OBDII Emission Monitors


- An important part of the vehicle's OBDII system are the Emission´s Monitors, they are indicators used to find out if all the emission components have been evaluated by the OBDII system. These monitors periodically process tests on specific systems and components to ensure they are running in the allow limits.

- Currently, there are 11 Emission 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 each vehicle depends on the emission control strategy of vehicle engine manufacturers.

Continuous Monitoring Systems


- Some of the components or systems of a vehicle are continuously checked 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:

  • Lack of Power (Misfires).
  • Fuel system.
  • Comprehensive component monitoring.

- Once the vehicle is started up, the OBDII system is continuously checking the above-mentioned components, monitoring: key engine sensors, engine misfires, and fuel demands.


Non-Continuous Monitoring Systems



- Non-continuous monitoring is the one you do in a driving cycle, it means that it requires the vehicle to be operating under specific conditions before the monitoring is ready. This are the monitoring:


Catalyst Efficiency Monitor

- This strategy monitors the two heated oxygen sensors. Compare the concentration of O2 before and after the catalyst. This program knows that most of the O2 entering the catalyst has to be used inside of it in the oxidation phase. It checks if the catalyst is working properly.


Spark Fault Monitor

- Here, crankshaft velocity fluctuations are monitored and it is determined if a misfire occurred by these speed variations between each of the crankshaft teeth. This strategy is so precise that it can determine the severity of the failure and the cylinder that is failing.


Fuel System Monitor

- This is one of the most important monitors and receives high priority. Monitors the delivery of fuel needed (short and long term fuel adjustment). If a little or too much fuel is delivered over a predetermined period of time during a driving cycle, a fault code is recorded.


Oxygen Sensor Monitor


Heated Oxygen Sensor Monitor

- When operating conditions allow, fuel injectors are pulsed to a fixed duty cycle and the response time and voltage of each oxygen sensor is monitored.


EGR System Monitor

- This is a passive test who is executed when the driving conditions permit. There are many EGR designs, and monitoring systems. Most of them use available elements in the system such as O2 concentration in the exhaust or fluctuations in the intake Pressure.


EVAP System Monitor

- The evaporative fuel tank system is an important source of hydrocarbon emissions. OBD2 solved this problem by monitoring the integrity of the entire system seal. The monitoring program has the ability to detect a 1mm hole anywhere in the diameter system!.


- The measurement is made by a modified MAP sensor that is located in the purge line between the activated carbon tank and the purge valve.

Secondary Air System Monitor

- The OBD2 requirements dictate that this system should be monitored. It verifies that when injecting air before the first O2 sensor, the mixture varies and the O2 sensors detect it


Status of the Emisson Monitor OBDII

- OBDII systems must indicate, in any case, whether the vehicle's PCM monitor system has completed the tests on each component. The components that have been tested will be reported as "READY" or "COMPLETE", it means that they have been tested by the OBDII system. The purpose of recording the status of Emission monitors is to allow inspections to determine if the vehicle's OBDII system has checked all components and/or systems.

- The engine and transmission module (PCM) sets the monitor to "READY" or "COMPLETE" after an appropriate driving cycle has been performed. The driving cycle that enables a monitor and activates the emission codes to "READY" varies for each monitor individually. Once a monitor is set to "READY" or "COMPLETE", it will remain in that state. Some factors, including deleting fault codes (DTCs) with a Scanner or a battery disconnection, can cause the emission monitors to be set to "NOT READY". Since the 3 continuous monitors are constantly being evaluated they will be in "READY" status at all times. If the verification of a non-continuous monitor supported, has not been completed, the status of the monitor will be indicated as "NOT COMPLETE" or "NOT READY".

- In order for the OBD monitor system to be ready, the vehicle should be driven under a variety of normal conditions. These conditions may include a mixture of road driving, stops and marches, driving by city, and at least some night driving. For specific information about how to get emissions monitors ready, refer to your vehicle's manual.


Compartir en Facebook  Compartir en Twitter  Compartir en Google+