First, the drive-cycle criteria may not have been met yet and the monitor isn't finished. Second, a related monitor has issued
a "failed" report to the PCM. An example of this is the oxygen (O2) sensor monitor: If the PCM finds a problem with an O2 sensor, then the related catalyst efficiency monitor cannot run accurately and it will not complete. Once a monitor status has changed to "complete," it will remain that way until it is reset, either by clearing the codes or
by disconnecting the battery. This is also important to know. All monitors may show as "complete" but we don't know how old
the test results are, especially in the case of non-continuous monitors. You also need to understand that a monitor that shows
as "complete" doesn't mean that it didn't detect a failure and the system is OK. A completed monitor only means that all the conditions necessary for it to run its tests have been met and the tests have
been run at least once since being reset. PUTTING IT INTO PRACTICELet's look at a 2000 Jeep Grand Cherokee with a MIL on complaint. Checking the status of the monitors shows some of the monitors
are "not ready." See Figure 2. 
Figure 5 Here's the information. Now it's up to us to decide the best way to use it.
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From this we can already begin our data gathering for diagnosis. We know that someone has cleared codes and information that
may have been stored because there are monitors in a "not ready" status. A valuable resource to use is your service information
system for just that – information.
By looking under "Theory and Operation," you can find information on what conditions are needed for these missing monitors
to complete. At this point, it may be because a fault is identified in another monitor and that this fault is preventing the
others from running. Another possibility is that the driving conditions needed by the uncompleted monitors have not yet been
met. The next clue in this example is that the MIL is illuminated. That tells us that a fault has been de-tected at least once
(if it is a one-trip code) because the codes and data were cleared and there have not been the three successive monitors run
without the failure the PCM needs to turn off the MIL. Yet another is in the monitor list. Notice that the oxygen sensor and catalyst efficiency monitors have not completed. Neither
has the EVAP monitor. What does that tell you? What do these monitors have in common? The oxygen sensor monitor has to complete
before the catalyst monitor can complete. But what needs to happen before the oxygen sensor monitor can run? The oxygen sensor heater monitor does, and although that monitor also shows as incomplete, it doesn't mean the PCM didn't
find a fault. As a part of some monitor strategies, a failed individual test may suspend completion of the monitor. Let's
go to Mode $03 and find out. Once you have the codes, resist the urge to clear them. There are still a few more questions
for the PCM. Are there any other faults the PCM found that we haven't been told about yet? Mode $07 may tell us, so let's check for pending
codes and see what's there. See Figure 3. How about the conditions that were present at the time the code was recorded? Mode
$02 has this information; it is more commonly known as "Freeze Frame Data." See Figure 4.
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