Vehicle inspection and maintenance (I/M) programs help improve air quality by identifying cars and trucks with high emissions and that may need repairs.Checked 2026-08-12
Emissions inspection
A state or local test of a vehicle's emissions performance, often required to register it.
Also called: smog check · emissions test · I/M test
What it means
Definition
Emissions inspections are run as state or local Inspection and Maintenance programs, which the EPA describes as helping improve air quality by identifying cars and trucks with high emissions and that may need repairs. On most vehicles the test reads the OBD-II system rather than sampling the tailpipe. Coverage is not national: the EPA notes that I/M programs vary from area to area, and some states and counties run none at all.
Why a buyer cares
What it changes
Where a program exists, registration can depend on passing it, and a car whose monitors are not ready cannot complete an OBD-based test until it has been driven enough for them to finish.
In practice
Where you meet it
At an authorised testing station at registration or renewal, and on the inspection report itself.
Two things that look alike
Not the same as
A safety inspection covers brakes, lights and structure. Some states combine the two into one visit, but they test different things.
Read next
Related terms
OBD-II (On-Board Diagnostics II)
The standardised self-diagnostic system in modern cars, read through a connector under the dash.
Readiness monitors
Self-tests the OBD-II system must complete before an emissions test can be read.
Malfunction Indicator Lamp (MIL)
The dashboard lamp — usually labelled Check Engine — that the OBD-II system switches on when it confirms a fault.
Where this comes from
Sources
Because I/M programs vary from area to area, please visit the applicable link below for more information on your area's I/M programChecked 2026-08-12