick check of the self-diagnostic system is to make sure that the check engine lamp functions as the manufacturer intended.

Q: I have been told that my car will fail because the “Monitors are not set”. What does that mean?

A: “Monitors” are the industry term for the self-testing protocols that 1996 and newer vehicles perform during normal driving conditions. Any time that one of these vehicles experiences a problem that turns on the check engine lamp or any interruption of power to the vehicle computer these self-tests will need to run to completion. Dead or disconnected batteries are the #1 cause of this problem. Running the “monitors” to completion usually requires nothing more than normal driving under the right conditions.

For most cars, this will mean driving the vehicle under normal conditions for 1 to 2 days. It is recommended that this includes at least 1 vehicle start after sitting overnight and that the fuel level be between 1/4 and 3/4. If during this time, the battery is discharged or disconnected this process will need to be started over. Additionally, if the check engine or service engine soon lamp comes on while driving or idling, repairs for this fault will be required prior to setting monitors.

Q: I lost my paperwork from my last smog. Can you provide me with a copy?

A: A full history of tests performed on your vehicle is available by visiting the California Bureau of Automotive Repair web site at The link is listed as “Find Vehicle Smog Test History” and is currently one of the links on the consumer tab at the top of the home page.

Q: Why am I required to have my diesel tested?

A: Testing of 1998 and newer diesel powered vehicles began in January 2010. The test we are performing differs slightly from earlier gas powered vehicle testing in that we will not be sampling the exhaust contents or performing “loaded mode testing”. Visual and functional testes are still being performed. This means that many popular diesel engine modifications may cause the vehicle to fail the inspection.

Q: I bought my diesel powered pick up with the modifications already performed. Will I need to return the vehicle to “stock” in order to pass the emissions test?

A: All emissions related modifications must be done using state approved parts that carry a California Air Resources Board (CARB) Executive Order number. Modifications that were done with non E.O. parts will cause a failure of the visual inspection and will need to be corrected to pass. Any non-legal modifications performed by the prior owner or seller were not legal then or now and you may have some legal recourse. More information can be obtained by contacting the California Bureau of Automotive Repair at 916-255-4200.

Q: Why did my car fail for an incorrect Catalytic Converter?

A: Incorrect catalytic converter installation has been a very common problem in past years and often leads to multiple catalyst failures over time. Beginning in January 2009, Catalyst manufacturers were required to label all of their products with the associated Executive Order (E.O.) number. This number identifies each part as it was approved for use on a specific vehicle model. As part of our visual inspection procedure, we are required to verify that the correct replacement part was installed.

Q: Will my car pass if I have installed performance upgrades?

A: Many popular upgrades can be performed legally by purchasing performance parts that have been approved by the California Air Resources Board (CARB). Approved parts are issued an Executive Order (E.O.) number and this should be provided to you at the time of sale in the form of a stamping on the part or a sticker that is intended to be placed under the hood in a visible location. Almost all emission system modifications that do not include this E.O. number will cause the vehicle to fail the visual inspection. Information about approved parts is available at

Q: What is the Functional Evap Test and why does my car require it?

A: The fuel evaporation system on your car is intended to prevent fuel vapors from escaping into the atmosphere and evaporative emissions represent a significant portion of smog forming gasses. On 1996 and newer vehicles, each vehicle is designed to perform self-tests to assure that these systems are functioning as designed. For older vehicles, the state has designed a “functional evap test” that we perform during the course of your smog inspection. This simple test uses nitrogen gas to check for leaks in the fuel evaporation system on your car.

Visit the location nearest you today for more information. For Orangevale, call 916-989-0101. For the North Highlands, CA location, call 916-332-9900

Tailpipes Smog Test Centers

7460 Watt Ave.
North Highlands, CA 95660
Phone: (916) 332-9900

Hours of Operation:

Mon – Sat          8:00 am – 5:30 pm
Sunday                                   Closed

Motorhomes Taken Only Until 10am
No Pass No Pay
Does not Apply to Motorhomes

9292 Greenback Lane
Orangevale, CA 95662
Phone: (916) 989-0101

Hours of Operation:

Mon – Sat                  8:00 am – 5:30 pm
Sunday                     Closed


4 Star Rating

Shalome P. On 08.02.2017
JR was very welcoming and explained the process as it was my first time getting a smog. I am glad he was there for me. Shalome

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