Monitors are tests that the computer performs while you drive. Their purpose is to 'test' the engine controls and emissions systems to be sure they are not polluting. The Feds don't care how you car runs, only that it is not producing excessive emissions. And of course this is only applicable if you are in an Emissions Compliant County. The Car manufacturers must meet Federal and/or California emission standards in order to build the cars. The current system in use since 1996 is known as OBD2 which stands for On Board Diagnostics 2 which is the second system instituted to monitor emissions to ensure compliance to the standards.
OBD1 would only show you a failure. Sometimes the light would go off and often leave no trace of a problem. OBD2 solves that and more by recording multiple failures and if the minimum threshold is reached, then the light will set. OBD monitors all systems, not only ones that make your vehicle run badly. So things like Alcohol Sensors or Catalytic Converters that do not affect drivability, but are required to ensure low emissions can cause you light to come on. Some Chryslers would set the light if the Lock Up Converter failed in the transmission! Even though it did not affect emissions at all! Only your gas mileage!
Monitors must run [little programs that test your vehicle] and have the required number of passes to be considered compliant. There is no simple way to do this for the DIYr. The tests are performed when you drive, and it requires certain requirements to be met. Catalysts are tested at about 50mph, some O2 heaters are tested after the car is turned off! Evaporative systems are tested only when you start for some cars, and others require driving at speed also! Every car is different. The driving that is required to complete monitors can be complex. The name for that driving is Drive Cycles.
So, now you are wondering, "How can I know when it is ready for inspection?"
Usually I tell folks to drive for a day, come by the shop or an inspections station and have them check the monitors to see if it is ready to pass. Many shops will do this as a courtesy, some parts stores and some inspection stations will also. Most OBD2 vehicles will pass with 1 monitor incomplete, but this depends on your State and your area where you drive.
It might be good to note now that if you have a fault, and do not fix it, the chance is the CEL will re-illuminate after driving. Just turning the light off will not make it inspect. You have to FIX the problem that causes the CEL to come on. Depending on the failed part, this could be quite costly! Catalytic Converters are very expensive and can cost of $2000! A alcohol sensor can cost $1000.
If you want your car to run clean, and the systems designed to monitor it to function properly, then you must fix the car. It is true that emissions may not be affected by the failure, but the LAW says if it could LEAD to increased emissions you must fix it. Otherwise you can write your representative at the State Legislature and argue that the costs of maintaining the vehicles is absorbent and a burden to the citizens, or the manufactures that charge high prices for their parts!
I believe that we can build cars that run clean and they do, but the price for an exhaust that emits only CO2 and water is high. But we are there now. Perhaps we can push for generic parts. Like Catalytic Converters that are standardized like your light bulbs. I think there are some good ideas that would keep costs down for the consumers, but it is more then federal standards that must be confronted, one must also consider the ideologies of the manufacturers!
So how far to drive to clear monitors? Might be 10 miles, it might be 30 or more; the only way to know is drive. I recommend a day or two of normal driving is usually sufficient. If you want the process to go faster, you need to watch the monitors. I recommend the INNOVA 30203 code reader that can be purchased for $80 or less. This is a great tool and works on any OBD2 compliant vehicle! It will let you see the monitor status and also has colored LEDs; Red is fail, Yellow might pass and Green guarantees your emissions are in compliance!
The 30203 CarScan Code is the ideal entry-level tech tool where nothing more than basic diagnostic and repair verification information is needed. Its shows over 20 pcs of info on its all in one screen, has easy to use features to quickly reveal the cause of "Check Engine" light warnings on any 1996 and newer vehicles, including all those with Controller Area Network (CAN) coverage. The tool has 15 inspection maintenance monitor coverage, shows permanent and pending codes as well as the code which tripped the freeze frame, turns off the check engine light as well as having a simple and easy to understand 3 color LED emissions status check.
Till then, drive, test, pass/fail and inspect!
