Testing Q&A

How often must I have my vehicle tested?

Testing is required every other year. Motorists are notified of their testing month by mail. (The testing year interval starts from when the vehicle was last due to test, not when it is tested.) Vehicles will be tested every two years based on the model year of the vehicle and corresponding calendar year. For example, if your car was manufactured in an even year, it will be tested in even year.

I am new to Ada County. What do I need to do to fulfill the emissions testing requirements?

Idaho state law requires model year 1981 and newer gasoline and diesel-powered vehicles older than four years to be tested every other year. State law requires that you register your vehicle in the county in which you have your principal residence or domicile and update that registration record whenever that residence changes. After your vehicle has been registered with the Department of Motor Vehicles your vehicle will be assigned a testing due date, you will receive a testing notice mailed to the address on the vehicle’s registration prior to your testing due date. Unless the vehicle is being tested for informational purposes, motorist should wait for an emissions testing notice to be received before testing.

How much does testing cost?

The maximum cost of an emission test is $20; the fee is due at the time of testing. If the vehicle fails the test, a fee up to $16.50 (defined by the station owners) will be required at the time of testing. A motorist is allowed one free re-test, if completed within 30 days of the original test and at the same station. If a late notice was processed, an additional processing fee of $5 will be added.

What vehicles need to be tested?

Model year 1981 and newer gasoline and diesel-powered vehicles older than four years must be tested.

What vehicles do not need to be tested?

• Electric or hybrid motor vehicles

• Motor vehicles with a model year less than four years old

• Motor vehicles with a model year older than 1981

• Classic automobiles as defined by Idaho Code

• Motor vehicles with a maximum vehicle gross weight of less than 1,500 pounds

• Motor vehicles registered as motor homes as defined by Idaho Code

• Motorized farm tractors

What happens if I don’t have my vehicle tested?

Your vehicle registration will be revoked by Idaho Transportation Department (ITD). If that occurs, before you can legally drive the vehicle again, you would need to comply with a passing test. Registrations will be reinstated at no charge after passing emissions test.

How are emissions tested?

Gasoline-powered vehicles are tested by one of two methods, depending on the age of the vehicle:

Type 1: The Two-Speed Idle (TSI) method used on model year 1981-1995 gas-powered vehicles, samples a vehicle’s exhaust to see if it is above or below standards.

Type 2: The On-Board Diagnostic (OBD) system, used on model year vehicles 1996 and newer, looks for broken or malfunctioning emissions control components.

Diesel-powered vehicles are inspected by a snap acceleration test that uses a smoke meter at the end of the exhaust pipe or the OBD system depending on the vehicle model year.

Additional Testing

Gas caps are inspected for leaks. On model year 1995 and older gas-powered vehicles, gas caps are removed and tested to ensure they seal properly. On model year 1996 and newer vehicles, the OBD system automatically performs the test.

All vehicles are subject to a visual inspections of emissions control equipment.

How is a TSI test conducted?

1. The inspector visually checks the vehicle for required emissions control devices and performs a pressurized gas cap test.

2. The inspector places a probe in the tailpipe that measures hydrocarbons and carbon monoxide. A tachometer lead is attached as applicable to monitor proper revolutions per minute (rpm) at test intervals.

3. The analyzer samples the emissions at two different stages a high idle and a low idle if at any time within the two stages of testing the vehicle meets the criteria the test is complete and the overall test result is a pass.

If the vehicle’s sample fails stage one it is tested at stage two, if it fails both stages the overall test result is a fail. At the conclusion of the test the analyzer tells the inspector the results of the emissions test.

What can cause my vehicle to fail a TSI test?

Several common conditions can cause a vehicle to fail an emissions test. Such as: levels of hydrocarbons are too high in the vehicle’s tailpipe emissions; levels of carbon monoxide are too high in the vehicle’s tailpipe emissions; an emissions control device is missing or not functioning properly; the vehicle’s exhaust has too many holes, preventing a constant, testable flow; the vehicle is not safe for testing.

My car didn’t pass the TSI test. What should I do?

In most cases, the vehicle needs to be repaired. If you take the vehicle to a repair shop, bring the vehicle inspection report (VIR) you received from the testing station. Various mechanical issues can lead to emissions problems: excessive amounts of hydrocarbons and/or carbon monoxide can be caused by problems with the ignition system, the air/fuel mixture, or other engine issues; missing or defective emissions control devices will need to be repaired or replaced; blue smoke can indicate that engine oil is being burned in the combustion chamber. Black smoke can indicate that the fuel mixture is overly rich.

I think my vehicle will fail, so what good will a test do?

TSI tests can provide clues about what’s wrong with a vehicle. Early repairs of minor problems can prevent more significant problems from developing. A failed emissions test is necessary to qualify for a waive

How does the "Check Engine Light" relate to OBD-II?

The Check Engine light will illuminate when the same emissions Diagnostic Trouble Code has been detected more than once. This light alerts the driver that the vehicle needs to be repaired. Federal regulations require that the check engine light only be illuminated for emissions-related malfunctions.

How is an OBD-II test conducted?

