On-Board Diagnostic Tests
ON-BOARD DIAGNOSTIC TESTSA diagnostic test is a series of steps which has a beginning and end, the result of which is a pass or fail reported to the Diagnostic Executive. When a diagnostic test reports a pass result, the diagnostic executive records:
1. The diagnostic test has completed since the last ignition cycle.
2. The diagnostic test has passed during the current ignition cycle.
3. That the fault identified by the diagnostic test is not currently active.
When a diagnostic test reports a fail result, the diagnostic executive records:
1. The diagnostic test has completed since the last ignition cycle.
2. That the fault identified by the diagnostic test is currently active.
3. That the fault has been active during this ignition cycle.
4. The operating conditions at the time of the failure.
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 trip vary as they may involve items of an unrelated nature; driving style, length of trip, ambient temperature, etc. Some diagnostic tests run only once per trip, (as in the case of catalyst monitor) while others run continuously (as with misfire and fuel system monitors). If the proper enabling conditions are not met during that ignition cycle, the test may not complete or run at all.
In addition, the execution of diagnostic tests may also be bound by conditions which must comprehend a "Warm-up cycle." A "Warm-up cycle" consists of engine start-up and vehicle operation such that the coolant temperature has risen 5°C (4O°F) from start-up and reached a minimum temperature of 71°C (160°F). If this condition is not met during the specific ignition cycle, some diagnostic tests may not run. Refer to specific Diagnostic Trouble Code (DTC) chart for DTC criteria.