OBD II Drive Cycle
Drive cycles vary among manufacturers. The OBD II system sets a fault code and illuminates the check engine light if emissions exceed 1.5 times the emissions standards. Whenever power is disconnected from the engine control module, the OBD II monitors are rendered not ready to monitor vehicle emissions. Perform the recommended drive cycle to ensure the OBD II system monitors are set.
Different monitors are set and run under different conditions. During a cold start, the heated oxygen sensors are tested. While accelerating up to 55 mph, the misfire, fuel trim, and purge monitors are enabled. The chart above illustrates some of the monitors and steps involved.
The system monitors several systems and may even test systems like the evaporative emissions while the vehicle is at rest. They are monitored continuously. Manufacturers also publish drive cycles to set specific monitors like the catalyst monitor to monitor catalytic converter efficiency.