Understand the California Smog Inspection

***Please note that the laws are constantly changing and this information may not be updated with the latest rules and regulations.


There’s a lot of misinformation floating around about the smog test process.  The following is a clarification on the majority of questions we encounter.


1) There are technically three smog “zones” in California.  A few small areas have no smog inspection because of the higher air quality in those areas.  In the bigger city areas, where air quality is at its worst, there is the Enhanced Smog Inspection, which tests five gases (oxygen, carbon dioxide, hydrocarbons, carbon monoxide, and nitrogen oxide) and runs the test on a chassis dynamometer.  In Basic Smog Inspection areas, such as ours, the smog test includes only probing for four gases (the above, less nitrogen oxide) and runs stationary.  If your vehicle is registered in an Enhanced area, a Basic smog station CANNOT run your smog test.  The smog machine will not allow it.  You must either change your registration address or find a station equipped and licensed to run the Enhanced Smog Inspection.  If you change your registration address, that change normally takes a few days to a few weeks to take effect.  In order to expedite that, it is highly recommended that you go to your local DMV office in person, file the address change, and receive a printout from the clerk showing the vehicle information, the new registration address, and a barcode across the middle or top of the page.  Bring this sheet with you back to your smog inspection station, and the smog technician can log into a website to force through the address change immediately and run the smog check.  Otherwise, you’ll have to wait the weeks for the change to go through, and cannot smog your vehicle until that change takes effect.


2) When selling a vehicle, it is the SELLER’s responsibility to have a vehicle smog checked on or before transfer of ownership.  Even if a seller and buyer make a deal that the buyer is going to smog it, any problems smogging the vehicle can legally go back on the seller.


3) A smog certificate is only good for 90 days.  If you smog your vehicle and fail to complete your registration with the DMV, and 91 or more days elapse, you WILL have to smog it again.


4) There are three reasons to smog a vehicle: Biennial (every other year for your DMV renewal of registration, which starts when a vehicle turns 6 or 7 years old); Change of Ownership (unless it’s a blood-relative transfer with the same last name, a vehicle must be smogged to change ownership; note: this does NOT alter the preset Biennial smog schedule for the vehicle; so if you buy a vehicle and six months later it comes due for it’s Biennial test, it will have to be smogged again even though it was just smogged six months prior for the transfer); Initial Inspection (bringing a vehicle into California requires an additional smog inspection; again, this will not alter its Biennial smog schedule).


5) There are three components to the smog inspection (note: we are focusing on the Basic program here).  First, there is the visual inspection: determine that all required smog devices are in place, and any aftermarket modifications are legal (note: any aftermarket modifications, such as an air cleaner, catalyst, headers, etc. MUST be tagged with an Executive Order label indicating that the part is a legal replacement unit for California; if not, it WILL fail the smog test on that technicality).  Second, there is the functional test, which checks to make sure all required smog devices are functioning as designed.  Third, and this is the part most people focus on, is the tailpipe probe to check the emissions levels (primarily hydrocarbons and carbon monoxide — and note that as of 2015, this portion of the test no longer applies to vehicle models 2000 and newer).


6) Failing smog does not necessarily mean it’s a Gross Polluter.  When it comes to failing the tailpipe portion of the smog test, there are two failure “levels”: there is a basic failure, which means the hydrocarbon or carbon monoxide count is above the maximum allowable level, and there is a second, higher Gross Polluter level, in which case the tailpipe emissions are considered Excessive.  If a vehicle fails smog, it has to be diagnosed, repaired, and retested.  If it fails as a Gross Polluter, however, it has to be diagnosed, repaired, retested, and then retested again at a Gold Shield or State Referee station to have the GP status cleared.  Generally, as long as a vehicle is running well, the check engine light is not on, and the battery has not been recently disconnected or gone dead, a vehicle will likely pass smog.  If it’s running very poorly, a pretest would be highly recommended.


7) A pretest, as the State wants it done, is essentially a smog test without a certificate.  It requires running the full smog test procedure, not just a quick tailpipe probe.  Some people expect that a shop will run a quick $10 precheck of the tailpipe emissions, but this is technically not permitted.  Again, this is a State regulation, since they want pretests logged in the system for statistical purposes, and a quick tailpipe probe won’t log any information with the State.  If you want a pretest on a car, expect a proper procedure and extra charges for the extra machine and labor time involved. Note that, as of legal changes in 2015, a pretest is no longer available on vehicle models 2000 and newer.


8) Whether a vehicle passes or fails the smog inspection, the test results ARE reported to the State.  There is no way around this.  We’ve had people request that a smog test be run but not have the results reported — this is not only impossible by the programming of the smog machine, it’s also not permitted.  Also, whether a vehicle passes or fails, you should always be given a paper copy of the smog inspection test results, showing the three components of the smog test and their outcome.  Keep this paper copy in your records.  The test results are transmitted electronically to the State (smog check stations are required to have a dedicated phone line just for the smog machine for this purpose) but every once in a while, as with any technology, there can be transmission errors.  Keeping the paper copy in your records (or particularly in your car, at least until you receive your registration tags) is a good backup in case the test results don’t transmit or get lost in DMV’s system.  Again, this is rare, but it does happen.


