I/M (Inspection & Maintenance) Monitors test the operation of emission-related systems or components and detect out-of-range values. The vehicle may have to be operated under certain conditions to complete an I/M Monitor test.

Currently, there are eleven I/M Monitors defined by the U.S. Environmental Protection Agency (EPA). Not all monitors are supported by all vehicles. These I/M Monitors are:

I/M Monitor	Definition
Misfire	Misfire
Fuel Sys	Fuel System
Comprehens	Comprehensive Components
Catalyst	Catalyst
Heated Cat	Heated Catalyst
Evap Sys	Evaporative System
Sec Air	Secondary AIR
A/C Refrig	Air Conditioning Refrigerant
O2 Sensor	Oxygen Sensor
HO2 Sensor	Heated Oxygen Sensor
EGR Sys	Exhaust Gas Recirculation System

• A monitor status of Ready means that the required driving conditions for that monitor have been met and it passed.
• A monitor status of Not Ready means that the required driving conditions for that monitor have not been completed or it did not pass.
• A monitor status of N/A means that the vehicle does not support that monitor.

Several state emission check programs require all I/M Monitors to be in a status of Ready or N/A in order for the vehicle to pass. You can use AutoXray Scan Tools and Code Readers to find out if your vehicle is ready before going to your state emission test.