It depends on the vehicle. There are specific items that must be met before many monitors will run. The problem there is that many of the lower end code readers cannot read all of the codes in a vehicles system and some of those will block other tests from running. In the case of the EVAP system they have different methods of running the tests depending on the vehicle. For most driving distances have nothing to do with the EVAP running.
For the 2002 Buick in this question the EVAP cycle is as follows -
Barometric pressure must be more than 65 kPa.
Engine coolant temperature must be less than 150°F.
Fuel level is between 1/4 and 3/4 tank.
Battery voltage is between 10-18 volts.
Connect a scan tool and verify that no codes are pending or present. Run the service bay EVAP test. If no codes, Start the engine, let it idle no more than 3 minutes, Drive the vehicle at part throttle and 45 mph. Until it reaches operating temperature.
Once the vehicle reaches full operating temperature drive an additional 3-5 minutes and verify if the monitor has set to yes.
If it has not then scan for any codes that may inhibit the test from completing.
For instance say you do all of the above but the car has a pending code for EVAP that doesn't turn on the light because it is a type B code (requires 2 consecutive failures before it will turn on the light) That will cause the test to abort. Now the car has to run another drive cycle as above before it will disregard that code and run the EVAP again. That means it has to set long enough for the coolant to drop below 150°F. Then it will run the test again.
On other cars there is no driving required, they actually run the test as soon as the engine is started and the coolant and intake air temperature match as well as the fuel level. Then you also have some that run the EVAP test while the vehicle cools down after it is shut off after being driven.
Thursday, November 14th, 2019 AT 5:43 PM
