1982 and Newer Model Year Vehicles
1982 and newer gasoline-powered passenger cars and light duty trucks must be tested every other year as a condition of obtaining a vehicle registration. These vehicles are tested with either the On-Board Diagnostics (OBD) "plug-in" test or the I/M 240 test that can be likened to a "treadmill" test for your vehicle.
New vehicles do not require an emissions test until the eighth model year. For example, a 2010 model year vehicle is not due for an emissions inspections until 2017.
Pursuant to House Bill 1214, a vehicle being registered in the program area for the first time may be registered without an inspection or certification if the vehicle has not yet reached its seventh model year.
OBD Emissions Test
The vehicles on-board computer port is connected, via an OBD cable, to the inspection station computer. The inspector starts the engine to verify that that the "Check Engine" light turns on. The inspector then starts the engine to verify that the "Check Engine" light does not stay on while the engine is running. The OBD equipment communicates with the vehicle, checks its "Readiness" monitors - monitors that continuously check the vehicle while it is operating to detect emissions-related problems - to ensure that the system is functional, and verifies that that the computer has turned the "Check Engine" light on or off.
I/M 240 Emissions Test
The I/M 240 tests for carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NOx) during a simulated driving cycle on a treadmill-like device called a dynamometer; typical driving activities such as idling, cruising, acceleration and deceleration are performed while pollution is collected from the tailpipe.
The name of the I/M 240 test means "Inspection and Maintenance," with 240 representing the length of the treadmill test in seconds (240 seconds, or four minutes). Pollutants are measured in grams per mile (gpm), and emissions limits are set by vehicle type and model year.
Two-speed Idle Emissions Test
1981 and older model year vehicles are tested annually with the Two-Speed Idle Test.
An inspector guides the vehicle into the inspection lane and performs a brief safety check, enters the vehicle identification number (VIN) into the computer. Here all vehicles receive dashboard warning light and gas cap pressure checks. Customers are directed to enclosed waiting areas from which they can observe the inspection. Finally, vehicles move on to one of three different types of tests determined by the age of the vehicle.
OBD (On-Board Diagnostics) - non-driving "plug-in" test
The vehicle is moved into position and turned off. The inspector then plugs an OBD cable into the vehicles on-board computer port. The inspector turns the vehicle key to the on position to illuminate the dashboard lights and verify that the Malfunction Indicator Light (MIL) or "Check Engine" light turns on. The inspector then starts the engine to make sure that the "Check Engine" light does not stay on while the engine is running. The OBD equipment communicates with the vehicle, checks its readiness monitors to ensure that the system is functional, and verifies that the computer has turned the "Check Engine" light on or off. The engine is shut off and the OBD connector is unplugged. The vehicle is moved forward, the customer is given a report detailing the test results, and the inspection fee is collected.
The vehicle will require an alternate I/M 240 test if...
...the vehicle's OBD system cannot connect or communicate with the inspection station's computer,
...the vehicle's "readiness" monitors are not set.
I/M 240 dynamometer - "treadmill-like" driving test
In addition to the required initial checks of the dashboard warning lights and gas cap, a visual inspection of all required emissions equipment is conducted on most 1995-and-older model year vehicles. Once these are completed, the vehicle is moved forward and positioned on the The vehicle is positioned with its drive wheels on the dynamometer, allowing it to be tested under actual driving conditions. A fan is positioned in front of the vehicle to simulate wind and keep the engine cool throughout the test. During the driving simulation, emissions are collected from the tailpipe and analyzed. On the basis of emissions data, some very clean vehicles receive a "fast pass" while others have to be tested for the full four-minute cycle.
An automatic "second chance" test is provided for vehicles that fail by a small margin. If the vehicle fails within 200% of a pollution limit, the computer will instruct the inspector to run a second test. This is done to minimize the chance that a vehicle might fail simply because of an anomalous situation. For example, the vehicle may fail because it was not sufficiently warmed up.
The vehicle is moved off the dynamometer, and the customer is given a Vehicle Inspection Report detailing the test results and the inspection fee is collected.
The vehicle will require an alternate OBD test if...
...the vehicle is unable to be tested on the dynamometer for various reasons, such as tire or wheel base size.
Two-Speed Idle - non-driving, tailpipe test
In addition to the required initial checks of the dashboard warning lights and gas cap, a visual inspection of all required emissions equipment is conducted on vehicles model years 1975 through 1981. Once these are completed, the vehicle is moved forward and a cone is connected to the tailpipe to capture emissions. An RPM (engine speed) monitor is attached to the vehicle in a location that will best read the engine's speed. The engine will be operated at idle for about 30 seconds and then accelerated gradually (while still idling) until it reaches 2,500 RPM. The engine is held at 2,500 RPM for another 30 seconds and then gradually slowed back to idle for a final 30 seconds. The vehicle is moved forward, and the customer is given a report detailing the test results, and the inspection fee is collected.
All-Wheel Drive/Traction Control Vehicles
Vehicles that are full-time four wheel drive, all-wheel drive or are equipped with non disengagable traction control are tested using specially-designed dynamometers -- one set for the front wheels and an adjustable set (adjusted based on length of wheel base) under the rear wheels. All but one inspection station have at least two all wheel drive dynamometers and the aforementioned vehicles are tested in this lane. Vehicles that can be shifted from four-wheel drive to two-wheel drive must be tested in two-wheel drive.
Possible reasons a vehicle could be rejected from testing:
- One or more dashboard warning lights illuminated, such as brake light warning, oil light warning, or low coolant warning.
- Defective tires, such as cord showing, uneven wear or temporary spare tire.
- Driver's side door unable to open.
- Inadequate braking power.
- Vehicle unstable on dynomometer/possible alignment problem.
- Vehicle overheating.
- Fluid leak of any kind.
- Clutch or transmission slipping.
This is not an all inclusive list.
The following Colorado motor vehicles are exempt from emissions testing:
- Newly-manufactured vehicles, for the first seven (7) model years, or until a change of ownership in the last year of its exemption
- Pre-1975 collector-plated vehicles
- Pre-1942 horseless carriage-plated vehicles
- Vehicles with a two-stroke engine manufactured prior to 1980
- Vehicle registered as "kit" cars
- Farm-plated vehicles
- Solely electric powered vehicles