Vehicle Emissions Testing FAQs

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for the Illinois Vehicle Emissions Testing Program

Frequently Asked Questions (FAQs)

Questions about Vehicle Emissions Testing

What are your hours of operation for emissions testing?

Testing hours are: Monday through Friday from 8:00 AM to 6:00 PM and Saturday from 7:30 AM to 1:00 PM. Testing stations are closed on Sundays and State Holidays. For a list of State Holidays, click here.

Can vehicles with a device connected to the OBD DLC be tested?

Any device plugged into a vehicle’s On-Board Diagnostics (OBD) Data Link Connector (DLC), such as an insurance dongle, tracking device, GPS tracker, radio, gauges, scantool, etc. will need to be removed by the motorist prior to testing. Vehicles equipped with BAIID devices connected to the DLC will be tested without removing the device.

Why does the vehicle emissions test program exist?

The goal of the Illinois Vehicle Emissions Testing Program is to improve air quality and public health. The federal Clean Air Act Amendment of 1990 requires emissions testing programs in large, metropolitan areas which do not meet certain federal air quality standards. Although Illinois has made significant strides to clean its air since the Amendments took effect, levels of air pollution in Chicago and the Metro-East St. Louis areas still exceed these standards.

Why is it important to reduce emissions?

Motor vehicle emissions, including carbon monoxide, nitrogen oxide and hydrocarbon, are a significant source of pollution. Carbon monoxide is a colorless, odorless gas that may cause dizziness, difficulty in breathing and death. Hydrocarbon and nitrogen oxide combine with sunlight to form ground level ozone (smog). Ozone can aggravate health problems for people with heart disease and breathing-related diseases such as asthma and emphysema. It can be especially harmful to children and the elderly.

What vehicles are subject to vehicle emissions inspections?

Generally, most 1996 and newer gasoline-powered passenger vehicles are subject to testing after they are four (4) years old. Diesel-powered vehicles, vehicles powered exclusively by electricity, and certain other vehicles are not required to test. Click here to see the full list of vehicles not subject to testing.

Why is my vehicle being tested?

Vehicles are tested to verify that the vehicle's emissions control systems are performing properly. Vehicle emissions testing programs are designed to identify vehicles that need to be repaired to meet emissions standards.

What kind of test is used?

An On-Board Diagnostics (OBD) test is used for 1996 and newer passenger cars and light-duty trucks (including vans, sport utility vehicles and hybrids).

Where can I take my vehicle for testing?

Click here for a complete list of Testing Stations

How often will my vehicle need to be tested?

Vehicles need to be tested when they are four (4) years old. Even model-year vehicles are tested during even years and odd model-year vehicles are tested in odd years. For example, a 2009 vehicle should be tested first in 2013, and thereafter in 2015, 2017, etc. In certain cases, a vehicle may need to be inspected if it was not in compliance when acquired by a new owner, or when the vehicle is newly registered in a test area.

Why doesn't this program test diesel-powered vehicles?

The federal Clean Air Act does not require the inclusion of diesel-powered vehicles in emissions testing programs. However, the State of Illinois has implemented a program to inspect certain heavy-duty diesel- powered trucks over 16,000 pounds in ozone non-attainment areas. This program is administered by the Illinois Department of Transportation.

Does this program test heavy-duty vehicles?

Vehicle emissions testing is required on all 2007 or newer heavy-duty vehicles with a manufacturer's gross vehicle weight rating (GVWR) between 8,501 and 14,000 pounds.

Why aren't newer vehicles given an exhaust and gas cap test?

OBD testing has replaced exhaust and gas cap testing on 1996 and newer vehicles equipped with standardized OBD systems. The OBD systems continually monitor the operation of the vehicle's emissions control system, and when it detects an emissions-related problem an identifying code is stored on the vehicle's on-board computer. When the OBD test is performed, these codes (Diagnostic Trouble Codes (DTCs)) are reported, retrieved and communicated.

What happens if my vehicle fails the test?

If your vehicle fails the OBD test, the inspector will give you a Vehicle Inspection Report (VIR) containing detailed test results, a condensed version of the Repair Shop Report (RSR) that contains a list of repair facilities within a fifteen (15) mile radius, along with additional information. A full version of the RSR is available online here. It provides a list of all known repair shops and relevant information about them.

The inspector will also provide you with a Repair Data Form (RDF). A failing vehicle must be repaired then return to a station for a retest. The Illinois EPA recommends that repairs be made by a technician who is trained and experienced in emissions diagnosis and repair. The repair technician should complete and submit the RDF for you online. If the repair technician does not submit the RDF for you, you must bring it with you at the time of your retest.

How can I qualify for a waiver?

