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4
2.4 OBD II Readiness Monitors
An important part of a vehicle’s OBD II system is the Readiness
Monitors, which are indicators used to find out if all of the emissions
components have been evaluated by the OBD II system. They are
running periodic tests on specific systems and components to ensure
that they are performing within allowable limits.
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 OBD II 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 OBD II 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. For different ignition
type engines, the available monitors are different too.
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