OBD II Terminology

In order to make sense out of the rest of this section you must understand just what each of the following terms or concepts mean, as they will appear on almost every article.

ENABLE CRITERIA
Enable criteria are the operating conditions which must be met before a particular diagnostic test will run. There are almost as many different "enable criteria" as there are fault codes, the objective being to make sure that each circuit or component is tested under the proper conditions. For example, it would not make any sense to try to monitor the efficiency of a cold catalyst which has not had time to reach operating temperature. Some typical catalyst monitor enabling criteria are shown below.

^ Coolant temperature above 140°F (60°C).
^ Vehicle speed between 20 & 60 mph (30-100 km/h).
^ Fuel system operating in closed loop.
^ Throttle open
^ All above conditions have been met for more than 120 seconds
^ More than 3 minutes have passed since starting

WARM-UP CYCLE
In order for a warm-up cycle to take place the following things must happen after starting the engine:

^ Coolant temperature must increase by at least 40°F (22°C)
^ The final temperature must reach a minimum of 160°F (71°C)

DRIVING CYCLE
One driving cycle has occurred when the following condition is met:

^ The engine has been started and shutoff

TRIP
A trip has occurred when:

^ The engine has been started
^ The vehicle has been driven in such a way that ALL components and functions covered by OBD II have been monitored

NOTE: For most people a "trip" is what happens during the time between starting the car and turning it off again, regard less if they have driven for five minutes or five hours. In OBD II terms, a trip has not occurred until every single enable criteria for each diagnostic procedure has been met and every test has had a chance to pass or fail. Depending on local driving conditions, it may take many "trips" to work or the corner store before you have completed one official OBD II trip.

SIMILAR DRIVING CONDITIONS
Some faults will not illuminate the MIL, turn it off or erase a DTC until the test has been failed (or passed) a given number of times under "similar" driving conditions. Similar driving conditions are when:

^ Engine speed is within ±375 RPM
^ Engine load is within ±10%
^ Coolant temperature is either higher or lower than 160°F (71°C) depending on which side of this breakpoint the original fault occurred.