Idaho’s OBD-II inspection involves three steps:

1. The inspector visually checks the vehicle for required emissions control devices.

2. The inspector verifies the “Check Engine” light bulb is working and does not stay on when the engine is started.

3. The inspector plugs the analyzer into the vehicle’s OBD-II diagnostic link connector to access the on-board computer, which then reports the status of the OBD-II system.

Why do you use the OBD-II instead of testing emissions from the tailpipe?

An OBD-II emissions test is faster and more thorough than a tailpipe emissions test. It is also widely accepted, nationwide, as the standard for testing emissions of 1996 and newer vehicles. Idaho uses the OBD-II system to verify emissions compliance. The simple "plug-in" test asks the vehicle’s OBD-II system if it has it found any problems. If the check engine light is not illuminated and the OBD II system does not detect diagnostic trouble codes, the vehicle is assumed to be in emissions compliance and passes the test.

I have a 1996 or newer vehicle and my check engine light is on, but the emissions from my tailpipe are below the standard. How can I fail the emissions test?

Vehicles that were manufactured in 1996 or later (and were manufactured more than four years ago) are required to have an on-board diagnostic (OBD-II) emissions test. The federal government has mandated that 1996 and newer vehicles be equipped with an OBD-II system. The OBD-II system monitors the performance of emissions control devices while the vehicle is being driven. If the check engine light is illuminated, the OBD II system has detected a diagnostic trouble code(s). The vehicle is not operating as designed and this will result in a failed emissions test.

Why can’t I have a tailpipe test instead of an OBD-II test?

An OBD-II test is more thorough than the two-speed idle (tailpipe) test and can check both emissions from a tailpipe and evaporative emissions. It is also less time-consuming. If possible, an OBD-II test would be a component of all emissions tests. However, older vehicles are not equipped with the technology that makes OBD-II testing possible.

I failed my emissions test due to a Diagnostic Trouble Code (DTC) specific to the transmission. How does the transmission affect emissions?

The efficiency of the transmission directly correlates to how hard the engine is running. If the engine is working harder than it normally would, there is an increase in emissions because the vehicle is not operating as efficiently as designed.

Are OBD-II repairs covered by my warranty?

Federal law requires emissions control systems on vehicles be warranted for two (2) years or 24,000 miles. Many auto manufacturers provide extended warranty coverage. Federal law also stipulates that catalytic converters be covered for eight (8) years or 80,000 miles. Consult the owner’s/warranty manual to find out about your vehicle’s coverage.

My check engine light is on so I know my vehicle will fail an emissions test. What good will it do to have the test?

OBD-II tests often reveal DTCs that can help an individual to determine what is wrong with a vehicle. A failed emissions test is necessary to qualify for a waiver

My car didn’t pass the OBD-II test. What should I do?

If the check engine light will not illuminate when the engine is off and the key is on, the bulb and/or circuitry must be repaired. If the check engine light stays illuminated when the engine is turned on, the OBD-II system has found an emissions control problem that needs to be repaired. If readiness monitors are not set, it may be because the battery has been disconnected or replaced, or the car has had recent maintenance in which the DTCs have been cleared with an OBD scan tool. In most cases, driving normally for an additional one to two weeks (up to 1,000 miles) will reset the readiness monitors. Consult your vehicle owner’s manual for specific drive cycle information.

Do Diesel vehicles require testing?

Yes - Model year 1981 and newer gasoline- and diesel-powered vehicles older than four years with a GVWR less than 14,001 must be tested. Diesel-powered vehicles are inspected by a snap acceleration test that uses a smoke meter at the end of the exhaust pipe or the OBD system depending on the vehicle model year.

What repairs are common after a failed emissions test?

The following are the most common emissions control devices that often need to be repaired or replaced.

1. Catalytic converter—reduces the amount of pollutants in the exhaust stream by converting them to a safer form.

2. Oxygen sensor—measures the proportion of oxygen in the exhaust stream. The electronic control module then uses this information to ensure that the fuel/air ratio is ideal for combustion.

3. Hoses and gaskets—prevent vacuum leaks when properly maintained. Vacuum leaks cause the gasoline/air mixture to run lean (too much air, not enough fuel), which causes incomplete burning of gasoline. Vacuum leaks often decrease fuel efficiency.

Consult a certified mechanic for additional information.

Why must my vehicle test back to back, when it has already passed one emissions test this cycle?

Vehicles that are greater than two years past due on emission testing will be required to complete two consecutive emission tests in order to get a vehicle reinstated. A message will be provided on the first passing test stating an additional test will be required.

A message will be displayed on the first passing test stating an additional test will be required: This test brings you into compliance with your prior testing requirement, however an additional test is still required for reinstatement of your vehicle.

Am I required to have my vehicle’s emissions tested?

If your vehicle is registered in Ada County, state law requires that you have it tested under the provisions of the Idaho Vehicle Inspection Program. Model year 1981 and newer gasoline and diesel-powered vehicles older than four years must be tested. State law also requires that you register your vehicle in the county in which you have your principal residence or domicile. A principal residence or domicile cannot be a person's workplace, vacation, or part-time residence.

I tested my vehicle last year, why am I getting a notice to test again now, aren’t the tests good for two-years?

Notices are sent based on when the vehicle was last required to have been tested, not when the vehicle was actually tested.