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2.4 OBD II Readiness Monitors
An important part of a vehicle’s OBDII system are the Readiness
Monitors, which are indicators used to find out if all of the emissions
components have been evaluated by the OBD II system. Periodic
tests are run on specific systems and components to ensure that they
are performing within allowable limits.
Currently, there are eleven known OBD II Readiness Monitors (or I/M
Monitors). 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 Monitoring (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
2. O2 Sensors
3. Catalyst
4. Evaporative System
5. O2 Sensor Heater
6. Secondary Air
7. Heated Catalyst
8. A/C system
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