2.4 OBD II Readiness Monitors
An important part of a vehicle’s OBDII system is the Readiness monitors, which are
indicators used to nd out if all of the emissions components have been evaluated by the
OBD II system. They are running periodic tests on specic systems and components to
ensure that they are performing within allowable limits.
Currently, there are eleven OBD II Readiness Monitors (or I/M Monitors) dened 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 specic vehicle
operating conditions. The continuously monitored components listed below are always
ready:
1. Misre
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 misre, and
monitoring fuel demands.
Non--Continuous Monitors -- Unlike the continuous monitors, many emissions and
engine system components require the vehicle to be operated under specic 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
2.5 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
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