Originally Posted By: MalfunctionProne
I think they want it to run a certain amount of time, as they want to be satisfied that I am not trying to "fool" the scan test.
That's not how it works. OBD-II cannot be "fooled" the way previous OBD systems could be. The monitors are either ready or they are not. OBD-II tests are run by the computer in the background while you drive. You are never even aware of it.
I think the period of engine-idle is used to check for exhaust leaks, etc. Stuff you wouldn't be able to tell unless the engine is running.
Originally Posted By: MalfunctionProne
Not sure what isn't "ready" about it.
Here's a partial screen-shot from a certain OBD-II diagnostics program. This screen-shot is from the program's built-in simulation, since I didn't have the laptop actually connected to any car at the time.
Note that three tests are green. The green means that the OBD-II computer has successfully run and complete the tests for that monitor, and the system passed the test. These monitors are therefore reported "Ready".
The two red monitors are problem areas. The OBD-II computer has determined that both tests either did not run, or ran and failed. Those monitors are therefore reported "Not Ready".
Note that the two Oxygen Sensor tests are not supported by the simulated car's computer. Which is weird since in real-life they would definitely be supported by any OBD-II vehicle.