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
1996 282,014 53,131 32,714 12,696 4,170
1997 362,253 58,975 37,674 14,092 4,803
1998 417,595 63,516 38,419 15,177 4,897
1999 504,492 69,563 41,368 16,624 5,273
2000 629,684 79,718 45,337 3,573 1,084
2001 685,541 98,512 47,302 4,415 1,131
2002 691,076 77,953 40,773 3,494 975
2003 718,757 62,101 35,219 2,783 842
2004 721,636 49,649 12,266 2,225 293
2005 709,406 29,511 8,513 1,323 204
2006 725,813 23,081 6,532 1,034 156
2007 736,341 11,266 3,682 505 88
2008 752,711 9,936 4,516 445 108
2009 786,510 4,562 4,719 136 75
Total 8,723,825 691,480 359,037 78,523 24,100

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.