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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 fi nd out if all of the emissions components have been evaluated by the
OBD II system. They are running periodic tests on specifi c systems and components to
ensure that they are performing within allowable limits.
Currently, there are eleven OBD II I Readiness Monitors (or I/M Monitors) defi ned by the
U.S. Environmental Protection Agency (EPA). Not all monitors are supported in every
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 specifi c vehicle
operating conditions. The continuously monitored components listed below are always
ready:
1. Misfi re
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 misfi re, and monitoring
fuel demands.
Non-Continuous Monitors -- - Unlike the continuous monitors, many emissions and engine
system components require the vehicle to be operated under specifi c conditions before the
monitor is ready. These monitors are termed noncontinuous monitors and are listed below:
1) EGR System
2) O2 Sensors
3) Catalyst
4) Evaporative System
5) O2 Sensor Heater
6) Secondary air Injection
7) Heated Catalyst
8) A/C system
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