How to Pass Your Emissions Test

As a public service, and because we now live in the age of misinformation, where it seems that more than half of what you hear, see or read is completely false, I will now share with you some tidbits about emissions.  For those who live in a state without emissions testing, whose car is super squeaky clean and doesn't have an issue with the "Check Engine" light, or simply don't care, feel free to move on (as if I could stop you anyway).  For the rest of you:

• As of 2003, 33 states, plus the District of Columbia, required emissions testing.  I believe the number is more now, but the actual number is fairly irrelevant to this post, and I'm sure you know if you live in an emissions-testing state.  (State Emissions List)  And if you really, really aren't sure, check here...State by State Emissions Laws
• In order to pass an emissions test, your car has to pass several tests for gas emissions of various types, under varying degrees of engine temperature and speed.  In addition, a vehicle must pass a fairly rudimentary safety inspection.  The one item that isn't rudimentary, however, is that your "check engine" light must be off.  If it is on, the vehicle fails automatically.  
• You may be interested to know that California actually has its own, more stringent regulations those those of the EPA, managed by the California Air Resources Board.  Also, 16 states have adopted those more stringent regulations rather than following EPA standards (technically, if you follow CARB, you are already following EPA standards, as they are less strict).  Emission Standards
• You've probably received advice like this in the past:  What Not to Do.  I encourage you to ignore it.  Also ignore the smogcheck facility guy who tells you to just "run it for 100, 200, 300 miles," or the mechanic who gives you similar worthless "advice."  None of these "fixes" will enable you to pass the emissions test, though there is a slight chance that such measures will turn off your check engine light.
• For every car make (i.e., brand), there is a specific emissions sequence that you can follow to turn off your check engine light, and ensure that your car will pass emissions.  If you're interested in knowing more about it:  Emission Test Cycle.
• The standards aren't going away, but rather they are tending toward worldwide standardization similar to CARB's standards (Emission Standards).

I'm focused specifically on the check engine light, so if you have a problem like your catalytic converter exploding, you'll have to look elsewhere.

So, what's the big secret?  There is none, it's just that it's easier to tell someone to drive their car for a couple hundred miles, in order to turn off the check engine light, than to tell them how to actually drive the car, to pass emissions.  That actually works, if you drive like someone with one foot in the grave.  For the rest of us, you will likely turn off your check engine light, and still fail the emissions test.  Why?  Because your car's computer stores all the information that caused the check engine light to go on, even after it goes off.  The ONLY WAY to erase that information is for you to successfully drive your car under the EPA's testing procedures, several times, without a fault.  And, generally speaking, driving your car around for a few hundred miles won't do it.  

Fortunately, there is an answer to this problem.  Nearly every auto manufacturer sets up the emissions controls in the car to match the EPA's standards.  Why?  Because they don't want you going to get your emissions tested, and failing, because your check engine light isn't accurately portraying how your car is performing.  So, check engine light on, you will fail.  Check engine light off, you will (eventually) pass.  Your mechanic can check the chip in your car and tell you how many faults you still have in the system.  You get a fault or two that are allowed, but beyond that, you fail.  

The good news is that manufacturers publish the actual fault procedure cycles that they use.  I've attached the link here, for two manufacturers (Ford and GM).  If you follow the procedures indicated, your check engine light will go off, and the faults will reset so you can pass emissions testing.  The information I've researched is conflicting, but supposedly, you can perform a partial cycle, and your car's computer will still give you "credit" for that part of the cycle that you complete successfully.  Other sources say you have to complete all steps of a cycle successfully, in order, or you get nothing for it.  I'm not sure - I ran three cycles, separately, in order, and it cleared my faults.  Since I'd already wasted a few hundred miles driving aimlessly to no avail, I had no desire to test the "partial cycle credit" theory.  The following is the "drive cycle reset" procedure for a BMW:

As you might note, the type of driving that will clear the faults is quite specific.  Even though the faults will clear automatically with unintended cycling 40+ times, it seems unlikely that a typical driver would actually achieve that many cycles in their lifetime, in my opinion.  

Here's the short version of the BMW Drive Cycle document (including the chart above):

BMW FTP72 Drive Cycle Procedure for Resetting Computer and Emissions Sensors by Brent Tharp

PLEASE NOTE - if your check engine light won't go out, you most likely have a problem with a part that needs to be replaced.  Hopefully, that part is not a catalytic converter.  

Not every state agrees that emissions testing is necessary, given the much cleaner cars being manufactured today.  That state is Washington....Straight from Tree Hugger Land.

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