The OBDII Drive Cycle
Drive cycles vary among manufacturers. The OBDII system sets a fault code and illuminates the check engine light if emissions exceed 1.5 times the emissions standards.
The OBDII monitors are rendered not ready to monitor vehicle emissions when the power to the engine control module is disconnected. Perform the recommended drive cycle to set the OBD II system monitors. There are several different OBDII readiness monitors.
The misfire, fuel trim, and comprehensive monitors are continuous monitors; others require a drive cycle. After meeting certain conditions, the monitor will report "ready."
For example, the system monitors the heated oxygen sensors during a cold start. 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.
OBDII Readiness Monitors
- Catalyst Monitor
- EGR System Monitor
- Fuel System Monitor
- Misfire Monitor
- Oxygen System Monitor
- Secondary Air Monitor
The system monitors several systems and may even test systems like the evaporative emissions while the vehicle is at rest. Manufacturers also publish drive cycles to set specific monitors like the catalyst monitor to monitor catalytic converter efficiency.