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Currently, there are eleven OBD II Readiness Monitors (or I/M Monitors)
defined by the U.S. Environmental Protection Agency (EPA). Not all
monitors are supported by all vehicles and the exact number of monitors in
any vehicle depends on the motor vehicle manufacturer’s emissions control
strategy. Continuous Monitors -- Some of the vehicle components or
systems are continuously tested by the vehicle’s OBDII system, while
others are tested only under specific vehicle operating conditions. The
continuously monitored components listed below are always ready:
1. Misfire
2. Fuel System
3. Comprehensive Components (CCM)
Once the vehicle is running, the OBDII system is continuously checking the
above components, monitoring key engine sensors, watching for engine
misfire, and monitoring fuel demands. Non--Continuous Monitors -- Unlike
the continuous monitors, many emissions and engine system components
require the vehicle to be operated under specific conditions before the
monitor is ready. These monitors are termed non-continuous monitors and
are listed below:
1. EGR System 5. O2 Sensor Heater
2. O2 Sensors 6. Secondary air
3. Catalyst 7. Heated Catalyst
4. Evaporative System 8. A/C system
OBD II Monitor Readiness Status
OBDII systems must indicate whether or not the vehicle’s PCM’s monitor
system has completed testing on each component. Components that have
been tested will be reported as “Ready”, or “Complete”, meaning they have
been tested by the OBDII system. The purpose of recording readiness
status is to allow inspectors to determine if the vehicle’s OBDII system has
tested all the components and/or systems. mThe powertrain control module
(PCM) sets a monitor to “Ready” or “Complete” after an appropriate drive
cycle has been performed. The drive cycle that enables a monitor and sets
readiness codes to “ready” varies for each individual monitor. Once a
monitor is set as “Ready” or “Complete”, it will remain in this state.
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