Patent ID: 8346424

Claim:
A method of monitoring an onboard diagnostic system for a plug-in hybrid electric vehicle, the method comprising: defining an in-use performance ratio to be equal to a saved numerator divided by a saved denominator; monitoring a vehicle-on status of the vehicle to determine when the vehicle is turned on to define a drive cycle; monitoring an engine-on status of an internal combustion engine of the vehicle to determine when the internal combustion engine is fueled during each drive cycle to define an engine-on cycle; measuring a period of time the vehicle is turned on after the internal combustion engine is fueled for each drive cycle; measuring a period of time the vehicle is turned on and operating at a speed equal to zero miles per hour (0 mph) after the internal combustion engine is fueled for each drive cycle; measuring a period of time the vehicle is turned on and operating at a speed greater than a pre-determined speed after the internal combustion engine is fueled for each drive cycle; incrementing the saved denominator to define a current denominator for each drive cycle when the vehicle has been turned on for a period of time greater than a pre-defined minimum total time criteria after the internal combustion engine is fueled, the vehicle has been operating at a speed equal to zero miles per hour (0 mph) for a pre-defined minimum idle criteria after the internal combustion engine is fueled, and the vehicle has been operating at a speed greater than the pre-determined speed for a pre-defined minimum time criteria after the internal combustion engine is fueled; incrementing the saved numerator to define a current numerator for each drive cycle when the onboard diagnostic system successfully completes a diagnostic check; and calculating a current in-use performance ratio after each identified drive cycle by dividing the current numerator by the current denominator when the saved numerator has been incremented during the drive cycle, or by dividing the saved numerator by the current denominator when the saved numerator has not been incremented during the drive cycle.