Leave the car sit for about six to eight hours. (or overnight) The temperature when you go to start the car has to be 39f or higher or some of the evap tests won't run. Look for at least 45f if it was very cold overnight so that the vehicle has warmed up a bit before you start. Then follow these instructions as close as possible. Especially the three accelerations and then the two minute idle, that preps the catalyst for testing and the test runs at idle.
Start the engine, and drive at low highway speeds for about 4 miles. (30-45mph) You can have some stops and idle periods during this time as in local city driving.
Next accelerate to 55-70mph for at least five miles, maintain a constant speed.
Slow to a stop. The drive again at the 30-45mph range for two miles. Once that is done, without stopping or hitting the brakes, accelerate to 45-50mph and then let the car slow down as you count to 20 seconds. (1-1000, 2-1000 etc). Speed back up 1/4 throttle to 45-50mph and decel for another twenty seconds. Do that a third time, only this time be prepared to pull off the road where you can stop and idle in gear for about thirty seconds, then put the transmission in park and idle for 120 seconds more. Now drive it back home or to the shop normally. If the tests didn't run and complete have someone pull trouble codes, especially the Mode7 which are called pending codes. If one of the two trip monitors (tests) ran and failed it will generate a pending code, which would mature into a check engine light and a full code the next time that it fails. HTH.
