Vehicle Inspection & Maintenance Program: OBD II Test Validity & Reliablity

Abstract:

The vehicle inspection and maintenance (I/M) program is one of the mitigation measures, which provides ‘co-benefits’ in the reduction of both air pollution and greenhouse gas emissions. Many countries in Asia already have the I/M program in place for some times. Environmental agencies might consider the adoption of on-board diagnostic II (OBD II) test to replace the tradition tailpipe emission test because OBD II is easy to use, inexpensive in terms of technology, and faster for each testing transaction. Despite all advantages, OBD II test is not far from error. As shown in this paper, from the US experience, switching testing method from tailpipe emission to OBD II can lead to less effective emission reduction. Specifically, OBD II test can pass old vehicles which are the most likely high emitters. Evidently, the I/M program in Asian countries can benefit from this US study by taking the limitations of the OBD II system into account when planning to change to OBD II testing method. In 2002, the Atlanta I/M program replaced the tailpipe emission test with the new testing method using the OBD II computer installed in every vehicles of model year 1996 onward. Instead of tailpipe emission, the pass/fail result of the new test method only depends on the trouble codes stored in the OBD II. As vehicles become older and likely to pollute more, OBD II system is prone to malfunction as well. This study aims at evaluating the effectiveness of the Atlanta I/M program by testing the validity and reliability of OBD II test over time. By comparing the OBD II test results with the real tailpipe emission measurement from on-road vehicles obtained by remote sensing device (RSD), the study can determine the difference of validity and reliability between old and new groups of vehicles.

Keywords: Atlanta, vehicle inspection and maintenance program, OBD II test, validity and reliability