Welcome to the Connecticut Emissions Program

OBD stands for On-Board Diagnostics. Most 1996 and newer vehicles have standardized computer systems (also known as OBDII) that continually monitor the electronic sensors of engines and emission control systems, including the catalytic converter, while the vehicle is being driven to ensure they are working as designed. When a potential problem is detected, a dashboard warning light called a malfunction indicator light (MIL) is illuminated to alert the driver.

An OBD system detects a problem well before symptoms such as poor performance, high emissions or poor fuel economy are recognized by the driver. An OBD emission test provides a more comprehensive picture of a vehicle’s emissions status because it evaluates emissions during everyday operating conditions whereas a tailpipe test measures emissions only at a particular moment in time. Early detection helps to avoid costly repairs and improves vehicle emissions.

For more information on OBD emission testing log on to the United States Environmental Protection Agency at www.epa.gov/obd/

What are the usual reasons for an OBD Failure?

A vehicle will fail an OBD emissions test for the following reasons:

– MIL light remains ON while vehicle is running
– OBD Monitor(s) are Not Ready
– OBD Connector is missing, damaged or inaccessible
– OBD Communication failure

What is a ‘Malfunction Indicator Light” (MIL)?

The Malfunction Indicator Light is commonly referred to as the check engine or service engine light. Following are the usual symbols that most manufacturers use to represent the MIL:


What is the purpose of the ‘Malfunction Indicator Lamp’ (MIL)?

During everyday operation, the MIL light will illuminate for a few seconds when a vehicle is first started and extinguish when the engine is running. When the MIL light remains on during normal vehicle operation, the OBD system has detected a problem(s) with the vehicle’s engine, transmission or emission control system. Do not ignore this warning!

NOTE: If the MIL light is continuously ON when the vehicle undergoes an emission test, the result will be a FAIL.

What Does It  Mean When My Vehicle’s MIL remains on?

The OBD system has indicated that it detected that your vehicle has an emission problem by illuminating the MIL light and has stored a Diagnostic Trouble Code (DTC) in the vehicle’s computer memory.

Sometimes, the OBD system will automatically turn off the MIL light if the conditions that caused the problem are no longer present. This will happen when the OBD system evaluates a component or system three consecutive times and no longer detects the initial problem.

For example, if a gas cap is not properly tightened after refueling, the OBD system may detect vapor leakage and turn on the MIL light. If the gas cap is tightened, the OBD system will recognize this and the MIL light will be turned off after a few days of driving.

What Should be Done When the MIL remains ON?

The OBD system is alerting you that the vehicle should be looked at soon by a Certified Emission Repair Technician. Timely diagnosis may save you money in two ways:

Small problems are identified before they become major expenses

A faulty component may be covered by the vehicle’s emission warrant

What does it mean when my vehicle’s MIL is flashing?

A flashing MIL light indicates that your vehicle’s engine is seriously misfiring. Because this condition may cause the catalytic converter to overheat and cause a fire, you should stop driving the vehicle and have it attended to by a Certified Emission Repair Technician as soon as possible.

If this problem is not addressed quickly, the resulting repairs may be very expensive.

My vehicle failed its OBD emission test for Readiness?

When a vehicle fails an OBD emission test due to excessive OBD monitors not ready it indicates that your vehicle’s OBD system was Not Ready to perform its examination of the emission control system because the required number of monitors had not completed their analysis of the vehicle’s emission control system.

What does ‘Not Ready’ mean?

The OBD system continually collects data on your vehicle’s everyday operation to determine if it would pass an OBD emission test. In most cases, Not Ready is a result of a battery being disconnected or a scan tool turning the MIL light off during repair work causing the monitors to be unset.

NOTE: Disconnecting the battery, a dead battery or low voltage battery or clearing the OBD computer prior to an emission test will result in an emission test failure for Readiness.

If My Vehicle Failed for ‘Readiness’, What should I do next?

Normally, a week of combined highway and city driving, known as drive cycles, will reset the OBD monitors thereby allowing an OBD test to be completed. Following are some suggestions that should allow the OBD system to become Ready:

– Drive the vehicle at least three separate times in which it is turned on and off
– One drive cycle should be local in-town driving
– One drive cycle should be highway driving
– One drive cycle should be after the vehicle was unused for a period (overnight etc.)
– The gas tank should be ¼ to ¾ full.
– Drive the vehicle smoothly and avoid rapid acceleration

NOTE: If the vehicle failed for Unset Readiness, upon retest the required number of monitors must be ready or the emission test will be aborted.

NOTE: If the vehicle initially failed for a catalyst related DTC, the catalyst monitor must be READY to complete a retest.

NOTE: If you still encounter difficulty getting your vehicle’s monitors Ready after performing these drive cycles, some new car manufacturers may be able to set the monitors to Ready with their diagnostic computer.

If you are unable to get your vehicle ready for an OBD emission test, you may have a Certified Emission Repair Technician perform a drive cycle conditioning. Please ask if there is any cost for this service.

What Is a Certified Emission Repair Technician?

A Certified Emission Repair Technician (CERT) is an automotive technician who has successfully passed a State of Connecticut required training program devoted specifically to the repair of emission problems.

A repair facility that employs a Certified Emission Repair Technician is designated as a Certified Emission Repair Facility (CERF).

Where can I find a Connecticut Certified Repair Facility?

Along with the Vehicle Inspection Report indicating that your vehicle failed, you will receive a listing of Certified Emission Repair Facilities (CERF) nearby to the Test Station.  A listing for another area may also be requested.