Why The Smog Test

Smog testing is a requirement every two years. The DMV mails out registration notices that remind you about smog testing every other annual re-registration mailing. The notice will tell you whether or not you must have your test performed at a test-only station or if you can go to any testing center. Test-only stations are just as they sound: they do not offer repair or tuning services in the event that you fail your test. STAR smog check stations, equipped with the latest testing devices, are ready to check your vehicle.

You get two attempts at passing. If you fail the first time, you retune/repair the engine and you are allowed to retest for free at the same test station. Be sure to ask your test-only station if they will do this for you and report them if they don’t. Beyond two fails you must take the vehicle to a special government approved repair shop (there are hundreds).  To solve this problem, we recommended making sure you go to a STAR smog check station.

 If you are near your registration deadline and have not passed your test or even taken it, you can still re-register your bus but they only give you a month of grace to complete your test. If you pass during the grace period you must re-register in person. If your leave your test to the last minute you won’t receive your renewal stickers in time so it’s best to go to the DMV early in the morning (when it opens is best). If you are an AAA member you can go to any of their field offices that offer DMV services, pay the fees and receive your stickers in person.

There are 3 components to the test:

1. Emissions test
2. Visual inspection
3. Functional tests

None of the tests can begin until they locate and scan your BAR sticker. If you lack this sticker it means you have an out of state vehicle that has never been tested or it has been removed. You must make an appointment with the smog referee in this situation.

The air-gasoline combustion chemical equation is quite complicated but general air quality is effected the emissions of three by-products due to incomplete combustion: hydrocarbons (HC), carbon monoxide (CO) and various nitrous oxides (NOx). The gas sniffer used by the smog tester has the ability to detect all three emissions simultaneously.

The emissions test is where they insert a probe into the tailpipe to sniff for combustion byproducts and attach a coupler to any spark plug wire to measure engine rpm. With those two items attached they begin the test on the dyno.

The computer automates the testing and the smog tech simply uses a remote control to communicate with the computer from the driver’s seat. The first stage revs the engine to 15 mph and they hold it there while the sniffer does its job. The tech has to shift the bus into 2nd gear to accomplish this. The computer then cues the tech to bring the engine to rest for the second run. The second time, the steps are repeated and the computer requests the speed be raised to 25 mph for a few moments (3rd gear).

Each smog testing shop is supposed to calibrate their tester every 72 hours. Be sure to ask them about it. I don’t know if the computer compensates for temperature variations but that would be something you could ask as well. They are also supposed to use a large cooling fan above 72 F ambient temperature but since our VWs don’t have a radiator this isn’t necessary.

After the dyno testing, they perform a visual inspection. The visual inspection determines if any emission devices that were factory installed are missing. Although the list is long, only a subset applies to each model but if you are missing any item you will fail the test, unless the smog technician fails to notice that you require it when it’s missing (don’t gamble that this will happen for you). How can this happen? Because these vehicles were built before a lot of smog technicians were even born, many will find the engine compartment unfamiliar to them.

The functional inspection includes a check of the timing and idle speed. The idle speed has to be within the manufacturer’s guidelines and the timing has to be within 3 degrees of the specification otherwise you will fail. This is the simplest of tune-ups to perform but some people drive to the testing center, cross their fingers and fail. They will also test the gas cap to see if it seals and check for the presence of any fuel pipe restrictions if applicable. It is always recommended to use STAR smog check .

Be sure they know how to test the timing by clamping onto spark plug wire #1 or #3. If they do not, the timing mark will not appear and they may simply decide to fail you when the timing is indeed within spec.

A few years ago, the visual inspection was done first. At that time the testing was aborted any time you failed one of the stages in order. The benefit to the owner was that if you failed for something simple you wouldn’t risk being tagged as a gross polluter (if you produced excessive emissions). The problem for the government was that they failed to collect any tailpipe emissions data in the process and so they have reversed the testing order.