As vehicles have progressed through this age of computerization so has Emission Testing. Starting in the early 1970's many states adopted some type of emission testing. This process gave them a continuous means of controlling pollutants coming from the growing fleet of motor vehicles driving on their roads year after year.
The most common test in those early days was an idle test, which using a 2 or 4 Gas Analyzer, checked for excessive Carbon Monoxide (CO) and Hydrocarbons (HC). This test was widely used for almost two decades when, as the result of the amendments to the Clean Air Act in 1990, some states were forced to adopt enhanced testing. This more intense testing procedure included a check of Oxides of Nitrogen (NOx) levels and required the vehicle to be driven on a Dyno. This Dyno test was designed to mimic the Federal Test Procedure (FTP) with the hope of giving much more accurate data. For many states however this presented a logistical nightmare. Long lines at state run inspection facilities were already a problem for the consumer and many state legislators did not want to make a bad problem worse. In some cases the answer was to privatize the process while in others a modified IM240 was a better answer. Consequently many states use an Acceleration Simulation Mode (ASM) test. They go by names like ASM 5015 or ASM 2525. There are also different variations of the FTP test including IM240 (4 minute drive cycle simulating Urban and Highway driving). Some other tests are IM93 and IM293.
In the last 10 years there has been yet another shift in testing to OBD only. Many states have incorporated the OBD test with tail pipe testing in an effort to gather data. This data has been used to make a case for OBD only testing and has swayed many state environmental agencies to give it the thumbs up. California will implement OBD testing on 2000 and newer passenger cars and light duty trucks this year. They join a long list of states that are making this transition.
Many in the industry argue that OBD will not fail as many polluters as tail pipe testing but the data paints a completely different picture. The table below gives a clear indication that as On Board Diagnostics grew in its accuracy and sophistication the percentages of vehicles missed by OBD is almost insignificant.
Table C-2: Estimated Number of ASM Failing Vehicles "Missed" by OBDII Inspection Program - CY 2015
|Model Year||Initial Tests Based on Vehicle Pop||Total # ASM Failures||Total # ASM GP Failures||# ASM Failures Missed||# ASM GP Failures Missed|
Mobil Source Control Division – California Air Resources Board
Although 5 Gas Analysis still remains a very important diagnostic tool, it seems as far as the regulatory side of our business is concerned, the analyzer and dynamometer may have lived out their usefulness.