Effective January 1, 2025, the minimum expenditure toward emissions related repairs will increase from $1,111 to $1,146. Applications submitted on or after January 1, 2025, must satisfy the $1,146 minimum requirement.

A repair waiver may be issued if all of the following requirements are met:

The vehicle has been tested at least twice and has failed to comply with emissions standards.
All emissions control devices are present and appear to be properly connected and operating.
The Malfunction Indicator Lamp/Light (MIL) is functioning properly.
A minimum of $1,111 in emissions-related repairs (excluding tampering-related repairs) have been made to the vehicle.
Evidence of the repairs is presented, consisting of receipts dated not more than 30 days prior to the test eligibility date that identify the vehicle by VIN.
The repairs were performed by a recognized repair technician.
All eligible emissions-related warranty repairs and adjustments have been performed pursuant to Section 207 of the Clean Air Act (42 USC 7541).
The vehicle owner is present or the Repair Waiver Application is properly completed.

Click here for more information about repair waivers and to access the Repair Waiver Application.

Why was my vehicle rejected?

Vehicles can be rejected from the test lanes for a variety of reasons. The most common reasons for rejection include: the OBD monitors were not ready; the Repair Data Form (RDF) was not properly completed; the vehicle was not subject to testing; the wrong vehicle was brought in for testing; and the vehicle was brought in too early. Rejects do not count as tests. Use this link to find out more about why vehicles can be rejected.

No longer own vehicle

You must inform the Illinois Secretary of State that you no longer own the vehicle. Once the Secretary of State has updated the vehicle registration information, you will no longer receive test notices. You may notify the Secretary of State in person at an SOS facility, or by completing and mailing the Seller’s Report of Sale form available at: https://www.ilsos.gov/publications/motorist/titlereg.html

Moved and still received test notice

You are required to update the address on your driver’s license and vehicle registration with the Illinois Secretary of State. Once your record is updated, you will only receive an Illinois Vehicle Emissions Test Notice if your new address is located within the testing area. Your drivers license and vehicle registration addresses can be updated by visiting a Secretary of State facility or online at: https://www.ilsos.gov/addrchange/

Questions About Test Notices

Effective November 2016, vehicle emissions test notices will be postcards. An example is shown below.

When can I come in for an emissions test?

The Illinois EPA urges motorists to have their vehicles tested several weeks prior to the expiration of their vehicles’ license plates to allow sufficient time to complete the process. If a vehicle fails the emissions test, it may be necessary to have emissions-related repairs performed to the vehicle, and the vehicle must pass its retest prior to the time its vehicle registration expires. You may come in for a test as early as four (4) months prior to your vehicle’s Test by Date/Registration and License Plate expiration.

Find out if you need to test

Motorists can find out when their vehicle is due for an emissions test by entering the VIN or license plate number into our Vehicle Eligibility Check tool.

Test Eligibility Guidelines:

Most 1996 and newer gasoline-powered passenger vehicles are subject to testing after they are four (4) years old, and typically, even model-year vehicles are tested during even years and odd model-year vehicles are tested in odd years (e.g., 2012 subject vehicles must be tested in 2016 for the first time). The testing month coincides with the expiration date of the vehicle license plate.

Please note that while the vehicle may be tested up to four (4) months prior to license plate expiration, the plate may only be renewed within three (3) months of the expiration date.

License Plate Renewal-Based Enforcement of the Vehicle Emissions Testing Program

Vehicles must pass an emissions test or otherwise comply with the Illinois Vehicle Emissions Inspection Law of 2005 (625 ILCS 5/13C) (“Inspection Law”) before the vehicle’s registration (license plates) can be renewed. A Test Notice is mailed up to four (4) months prior to your vehicle’s license plate expiration to remind you to take your vehicle in for an emissions test. Click here to learn more about renewing your registration at any high capacity drive-thru testing station.

The Secretary of State’s Office mails License Plate Renewal Notices that include a statement as to whether compliance with the Vehicle Emissions Inspection Law is required before a vehicle’s registration can be renewed. The Secretary of State’s Office sends paperless License Plate Renewal Notices via email to individuals who register at https://www.ilsos.gov/greenmail. Electronic notices include a statement as to whether compliance with the Vehicle Emissions Inspection Law is required before a vehicle's registration can be renewed.

Do I need a Test Notice to get my vehicle tested?

No. Inspectors at the testing stations are able to test your vehicle without a notice. If you have received a test notice, you may bring it to the station, and it could slightly expedite your testing experience.

What should I do if my address is incorrect on my vehicle registration or I have moved?

State law requires that you notify the Secretary of State within 10 days of any change of address. As a convenience, change of address forms are available online.

