FAQs: ASM/TSI Emissions Testing

ASM/TSI Testing

Understanding Tailpipe Failures


ASM Emissions Test
What is ASM2 and how does it work?
This test uses a dynamometer, which measures emissions under simulated driving conditions. In a sense, it's like a treadmill stress test for your vehicle. This tailpipe test is a cost-effective way to get very accurate, realistic results. A vehicle will fail the test if there is an excessive amount of Hydrocarbon, Carbon Monoxide or Oxides of Nitrogen.

Please note that 4 wheel drive vehicles will continue to receive the current Two-Speed Idle test. If your vehicle fails the ASM test, you can return to the same public inspection station within 15 days of your initial test for a free retest.


Two Speed Idle Test
The Two-Speed Idle test is a tailpipe emissions test. This means the analyzer measures exhaust emissions directly from the vehicle's tailpipe with the engine idling at a high and then low speed. TSI measures most of the common factors contributing to the formation of lung damaging ground level ozone.

A vehicle will fail the test if there are excessive amounts of hydrocarbons or carbon monoxide. TSI is used for older vehicles that are not equipped with the advanced on-board diagnostic computer system.


A Few Reasons Why A Vehicle May Fail the ASM2 Test

Excessive Hydrocarbons (HC):
High hydrocarbon emissions result when fuel in the engine does not burn completely. HC in the presence of oxides of nitrogen (NOx) and sunlight may form ground-level ozone, a major component of urban smog. Check the following:

Excessive Carbon Monoxide (CO):
A rich fuel mixture can cause high amounts of carbon monoxide, which can occur when there is too much or too little air reaching the combustion chamber. Check the following:

Excessive Oxides of Nitrogen (NOx):
High NOx can occur when there is excessive temperature in the combustion chamber or a damaged catalytic converter.
Check the following:


Diagnostics for NOx failures

OVERALL
Check for causes of high combustion temperatures. Primary systems that affect NOx include:

1981-86
Check the following:

1987-95
Check the following:


Diagnostics for HC failures

OVERALL

1981-86
Check the following:

1987-95
Check the following:


Diagnostics for CO failures

OVERALL
Check for cause of rich mixture, e.g. Oxygen Sensor

1981-86
Check the following:

1987-95
Check the following: