Here are step-by-step instructions on how to perform a basic, yet very
effective,
Drive Cycle that will complete the
readiness monitors for your vehicle's emissions control system. The
Drive Cycle is one of the methods used by the
powertrain control module (PCM) to determine whether an
emissions system repair was properly
performed.
A Drive Cycle is a special test drive that duplicates the
scenario of a person starting her car and making a short freeway trip, as if
she were driving to work. While the Drive Cycle test is going, the engine
computer runs little tests or "readiness monitors" 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
powertrain control module (PCM). The 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 PCM will run a series of self-tests to determine whether or not the
repair actually corrected the problem and if the various emissions systems
are running properly. If they are, they can now properly minimize the
emissions released into the atmosphere from the vehicle's operation.
This process was designed to prevent a vehicle from slipping through an
emissions test with a known problem. Until 1996, a common tactic was to turn
off the
Check Engine Light by clearing the code just before an emissions test,
without performing the proper repair. The Drive Cycle and Emissions
Readiness Monitors have, for the most part, stopped this unethical tactic.
How to Perform a Basic Drive Cycle
Step One: How to Prepare Your Vehicle
- Have the fuel tank between 30 and 70 percent full. Some 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, all of
the memory from the
powertrain control module (PCM) is erased, which includes the data
that accurately tracks the results from various stages of the Drive
Cycle. Also, if the battery is weak or undercharged, some of the most
important tests will never run.
- The vehicle must sit overnight, or for at least eight hours, in an
environment that is less than 90＜ F. The engine temperature needs to
match the air temperature in order to establish an accurate baseline for
the testing. If the outside temperature is over 90＜ F, the fuel is 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 because many of the onboard
computers "boot up" when the keys are in the ignition. Also, many of the
onboard computers still run until all of 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 two to three minutes in Park
or Neutral. While it is idling, turn on the head lights,
heater/defroster, and rear defroster for a three to five 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 at
about 25 mph. Go up to about 35 to 40 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 learned in driving school. Accelerate from each
stop in a normal fashion！not overly conservative, but not like you are
competing in 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 to 3/4 throttle acceleration up
to freeway speed.
- When you have accelerated up to around 60 mph and have safely merged
into the flow of traffic, stay in the slow lane and maintain a steady
speed of 55 to 60 mph for a minimum of five miles. Please use the cruise
control to help you maintain speed.
- Find a nice, long off ramp to exit from the freeway. As you exit,
take your foot off of the accelerator and let the vehicle coast down
until it stops under its own power 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 the city
streets for a repeat of the second part of Step Two.
- Go up to about 35 to 40 mph a few times and then maintain a city
speed of 25 mph before slowing down to stop. Again, don't roll through
the stop and make sure to accelerate normally.
- Pull in to a parking place and let the engine idle for one to two
minutes and then shut it off.
Step Five: Wave your Readiness Monitors Checked and Verified
- Drive your vehicle to your regular shop and have them re-check your
readiness monitors, present codes, and pending codes. They should do
this as a courtesy and for free.
- If all of your monitors are "ready" and there are no present or
pending codes, then your vehicle has been properly repaired and is ready
for an emissions inspection and for normal driving.
- If your monitors are not ready, please
click
here for more information.