OBDII Readiness Monitors

Vehicle Emissions Test

The OBDII monitors are "not ready" to monitor vehicle emissions when the power to the engine control module is disconnected. Perform the recommended drive cycle to set the OBDII monitors and ensure that the monitors are "ready" to monitor vehicle emissions before running an emissions test.

  • Catalyst Monitor READY
  • EGR System Monitor READY
  • Fuel System Monitor READY
  • Misfire Monitor READY
  • Oxygen System Monitor READY
  • Secondary Air Monitor READY

OBDII Drive Cycle

Drive cycles vary among manufacturers. The misfire, fuel trim, and comprehensive monitors are continuous monitors; others require a drive cycle. After meeting certain conditions, the monitor will report "ready."

OBD II Drive Cycle Chart

The chart above illustrates some of the monitors and steps involved. 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.

OBD II Scan Tool

The OBDII system sets a fault code. It illuminates the check engine light if emissions exceed 1.5 times the emissions standards.

Check Engine Light

The system monitors several systems. It may even test systems like the evaporative emissions while the vehicle rests. Manufacturers also publish drive cycles to set specific monitors like the catalyst monitor to monitor catalytic converter efficiency.