After my vehicle has been tested, do I need to mail anything to the Illinois EPA or the Secretary of State?

No, the test results are automatically recorded on the Illinois EPA database and transmitted to the Secretary of State.

Questions About Ozone

What is ozone?

Gasoline-powered engines produce emissions that form ground-level ozone (smog), a respiratory irritant that can be harmful to humans. Ozone can cause eye and throat irritations and can damage breathing passages, making it difficult for the lungs to work. This pollutant is prevalent in major metropolitan regions, including Chicago and Metro-East St. Louis.

Since the program started in 1986, vehicles have become less polluting, but still contribute significantly to the ozone problem in urban areas. Because vehicles are now equipped with an array of computer-controlled components designed to reduce pollution, enhancements to vehicle emissions testing were necessary to effectively identify excessive emissions.

How is ozone formed?

Near the ground, ozone is formed in a three (3) step process:

Gasoline, paints and solvents evaporate, releasing reactive organic compounds.
Cars and factories burn fossil fuels, releasing nitrogen oxide gases.
Heat and sunlight trigger a chemical reaction between these emissions, transforming them into ozone.

Questions About a Voluntary Test

For a $20 fee, gasoline-powered vehicles that would be testable in the Illinois program may receive a voluntary emissions test. This service may be used by anyone, for example:

An individual considering the purchase of a used vehicle.
An out of state resident whose vehicle is temporarily in Illinois and needs an emissions test to comply with their home state’s requirements.
An auto repair technician to verify repairs and improve customer satisfaction.

The voluntary test is not considered an official test for Illinois vehicles subject to testing.To obtain a voluntary test, a voucher must be purchased at the testing station office prior to entering the test lane. Payment must be made in cash. Checks and credit cards are not accepted.

What to do if Your Vehicle is Rejected

My vehicle was rejected. What does that mean? And what do I do now?

The term “rejected” is used when a vehicle is not able to complete the emissions testing process for any of a variety of reasons. Depending on the reason for rejection, your course of action may range from not having to do anything to having your vehicle repaired in order to have it tested.

What are the reasons my vehicle could be rejected?

The most common reasons for rejection include: the OBD monitors were not ready; the repair form was not properly completed; the vehicle was exempt from testing; the wrong vehicle was brought in for testing; and the vehicle was brought in too early. Rejects cannot be used for the test failure count when applying for a waiver. Click on “Understanding On-Board Diagnostics” for more information about OBD systems, readiness and setting monitors.

Incomplete Repair Data - Vehicles are rejected from their retest when the Repair Data Form (RDF) is not submitted or completed. Complete repair data is required in order to receive a retest. If a Recognized Repair Technician repairs your vehicle, they may enter the repair data online prior to your retest to assist you.
The Vehicle is NOT Subject to Testing - The vehicle is model year 1995 or earlier, is now registered out of the test area, is diesel-powered or is otherwise not subject to testing. Click here to see the full list of vehicles not subject to testing.
The Vehicle Arrived Too Early - The vehicle was brought in for a test more than four (4) months before the license plates expire.
Vehicle Exceeded Four (4) -Test Limit - After failing four (4) tests, no further tests will be allowed unless otherwise authorized.
Vehicle Condition/Safety Issues - Vehicles presented for testing with safety-related defects or modifications can be rejected because they may pose a safety hazard to the inspector or testing station.
Missing Vehicle Identification Number (VIN) - Vehicles are rejected if the VIN cannot be located on the vehicle. These vehicles cannot be tested because inspectors cannot verify that they are testing the correct vehicle.

I repaired my vehicle, now what do I do?

Simply take the vehicle to any of the emissions testing stations for a retest. You should bring all repair receipts and your completed Repair Data Form (RDF) with you.

What if my vehicle fails?

Vehicles that fail an emissions test need to be repaired and retested. We recommend that vehicles be repaired by a Recognized Repair Technician who is trained, experienced and equipped to repair emissions-related failures. The diagnosis and repair of emissions problems has emerged as a specialty in automotive repair and can involve the repair or replacement of multiple components. This can be very challenging -- even to veteran technicians. Statistics indicate most emissions failures cannot be solved by simple tune-ups. When vehicles fail an emissions test, motorists are given several documents to assist them in determining their next steps:

A Vehicle Inspection Report (VIR), that includes a condensed version of the Repair Shop Report (RSR) that contains a list of repair facilities within a fifteen (15) mile radius of the testing station where the test was performed;
A Repair Data Form (RDF);
The VIR provides details about the specific tests performed and the test results, which help a technician diagnose and repair the vehicle.

