The article provides the lay person with step by step instructions on how to perform a basic, yet very effective Drive Cycle that will complete the Readiness Monitors for their vehicle's Emissions Control System. The Drive Cycle is a part of the methods used by the Engine Computer or PCM to determine whether an Emissions System repair was properly performed. A Drive Cycle is a special test drive that duplicates a person starting their car and making a short freeway trip, as if they were driving to work. While this special test drive or 'Drive Cycle' is occurring, the Engine Computer runs little tests or Readiness Monitors that check to see if the Emissions System is working properly.

What is the purpose of a Drive Cycle?

When a vehicle has an Emissions System problem, it almost always triggers a Check Engine or Service Engine Soon Light. This signals that an Emission System problem and fault code has been recorded in the Power Train Control Module or PCM. This Emissions System problem, indicated by the fault code, must now be accurately diagnosed and repaired.  After the proper repair has been completed and the fault code cleared, the Power Train Control Module or PCM will run a series of self-tests during a special test drive called a Drive Cycle.  These tests that are run during the Drive Cycle, are to determine whether or not the repair actually corrected the problem and whether the various Emissions Systems are 'Ready' to be trusted. If the Emission Systems are 'Ready' then they are put back in to the service of minimizing the Emissions released in to the atmosphere from the vehicle's operation. This process is how the term 'Emissions Readiness Monitors' was derived.
                This process was designed to prevent a vehicle from slipping through an Emissions Test with a known Emissions problem. Until 1996, a common tactic was to turn off the Check Engine Light just by clearing the code just before an Emissions Test, with out performing the proper repair. The Drive Cycle and Emissions Readiness Monitors have, for the most part, stopped this unethical tactic.

How to do a basic Drive Cycle

       Step One, how to prepare your vehicle

• Have the fuel tank between 30% and 70% full. This is because some of the systems, especially the EVAP System, need to have a specific level of fuel in order for the tests to be trusted. If the fuel tank is near empty or completely full, many of the basic tests will not run at all!
  
• The vehicle must also have a good Alternator and a strong Battery. If you have to occasionally jump start your vehicle, then this erases all of the memory from the Power Train Control Module or PCM. The PCM stores data in order to accurately track the results from various stages of the Drive Cycle. Also, if the Battery is weak or under charged, then some of the most important tests will never, ever run. This is a crucial.
  
• The vehicle must sit over night for at least 8 hours, in an environment that is less than 90 degrees Fahrenheit. This is so that the Engine Temperature can match the Air temperature in order to establish an accurate base line for the testing that occurs during the Drive Cycle. If the outside temperature is over 90 degrees, the fuel remains too volatile and the EVAP System won't even try to run its tests, though some of the other Emissions Systems MAY run their tests.
• The keys must be out of the Ignition and all of the doors must be closed while the vehicle sits over night. Many of the on board Computers 'boot up' when the keys are inserted into the Ignition. Also, many of the on board Computers still run until all the doors are closed AFTER the vehicle is shut off and the keys are removed.

       Step Two, the cold start

• Start the vehicle and let it idle for 2-3 minutes in Park or Neutral. While it is idling, turn on the Headlights and turn on the Heater/Defroster and Rear Defroster for a 3-5 minute warm-up phase. Let the idle speed settle down to near the normal speed. 
• Next, put the vehicle in gear and drive through city streets. See if you can go up to about 35-40 mph and at the normal city speed of 25 mph a few times before slowing down to stop. Don't roll through the stop, be sure the car is really stopped, just like you are in driving school. Accelerate from each stop in a normal fashion not overly conservative but not like a drag race either.

      Step Three, a short freeway trip

•  After the vehicle has been cold started and driven for a few miles on city streets, the next step is to take it on a short freeway trip.
  
• Enter the freeway on-ramp and allow enough room with respect to other vehicles so that you can do a 1/2 -3/4 throttle acceleration up to freeway speed.
  
• When you have accelerated up to around 60 mph and have safely merged in to the flow of traffic, stay in the slow lane and maintain a steady speed of 55 to 60 mph. Be very careful to keep the vehicle speed between 55 mph and 60 mph, use the Cruise Control if necessary. Do this 55-60 mph cruise for a distance 4-5 miles.
  
• Then find a nice long off ramp to exit from the freeway. As you exit, take you foot of the accelerator and let the vehicle coast down under its own power to a stop as you complete your exit from the freeway. Do NOT use the foot brake and do NOT shift gears until the very end of this 'coast down' phase.
  

      Step Four, more city driving

• After you have completed the freeway trip, drive through some more city streets. This is a repeat of the second part of step two.
  
• Go up to about 35-40 mph and at the normal city speed of 25 mph a few times before slowing down to stop. Don't roll through the stop, be sure the car is really stopped, just like you are in driving school. Accelerate from each stop in a normal fashion not overly conservative but not like a drag race either.
• Pull in to a parking place and let the engine idle for 1-2 minutes and then shut it off.

      Step Four, have your Readiness Monitors checked and verified

• Drive your vehicle to your regular shop and have them check your Readiness Monitors. They should do this as a courtesy and for no charge.
  
• If all your Monitors are 'Ready' and there are no codes set, then your vehicle has been properly repaired and it's ready for an Emissions Inspection and/or for normal driving.
  
• If your Monitors are not 'Ready' then proceed to this next article.
• Drive Cycle Issues

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