It means cars today with all their computers are WAY too complicated for do-it-yourselfers to try to fix. Your vehicle runs a series of self tests on the emissions system at periodic intervals. A drive cycle is a series of events that must occur while you're driving the vehicle. Some examples of these events could be:
engine must be warmed up.
fuel level cannot be more than 3/4 full.
must have a period of at least half-throttle acceleration.
must remain in third or fourth gear for at least five minutes.
must not touch the brake pedal.
must not completely release the gas pedal.
must have at least a five second long period of coasting without touching the brake or gas pedals.
These are just possible examples of what are included in a drive cycle. Often the mechanic will have to drive a customer's car while forcing these conditions to occur. Not all monitors run at the same time, and most of the time you won't even know when they do run. In one common monitor the engine computer will energize the purge solenoid to open a path for stored fuel vapor to be drawn from the charcoal canister into the engine where it is burned. The computer expects to see an unusually rich condition detected by the oxygen sensor. It won't run that test if a diagnostic fault code related to the O2 sensor is stored in memory since the results would be meaningless.
Many states no longer do emissions testing. Instead, they just check to see if the monitors have run and passed. If you do a lot of short trip or city driving, there are some monitors that will never run. You should still be able to read the diagnostic fault codes.
caradiodoc
Dec 26, 2009 at 2:33 AM