The RSR is intended to help motorists locate a repair shop to diagnose and repair their vehicle. It includes the repair effectiveness percentage for each of the shops that is based on the success rate of performing emissions-related repairs.

The RDF must be completed and either submitted online by the repair technician or provided to the lane inspector at the testing station before a retest will be performed. It is best if the RDF is submitted online by the repair technician. Vehicles returning for a retest without complete repair data are rejected. It is helpful, and sometimes necessary, that motorists bring itemized receipts for all work that was performed.

Below are answers to commonly asked questions by owners whose vehicles have failed the test.

Why did my vehicle fail the emissions test?

In the case of an OBD test, there are three (3) main reasons for failure:

The OBD system reported an emissions-related malfunction, as indicated by stored diagnostic trouble codes (DTCs) and illumination of the Malfunction Indicator Lamp/Light (“MIL”) (also referred to as the “check engine” light) on the dashboard;
The OBD system is inoperative; or
The Diagnostic Link Connector (“DLC”) is damaged, inaccessible or missing.

I maintain my vehicle and it is running fine, so why did I fail the test?

Generally, emissions control devices have little impact on the drivability of a vehicle. Your vehicle may seem to be operating fine but still have an emissions-related problem. Even the best maintained vehicles might experience these types of failures.

Why can't the emissions station's staff tell me what's wrong with my vehicle?

Personnel at testing stations are qualified to test vehicles for emissions compliance. They are not qualified repair technicians, and they are not authorized to diagnose and repair emissions-related problems.

Personnel at Inspection and Repair Testing Stations (I&Rs) may (or may not) be qualified to diagnose and repair emissions test failures. Motorists are strongly encouraged to refer to and utilize the Repair Shop Report (RSR) to help them select an appropriate repair shop that has demonstrated success in repairing vehicles with emissions-related problems.

Can I do my own repairs?

Yes, but today's modern fuel-injected and computer-controlled vehicles present unique challenges. Emissions failures generally require a high degree of expertise and training to diagnose and repair. The typical vehicle owner could experience considerable difficulty finding and repairing the problem(s) responsible for an emissions failure. It is also important to remember that repairs must be made by a recognized repair technician to qualify towards a repair waiver.

Who are Recognized Repair Technicians?

Illinois law defines a recognized repair technician as “a person professionally engaged in vehicle repair, employed by a going concern whose purpose is vehicle repair, or possessing nationally recognized certification for emissions-related diagnosis and repair” 625 ILCS 5/1-168.5.

Where do I take my vehicle to be repaired?

The Illinois Air Team maintains an online Repair Shop Report (RSR), which lists repair shops and provides a summary of their performance in repairing vehicles with emissions test failures. At the time a vehicle fails the emissions test, the motorist will be provided a condensed list of the closest repair shops to the testing station. The list is provided to assist, however it is not a recommendation. To find a complete list of repair shops or a shop more convenient for you, click here.

Why does my repair shop charge for diagnostic work?

The Vehicle Inspection Report (VIR) gives your technician a list of the diagnostic trouble codes (DTCs) that were stored in your vehicle’s on-board computer at the time of the emissions test. The technician can use this information to help diagnose the problem that caused the vehicle to fail the test. The VIR does not identify what vehicle component(s) are malfunctioning. While this information is helpful to your technician, it does not pinpoint the actual repairs that must be made. The technician uses this information, combined with training, experience and possibly further diagnostic testing, to determine what repairs are needed.

I had repairs made to my vehicle. What do I do?

Ask the technician who performed the repairs to complete the Repair Data Form (RDF), unless the technician or repair shop reports the repair data electronically. If this is a second or third test, the vehicle can be taken to a testing station for a retest. However, if this is a fourth or subsequent test, the retest will need to be approved by station management. The test number can be found in the TEST / FACILITY INFORMATION section of the most recent Vehicle Inspection Report (VIR).

Do I have to go into the station office before I have my vehicle retested?

Not for the first two (2) retests. Additional retests must be approved by an authorized Air Team representative at a high capacity drive-thru testing station.

What is a waiver, and how do I apply?

A waiver allows the owner of a failing vehicle to still be able to renew its registration. A vehicle may qualify for a waiver for the current test cycle if it has failed at least two (2) tests, received a minimum of $1,111 of emissions-related repairs performed by a Recognized Repair Technician and meets all other waiver requirements. Very few vehicles qualify for waivers. Click here for a complete list of waiver requirements.

What if I have a problem with my repair shop?

Illinois law requires repair shops to make specific disclosures to consumers and prohibits certain unlawful practices. For additional information you may contact the Illinois Attorney General's office at 1.800.386.5438 in Chicago, or 1.800.243.0607 in the Metro-East St. Louis area.

