Emission Test Definitions
Visual Check
What is a Visual Anti-Tampering Check?
The Visual Anti-Tampering Check is a visual inspection for
the presence of emission control components that were installed
on your vehicle by the manufacturer.
How is a Visual Anti-Tampering Check performed?
A certified technician will look for the presence of the
following emission control devices:
- Catalytic converter
- Exhaust gas recirculation (EGR) valve
- Positive crankcase ventilation (PCV) valve
- Fuel inlet restrictor
- Air pump
- Evaporative control system components such as vapor
canisters and lines.
The certified technician will also determine if these
devices are properly connected and if they are the correct
type for the vehicle being inspected.
Gas Cap Test
What is a Gas Cap Test?
A Gas Cap Test is a functional check that tests whether
harmful evaporative emissions (fumes) are escaping from
a vehicle's gas tank into the atmosphere.
How is a Gas Cap Test performed?
A certified technician will remove the gas cap and insert
it into a device that will then apply pressure to the gas
cap. The testing unit will verify that the gas cap holds
pressure for the period of approximately 45 seconds and
a determination will be made as to whether or not fumes
are escaping.
Single Speed and Two Speed Idle Tests
What is a Tailpipe Test?
A Tailpipe Test uses a tailpipe probe to collect a sample
of the exhaust and an emissions analyzer to measure pollutants.
The Tailpipe Test can be performed on many gasoline-powered
passenger vehicles, vans and light-duty trucks. Inspection
requirements are based on each vehicle's model year, with
an allowance for normal wear.
How is a Tailpipe Test performed?
First, a certified technician will verify that the vehicle's
engine is running at operating temperature. Then, the technician
will insert a probe into the tailpipe to capture a sample
of the engine's exhaust. After approximately 30-45 seconds,
the analyzer will determine whether or not the vehicle is
emitting excess pollutants based on the vehicle's model
year.
What is an idle test?
A Tailpipe Test is performed while the engine is idling.
A one-speed idle test uses engine speeds between 450 rpm
and 1100 rpm, while a two-speed idle test checks emissions
at two different engine speeds, the regular idle and a fast
idle around 2500 rpm.
Dynamometer
What is a Tailpipe Test?
A Tailpipe Test uses a tailpipe probe to collect a sample
of the exhaust and an emissions analyzer to measure pollutants.
The Tailpipe Test can be performed on many gasoline-powered
passenger vehicles, vans and light-duty trucks. Inspection
requirements are based on each vehicle's model year, with
an allowance for normal wear.
How is a Tailpipe Test performed?
First, a certified technician will verify that the vehicle's
engine is running at operating temperature. Then, the technician
will insert a probe into the tailpipe to capture a sample
of the engine's exhaust. After approximately 30-45 seconds,
the analyzer will determine whether or not the vehicle is
emitting excess pollutants based on the vehicle's model
year.
What is a Tailpipe Test using a dynamometer?
A Tailpipe Test using a dynamometer uses an emissions analyzer
and a treadmill-like device, called a dynamometer, which
puts a load on the engine to simulate driving conditions
at 15 miles per hour. The Tailpipe Test using a dynamometer
can be performed on many gasoline-powered passenger vehicles,
vans and light-duty trucks. Inspection requirements are
based on each vehicle's model year, with an allowance for
normal wear. The dynamometer test used in the Philadelphia
area is called ASM for Accelerated Simulation Mode.
How is a Tailpipe Test using a dynamometer performed?
First, a certified technician will verify that the vehicle's
engine is running at operating temperature. Then, the technician
will place the vehicle's drive wheels on the dynamometer
rollers. The technician will then insert a probe into the
tailpipe to capture a sample of the engine's exhaust. After
approximately 30-45 seconds, the analyzer will determine
whether or not the vehicle is emitting excess pollutants
based on the vehicle's model year.
Why is a dynamometer used for some Tailpipe Tests?
In the Philadelphia region, where air pollution is more
severe, it is necessary to reduce harmful oxides of nitrogen
(NOx). To do this, the vehicle's engine must be tested while
under load. The treadmill-like device is the only method
of applying a load to the vehicles drive wheels to test
for NOx.
Onboard Diagnostics (OBD) Check
What is On-Board Diagnostics (OBD)?
OBD is an on-board system comprised of a computer with diagnostic
software and sensors. The OBD system monitors the performance
of the ignition, fuel metering and emissions systems, including
the sensors and the computer itself, while the vehicle is
being driven to insure they are working "as designed." The
on-board computer has the ability to identify a problem
well before the driver may recognize symptoms. The computer
will illuminate a light on the dash to notify the driver
of a problem. Most dash lights will display a "Check Engine,"
"Service Engine Soon," or an engine symbol. When the OBD
system detects a problem, a diagnostic trouble code is stored
in the vehicle's computer. When a vehicle is brought in
for an official OBD I/M Check, those trouble codes will
help a technician properly diagnose and, if necessary, repair
the problem. The OBD I/M Check can be performed on most
1996 and newer model-year gasoline-powered passenger vehicles,
vans and light-duty trucks weighing 8,500 pounds and less,
since these vehicles were required by the EPA to be manufactured
with OBD systems.
How is an OBD I/M Check performed?
A certified technician will attach a cable to the vehicle's
on-board computer through a data link connector (DLC), usually
found under the dashboard, and download information to a
computer to access how well the vehicle's emissions system
is functioning. The vehicle's on-board computer will generate
diagnostic trouble codes (DTC's) if there are malfunctions
or other problems present in the vehicle's emissions system.
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