Method of monitoring in-use performance ratios of onboard diagnostic systems for plug-in hybrid electric vehicles

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;
• 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;
• comparing the current in-use performance ratio to a minimum performance ratio floor to determine if the current in-use performance ratio is greater than the minimum performance ratio floor or less than the minimum performance ratio floor;
• maintaining operation of the internal combustion engine during the next engine-on cycle for a time sufficient to allow the onboard diagnostic system to complete a diagnostic check when the current in-use performance ratio is less than the minimum performance ratio floor to allow the onboard diagnostic system to successfully complete the diagnostic check to allow the saved numerator to increment.
• defining a denominator floor ratio equal to the current denominator divided by a verification denominator;
• and
• incrementing the verification denominator after each identified drive cycle that includes the vehicle turned on for a period of time greater than the pre-defined minimum total time criteria, the vehicle operating at a speed equal to zero miles per hour (0 mph) for the pre-defined minimum idle criteria, the vehicle operating at a speed greater than the pre-determined speed for the pre-defined minimum time criteria, and the internal combustion engine turned during the identified drive cycle.