For most OBD II strategies, the same malfunction must occur on two driving events to illuminate the MIL. This “double” detection ensures a malfunction exists before alerting the owner. The first time a malfunction is detected, a “pending” fault code, which identifies the failing component or system, is stored in the onboard computer. If the same malfunction is again detected the next time the vehicle is operated, the MIL is illuminated, and a “confirmed” fault code is stored. When the MIL is illuminated (alerting the vehicle operator to a problem), and a vehicle is brought in for service, a technician uses the “confirmed” fault code to determine what system or component has failed. A “pending” fault code, however, can be used by service technicians to help diagnose intermittent problems and verify that repairs were successful. In these instances, a technician can use the “pending” fault code as a quicker, earlier warning of a suspected (but as yet unconfirmed) problem.

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