On Board Diagnostic Tests

A diagnostic test is a series of steps which has a beginning and an end. The result of this diagnostic test is a pass or fail that is reported to the Diagnostic Executive. When a diagnostic test reports a pass result, the Diagnostic Executive records the following data:
^ The diagnostic test has completed since the last ignition cycle.
^ The diagnostic test has passed during the current ignition cycle.
^ The fault that is identified by the diagnostic test is not currently active.

When a diagnostic test reports a fail result, the Diagnostic Executive records the following data:
^ The diagnostic test has completed since the last ignition.
^ The fault that is identified by the diagnostic test is currently active.
^ The fault has been active during this ignition cycle.
^ The operating conditions at the time of the failure

Trip
The ability for a diagnostic test to run depends largely upon whether or not a Trip has been completed. A Trip for a particular diagnostic is defined as vehicle operation, followed by an engine off period of duration and driving mode such that any particular diagnostic test has had sufficient time to complete at least once. The requirements for trips vary as the trips may involve items of an unrelated nature, such as the driving style, the length of trip, the ambient temperature, etc. Some diagnostic tests run only once per trip (e.g. catalyst monitor) while other diagnostic tests run continuously (e.g. misfire and fuel system monitors). If the proper enabling conditions are not met during that ignition cycle, the tests may not be complete or the test may not have run.

Warm-up Cycle
In addition, the execution of the diagnostic tests may also be bound by the conditions which must comprehend a Warm-up cycle. A Warm-up cycle consists of an engine start-up and a vehicle operation such that the coolant temperature has risen greater than 4°C (40°F) from the start-up temperature, and reached a minimum temperature of 160°F If this condition is not met during the ignition cycle, the diagnostic may not run.