Vehicles Not Subject to Testing

The following vehicles are not subject to emissions testing:

Vehicles not subject to registration;
Diesel-powered vehicles and vehicles that are powered exclusively by electricity;
Motorcycles, motor-driven cycles and motorized pedal-cycles;
Antique, expanded-use antique, and custom vehicles, street rods, and vehicles of model year 1967 or before;
Farm vehicles and implements of husbandry;
Vehicles registered in, subject to, and in compliance with the emissions inspection requirements of another state;
Vehicles for which a Junking Certificate has been issued by the Secretary of State pursuant to the Illinois Vehicle Code (625 ILCS 5/3-117);
Implements of warfare owned by the State or federal government;
Vehicles of model year 2006 or earlier with a manufacturer gross vehicle weight rating between 8,501 and 14,000 pounds; and
Vehicles with a manufacturer gross vehicle weight rating greater than 14,000 pounds.

What is Tampering?

Tampering with a vehicle’s emissions control system is prohibited by the Clean Air Act (42 U.S.C. 7522). Emissions controls on vehicles are part of the certified design from the manufacturer to reduce pollution and protect public health.

Tampering could include the removal, bypass, disconnection, damage or in any way rendering ineffective any emissions control device or element of design that has been installed on a vehicle or engine. In summary, this means:

Removing any parts or devices, such as the catalytic converter, oxygen sensor, EGR valve, etc., that will alter the original emissions control equipment configurations on a vehicle;
Disconnecting vacuum lines and electrical or mechanical parts of the emissions control system, such as electrical solenoids, sensors or vacuum activated valves;
Adjusting any element of a vehicle’s emissions control design so that it no longer meets the manufacturer’s specifications;
Installing a replacement part that is not the same in design and function as the part that was originally on the vehicle, such as an incorrect exhaust part; or
Adding a part that was not originally certified on the vehicle (e.g., installing a turbocharger).

Understanding On-Board Diagnostics (OBD)

General Information

The purpose of the OBD system is to ensure the proper operation of the emissions-control system for the life of a vehicle; it accomplishes this by monitoring emissions-related components and systems for deterioration and malfunction. Federal regulations establish requirements for on-board diagnostics (OBD) systems on vehicles.

The OBD system commands or turns on a special warning light on the dashboard called the Malfunction Indicator Lamp/Light (MIL) when it detects a fault that may cause high engine or evaporative emissions. When the MIL is on (or in instances when the MIL is supposed to be illuminated but the bulb is burned out), it means that something is wrong with the emissions system and it requires repair.

If the MIL is flashing, prompt service is required.

Manufacturers cover emissions control systems for varying periods, and your vehicle repairs may be covered by warranty.

Following are typical examples of MILs from vehicle dashboards:

A standard MIL symbol, as shown below, may be displayed, as well:

Frequently Asked Questions

What is OBD and how does it work?

In the early 1980s, vehicle manufacturers began using electronics and on-board computers to control many of the engine control systems, such as fuel and ignition. Accordingly, they had to develop ways to diagnose problems generated by the new electronic hardware found under the hoods of those vehicles and, as a result, the first on-board diagnostics (OBD) systems were introduced. A more sophisticated on-board diagnostics system was eventually developed, and the second-generation on-board diagnostics system became required for most 1996 and newer passenger vehicles, light-duty trucks and similar vehicles.

The engines in today's vehicles are largely electronically controlled. Sensors and actuators detect the operation of specific components (e.g., the oxygen sensor) and activate others (e.g., the fuel injectors) to maintain optimal engine control. An on-board computer, sometimes referred to as a “powertrain control module” (PCM) or an “engine control module” (ECM), controls all of these systems. The on-board computer is capable of monitoring all of the sensors and actuators to determine whether they are working as intended. It can detect a malfunction or deterioration of the various sensors and actuators, usually well before the driver becomes aware of the problem using typical methods such as loss in vehicle performance or drivability. The sensors and actuators, along with the diagnostics software in the on-board computer, make up what is called “the OBD system.”

What is the connection between OBD and vehicle emissions?

OBD is an emissions control system. Older emissions tests that collect or sample the exhaust produced by a vehicle identify vehicles that are already excessive polluters. However, OBD is a shift to pollution prevention. OBD can identify problem(s) with the emissions control system before the vehicle becomes an excessive polluter, allowing time to repair the vehicle before emissions increase. Left un-repaired, further damage can occur and emissions will increase.In most circumstances, the vehicle computer will detect a system problem before the driver notices a drivability problem. Furthermore, OBD can detect problems that may not be noticeable upon visual inspection because many component failures that impact emissions can be electrical or even chemical in nature. By detecting these emissions-related failures and alerting the driver to the need for potential repair, vehicles can be properly repaired before emissions become a problem.

