OBD II Drive Cycle
Drive cycles vary among manufacturers. The OBD II system will set a fault code and illuminate the check engine light if emissions exceed 1.5 times the emissions standards. Disconnecting power from the engine control module will render the OBD II monitors not ready to monitor vehicle emissions. Perform the recommended drive cycle to assure 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. This and other systems are monitored continuously. Manufacturers’ also publish drive cycles to set specific monitors like the catalyst monitor monitoring catalytic converter efficiency.