9) The State is constantly changing the smog program.  It used to be that any vehicle 30 years old or older did not have to be smogged, so one year model was dropped off the rolls every year.  That law has since been changed, so currently any gas model 1976 or newer has to be smogged.  A few years ago, the Evaporative Leak portion of the smog test was added to the program for 1995 and older vehicle models, so there is more time and equipment involved in running a smog check on those models (there are a few exceptions, such as a vehicle that has dual gas tanks).  We are also now smogging diesel models (currently anything 1998 or newer with less than 14,000 GVW).  In 2015, new changes were made dictating different test procedures for vehicle models 2000 and newer, as well as changes to requirements for various gas and diesel models, as well as adding in the hybrid models.  Shops must stay up-to-date on the constantly changing regulations and smog test procedures.


10) If your Check Engine or Service Engine Soon light is on, your vehicle WILL fail the smog test.  Also, on 1996 and newer models, disconnecting the battery or clearing codes immediately before a smog inspection will be a cause for failure.  See our previous note about check engine light diagnostics for more information on this (diagnostics, monitors, drive cycles, etc.).


11) Not all shops have a “Pass or don’t pay” program.  That is an optional offer that some shops have, however most do not work that way.  We’ve heard people claim that it is a State requirement that a retest be free — this is NOT true.  If a vehicle fails smog and has to be fixed and retested, the retest is extra technician labor and use of the smog machine, so there are costs involved for the shop to run a smog test.  It’s very expensive to be in business, so try to be understanding if a shop does not offer retests for free.  If you don’t want to pay for a second test, do your homework ahead of time to find a shop that is willing to offer work for free.


12) Smog check labor charges vary by shop.  However, the smog certificate fee (currently $8.25) is set by the State and cannot be charged otherwise.  If you do not pass the smog test, there should be no certificate fee — you’ll only pay for the technician’s labor time for a failed test.  If a shop charges you anything other than $8.25 for a certificate fee, contact the Bureau of Automotive Repair.  Note: the smog certificate fee is not taxable, so there should also be no sales tax charge on a straightforward smog inspection.  Currently, anyway.  There are rumors going around about the State attempting to create a sales tax on labor in the automotive industry.  The industry is trying to keep this proposed law at-bay since it will only create more expense for shops and the general public.


13) If you’re going to call around to various smog check shops to compare prices, make sure you’re comparing apples to apples.  Some shops will advertise “Just $39.75 for a smog inspection!” but in the fine print it says “Plus Certificate”.  Other shops will clearly advertise “$45 for a smog inspection, including certificate”.  So if you hear $39.75 at one shop and $45 at another, but neither specifies whether the certificate is included or not, make sure you ask so you don’t walk into the shop that sounds cheaper and then get hit with a surprise of a larger bill once the certificate fee is added in.


14) If a vehicle fails smog, it will likely require some form of diagnostic to determine what repairs are needed.  Please note that, by law, smog-related repairs must be conducted by a licensed smog technician.



Also, a few tips to make your smog inspection appointment run smoothly:

1) Call ahead of time.  Depending on a shop’s schedule, sometimes you can walk in and get a smog, but it’s easier to have an appointment set.  Plan on the test taking about 20-30 minutes.

2) Bring your DMV renewal notice.  This can help prevent data input errors and can make the paperwork process much faster, both at the service counter and at the smog machine itself.

3) Plan on taking a few minutes to talk to the Service Writer and sign an estimate.  Just as with any automotive services you get, you must give your contact information and sign an estimate before anything can be done on your car.  Don’t expect to just drop the keys and leave.

4) Make sure the gas tank is at least 1/4 full.  Coming in for a smog test with the tank on Empty is risky — don’t want to run out of gas in the middle of the test! — not to mention damaging to the vehicle (having at least 1/4 tank at all times keeps the fuel pump cooled as well as keeping debris that settles in the bottom of the tank from being picked up by the fuel pump and delivered throughout the fuel system).  Also, one of the computer monitors on any 1996 or newer vehicle will only run if the gas tank is between 1/4 and 3/4 full, so this is just another reason to never let your tank go to Empty.

5) If your battery has died or been disconnected in the last week or so, or if codes have been cleared recently, tell the Service Consultant since this is a potential failure area — a technicality, but a failure nonetheless.  If a vehicle’s memory has been cleared, it will need to complete a drive cycle before it can pass smog.

6) If you have any aftermarket equipment on your vehicle, make sure the parts have affixed tags clearly showing the Executive Order number, and preferably keep in the glove box any paperwork that came with the parts.  If there is any doubt that an aftermarket part is legal, the smog technician will need to research its legality before proceeding with the smog test.  If it cannot be proved to be legal, the vehicle will fail the smog test on that technicality.

7) Sometimes, at the service counter, we’ll ask if the check engine light has been on recently, and people will lie and say it has not, when in fact it was and they cleared codes to turn out the light just before coming in.  The vehicle does not lie.  With the advanced computer systems on cars today, it’s very easy to see if computer memory has been reset, not to mention the vehicle will fail the smog test if the memory is empty.  You’re not saving yourself anything by trying to hide something that the vehicle will reveal regardless.


A lot of information, but as the smog program expands, it becomes more involved and more technical.  Hopefully this note covers most of the questions normally asked in regards to the smog inspection.  Have a question that’s not covered here?  Just ask!