How does OBD inform drivers of problems?

When the OBD system determines that a problem exists, a corresponding “Diagnostic Trouble Code” (DTC) is stored in the computer's memory and a special lamp on the dashboard called a Malfunction Indicator Lamp/Light (MIL) is illuminated. The MIL is reserved for emissions problems only and cannot be used for other failures. Automobiles use a variety of warning lamps to notify drivers of different conditions. In the case of an emissions MIL, either the phrase “Service Engine Soon” or “Check Engine” is used or an engine symbol is displayed. This light, usually yellow in color, serves to inform the driver that a problem has been detected and vehicle service is needed.

When the vehicle is delivered to the repair shop, a service technician can quickly retrieve the stored diagnostic trouble codes (DTCs) from the computer memory of the vehicle. The stored DTCs will help the service technician diagnose and repair the problem. It is important to note that an illuminated MIL is intended to inform the driver of the need for service, NOT the need to immediately stop the vehicle. However, service should be sought as soon as possible. Drivers also may wish to consult a repair shop or their vehicle owner's manual for further guidance.

Why does the Malfunction Indicator Lamp/Light (MIL) blink or flash?

Under certain conditions, the MIL will blink or flash. This indicates a rather severe level of engine misfire. When this occurs, the driver should reduce speed and seek service as soon as possible.Severe engine misfire over only a short period of time can seriously damage emissions control system components, especially the catalytic converter, which is typically the most expensive to replace. Drivers should also consult their vehicle owner's manual for manufacturer specific information.

How can the Malfunction Indicator Lamp/Light (MIL) be turned off?

OBD systems are designed to automatically turn off the MIL if the conditions that caused a problem are no longer present. If the OBD system evaluates a component or system three (3) consecutive times (with some exceptions) and no longer detects the initial problem, the MIL will turn off automatically. As a result, drivers may see the MIL turn on and then turn off. For example, if the gas cap is not properly tightened after refueling, the OBD system can detect the vapor leak that exists from the cap not being completely tightened. If the gas cap is subsequently tightened, the MIL should be extinguished within a few days. This is not an indication of a faulty OBD system. In this example, the OBD system has properly diagnosed the problem and accordingly alerted the driver by illuminating the MIL.

Service technicians can manually turn off the MIL, but if the MIL is turned off manually without correction of the underlying problem that caused the initial MIL illumination, the OBD system will reset the readiness monitors (see “What are readiness monitors?”), and begin the evaluation of the emissions control systems. If the OBD system has not completed the evaluation prior to the emissions test (see “How do readiness monitors affect the automotive repair industry?” and “How can readiness monitors be set?”), the vehicle will be rejected as “not ready”. If the OBD system completes the evaluation and detects the problem again, the MIL will re-illuminate, and the vehicle will fail the emissions test. Therefore, simply turning off the MIL prior to the emissions test, will NOT allow the vehicle to pass.

What are readiness monitors?

1996 and newer vehicles manufactured for sale in the U.S. include software designed to indicate when emissions control systems have a defect that may lead to elevated emissions. These systems include readiness monitors that are used to find out if emissions components have been evaluated. In other words, if all monitors are set to ready, the emissions components have been tested.

These monitors are included in the OBD system so the overall vehicle condition can be easily assessed electronically at an emissions testing station, using a data link connected to the vehicle. To ensure that the data provided to the testing station reflects the actual vehicle condition, the vehicle computer reports whether or not the data in the computer is current and valid. This is referred to as the “readiness” check. The vehicle will be rejected from testing if it fails the readiness check. A vehicle can have up to 12 monitors built into the OBD computer system. The most common monitors are:

Continuous

Misfire
Fuel System
Comprehensive Components

Non-Continuous

Oxygen Sensor
Heat Oxygen Sensor
Catalyst Efficiency
Evaporative Emissions System
EGR System
Secondary Air System
PCV System

How do readiness monitors affect the automotive repair industry?

In the past, technicians routinely cleared codes, either before and/or after performing repairs, as a routine part of the repair process. Clearing codes resets all monitors to a “not ready” status. Some monitors are easily run during normal driving; however, others can take a long time to run. This can cause problems if the vehicle has to return to a testing station for a retest because vehicles cannot be tested if a sufficient number of monitors have not run.

Remember, vehicles are rejected when more than two (2) non-continuous readiness monitors are “not ready” for 1996 to 2000 model year vehicles, or when more than one (1) non-continuous readiness monitor is “not ready” for 2001 and newer model year vehicles. Additionally, the catalyst monitor must be “ready” at the time of any retest after a vehicle failed an initial test for any catalyst code.

