Overview of Vehicle Inspection and
Maintenance (l/M) Programs
J-
C
£
-------
Where is l/M required?
The 1990 Amendments to the Clean Air Act (CAA) mandated I/M for ozone and carbon
monoxide (CO) nonattainment areas based upon certain criteria, such as air quality status,
population, and/or geographic location. Today, I/M programs are used as an emissions control
strategy primarily in ozone nonattainment and maintenance areas - only a few are still in CO
maintenance areas.
The CAA established two performance levels of I/M programs: "Basic" and "Enhanced" I/M.
• Basic I/M programs are for ozone nonattainment areas classified as Moderate with an urbanized
population over 200,000 in 1990 and only require testing for light-duty cars.
• Enhanced I/M programs are required in areas classified as Serious, Severe, and Extreme for
ozone, and with urbanized populations over 200,000 in 1980. Also, all Metropolitan Statistical
Areas (MSA) in the Northeast Ozone Transport Region (OTR) with a 1980 population over
100,000 are Enhanced, regardless of its air quality classification. Both light-duty cars and trucks
must be inspected in Enhanced I/M areas.
The map below highlights counties across the country with I/M programs:
I/M Programs by County
WA
OR
MT ND I ' ME
mn >t2b r 7*.'
ID
WY
SD W
IA
Ml
I'1'-)/-' "> y-L
-------
Overview of l/M Testing
In general, there are three types of I/M testing: visual inspections, tailpipe testing and on-board
diagnostic (OBD) checks. I/M programs may use all or a combination of these.
• Visual inspections deter tampering by checking for the presence of certain required emission
control parts (e.g., catalytic converter replaced with a straight pipe).
• Tailpipe testing consists of measuring the exhaust emissions at idle or under certain engine
loads primarily for vehicles that are model year 1995 and older.
• Beginning with the 1996 model year, vehicles have been equipped with
OBD computerized systems. The OBD system continuously monitors the
emission control systems and will activate the "Check Engine" light on the
dashboard if a fault, also known as a Diagnostic Trouble Code (DTC), is
detected - most commonly from the catalytic converter or an oxygen sensor.
_vl / /
**
[ SOON!
In general, vehicles that fail inspection must be repaired and be retested. Additionally, if a vehicle
owner or operator modifies their vehicles' emission control systems, any 'tampering' identified
during the inspection is required to be restored to the intended configuration.
States are responsible for developing their own I/M program to meet EPA's I/M regulations
(40 CFR part 51, subpart S), and vehicle testing requirements vary across the country. For example,
some states do not require testing for newer vehicles because these vehicles likely still have emission
control systems that are functioning properly or are covered under warranty. Additionally, certain
vehicles may be exempt, like classic automobiles, motor homes, agricultural vehicles, and hybrid
vehicles. Also, some states offer repair or hardship waivers based on the cost of repairs made as the
result of a failing inspection.
Benefits of I/M Testing
In 2018, nearly 68 million vehicles were inspected nationally, and 3.5 million vehicles, or 5%, initially
failed. However, more than 75% of those vehicles that failed were repaired to meet the federal emission
standards and are operating with reduced emissions. In addition, OBD I/M programs can yield
emission benefits even from vehicles that do not fail a test. For instance, many motorists, when seeing
the OBD "Check Engine" light is on, will elect to repair their vehicle prior to their required inspection.
More Information
For more information about I/M in your area, please visit your state's I/M site:
www.epa.gov/state-and-local-transportation/vehicle-emissions-inspection-
and-maintenance-im-tampering-warranty
For questions concerning a particular state or program area, please contact the Mobile Source
Contact at your EPA Regional Office (Section 16):
www.epa.gov/transportation-air-pollution-and-climate-change/ office-transportation-
and-air-quality-contacts-topic
For general information in I/M, please visit the U.S. EPA site:
www.epa.gov/state-and-local-transportation/vehicle-emissions-inspection-and-maintenance
3
------- |