The OBD-II diagnostic system continually monitors for misfire and fuel system faults. It also performs a functional test on the catalyst, EGR system, and oxygen sensors once during every driving cycle or "trip ". Certain driving conditions must be encountered before these systems can be confirmed as operating normally. For example, the engine must be fully warmed up, throttle angle must have exceeded a specified angle, the engine must have achieved a specified load, and so on.
In the event that these driving conditions have not been met, the ECM will not have completed its "readiness test", and is not capable of displaying supported test data. Under these conditions, the scan tool will display a message indicating that "not all supported readiness tests are complete", warning the operator that this test data is not available.
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