By clearing codes during the repair process, shops and technicians may find themselves in situations where the customer takes the vehicle back to an emissions station for a retest after repairs have been made, but the vehicle is rejected at the station because a sufficient number of monitors are not ready. Therefore, shops and technicians should seriously reconsider the practice of clearing codes on OBD equipped vehicles when that vehicle has to return for an emissions retest.

How can readiness monitors be set?

There are many reasons the readiness monitors could be set to “not ready”. One cause is routine maintenance. For instance, if the battery is disconnected for any reason, the monitors of most vehicles are reset. Also, a service technician may have to reset them as part of the repair process. In these cases, the vehicle must be driven to reset the monitors. Some manufacturers advertise driving procedures while others do not. The vehicle manufacturer or a qualified service technician is the best source for this information. Another cause is that there is a problem with the OBD system that prevents one (1) or more monitors from running. In these cases, a qualified technician must diagnose and repair the problem before the monitor will run. Before any of these monitors set to “ready”, the components must be operated in a specific manner designed by the manufacturer that checks the performance of that particular emissions control system. However, it is important to understand that setting a monitor to “ready” does not ensure that the system is defect-free. Completed readiness monitors only indicates that the applicable component or system has been checked.

Three monitors on all OBD-equipped vehicles have been designed to continuously check for system defects. Because of this, these monitors report as complete at all times and will not cause a vehicle to be rejected during a vehicle emissions test. These continuous monitors evaluate the following emissions control systems in the vehicle:

Misfire
Fuel System
Comprehensive Components

In order to set readiness for non-continuous monitors, the vehicle must be prepared and driven in a specific manner. Monitors cannot be set using a scan tool, and the OBD system software must see the driving conditions required to run the monitor in order to complete the evaluation. These required driving conditions are referred to as “drive cycles” and define the preconditions and driving conditions necessary to set the readiness monitors.

Since many different readiness monitors may be present on a vehicle, drive cycles can be designed to set all monitors present with one (1) cycle, or an individual drive cycle can be targeted at specific monitors on the vehicle. It should be understood that both the catalyst and evaporative monitors require more driving than other monitor drive cycles.

Due to the complex interrelations between OBD system components and monitors, it is possible for one (1) defect to mask or “block” an additional defect(s). Because of this, it is possible to perform a valid repair on a vehicle only to have an additional defect identified by the readiness monitors shortly after the repair.

A special note about the catalyst monitor?

After a vehicle fails an OBD test where any of the fault codes are for catalyst efficiency, the catalyst monitor must be “ready” prior to a retest. Such vehicles presented for a retest with the catalyst monitor “not ready” will be rejected.

How does OBD help the environment?

The intent of OBD systems is to ensure proper emissions system operation for a vehicle during its lifetime by monitoring emissions-related components and systems for malfunction and/or deterioration. An important aspect of OBD is its ability to notify the driver of a problem before the vehicle's emissions have increased significantly. If the vehicle is taken to a repair shop in a timely fashion, it can be properly repaired before any significant emissions increase occurs. OBD systems also provide automobile manufacturers with valuable feedback from their customers' vehicles that can be used to improve vehicle and emissions control system designs.

How does OBD help consumers?

OBD systems are designed to alert drivers when something in the emissions control system begins to deteriorate or fail. Early diagnosis, followed by timely repair can often prevent more costly repairs on both emissions control systems and other vehicle systems that may affect vehicle performance, such as fuel economy. For example, a poorly performing spark plug can cause the engine to misfire, a condition sometimes unnoticed by the driver. This engine misfire can, in turn, quickly degrade the performance of the catalytic converter. With OBD detection of the engine misfire, the driver would be faced with a relatively inexpensive spark plug repair. However, without OBD detection, the driver could be faced with an expensive catalytic converter repair in addition to the spark plug repair.

Furthermore, manufacturers have increased incentives to build higher-quality vehicles with better performance, reduced emissions and more efficient powertrains to prevent problems that can lead to OBD detection. OBD systems also provide far more information than ever before to help auto technicians diagnose and properly repair vehicles during their first visit to the repair shop, saving time and money for consumers.

Are OBD-related repairs covered by warranty?

Federal law requires that the emissions control systems on 1995 and later model year vehicles be warranted for 2 years or 24,000 miles. Many automakers provide extended warranty coverage beyond what is currently required by federal law. Federal law also requires that the on-board computer and the catalytic converter on 1995 and later model year vehicles be warranted for 8 years or 80,000 miles.

Can anyone service an OBD-related problem?

Only qualified, trained technicians equipped with proper diagnostic and repair equipment should conduct OBD-related service. Vehicle owners should ask dealers and independent repair shops if their technicians have received proper training and have access to the necessary equipment to properly service OBD equipped vehicles. The Repair Shop Report (RSR) is an excellent resource to help select a qualified repair shop.

Vehicle Emissions Test Enforcement and Your License Plates

How does enforcement of the Vehicle Emissions Inspection Law affect me?

Will I be notified when my vehicle needs to be tested?

The Secretary of State’s Office mails License Plate Renewal Notices that include a statement as to whether compliance with the Vehicle Emissions Inspection Law is required before a vehicle’s registration can be renewed. The Secretary of State’s Office sends paperless License Plate Renewal Notices via email to individuals who register at https://www.ilsos.gov/greenmail. The electronic notices also include a statement as to whether compliance with the Vehicle Emissions Inspection Law is required before a vehicle’s registration can be renewed.

A test notice is mailed up to four (4) months prior to your vehicle’s license plate expiration reminding you to take your vehicle in for an emissions test. The Illinois EPA urges motorists to have their vehicles tested several weeks prior to your license plate expiration to allow sufficient time to complete the process. If a vehicle fails the emissions test, it may be necessary to have emissions-related repairs performed to the vehicle, and the vehicle must pass its retest prior to the time its vehicle registration expires. To determine whether your vehicle is due for an emissions test, click to be directed to our convenient Vehicle Eligibility Check tool.

Please note that while the vehicle may be tested up to four (4) months prior to license plate expiration, the plates may only be renewed within three (3) months of the expiration date.

My license plates have expired and cannot be renewed due to failure to comply with the emissions law. How do I get my vehicle tested?

If your license plates have expired, you must obtain a 7-day permit from any full-service Secretary of State driver's license facility to legally operate the vehicle while you get your vehicle tested.

My vehicle has complied. How long will it take before I can purchase a renewal sticker for my license plates?

Once a vehicle complies with the Vehicle Emissions Inspection Law, the Secretary of State's office is automatically notified electronically that the vehicle has complied; thereby allowing a renewal sticker to be sold at a Secretary of State facility, currency exchange or other authorized agent, including the high capacity drive-thru testing stations.

In rare instances, electronic communication between the testing station and the Secretary of State's system may be interrupted. Therefore it may be necessary to wait at least one (1) business day before you renew your registration.

Please note that while the vehicle may be tested up to four (4) months prior to license plate expiration, the plates may only be renewed within three (3) months of the expiration date.

Questions about Hybrid Vehicle Emissions Testing

Why does my hybrid-electric vehicle have to be tested?

While it is true that a hybrid-electric vehicle emits less emissions overall than a similar-sized gasoline-only powered vehicle when operating as designed, the potential for high emissions is still present. Hybrid-electric vehicles are equipped with the same standard emissions control devices as any other vehicle. If any of these emissions control devices deteriorates or fails during the life of the vehicle, the emissions could potentially exceed the allowable limits during gasoline operating periods. The vehicle emissions test is designed to identify these potential emissions control device problems before any significant emissions increases occur.

Are transmission codes emissions related?

If the Malfunction Indicator Light (MIL) is commanded on for a transmission code, it is emissions related. OBD II is required to monitor all power train components that effect emissions, provide diagnostic input, or receive commands from the PCM. The transmission controls the amount of power going from the engine to the wheels. If the transmission is not working properly, the efficiency of the power transfer will be degraded. Simply stated, the engine of a vehicle with a malfunctioning transmission will have to work harder to provide the same amount of vehicle speed. A harder working engine will require more fuel which will result in higher tailpipe emissions.

Does the registered owner have to be present for the emissions test?

The registered owner does not have to bring their vehicle in to be tested. Anyone can bring the vehicle in to be tested.

Do I need to get out of my vehicle during the emissions test?

Yes. All drivers are required to exit the driver’s compartment during the emissions test. This is necessary to maintain a safe working environment for both staff and patrons, as well as to prevent accidental damage to customer vehicles during the execution of the vehicle emissions test. The Air Team is committed to creating an inclusive environment and recognizes individuals with disabilities as valued members of a diverse society. The Illinois Air Team follows these guidelines to accommodate all vehicle owners during vehicle emissions tests.

Vehicle owners are not required to be present during the emissions testing of their vehicle; anyone can bring a vehicle in for its required emissions inspection.
Facilities are ADA compliant and equipped with appropriately marked accessible parking as required.
Seating for motorists is provided in all waiting areas.
Motorists requiring additional time to safely exit and re-enter the driver’s compartment will not be rushed.
It is recommended that motorists with difficulties exiting the driver’s compartment of their vehicle strongly consider having someone else bring their vehicle in for testing.