Abstract
Keywords -
OBDII comparison tailpipe emissions testing
Abstract -
During 2002, the implementation of vehicle On Board Diagnostics II (OBDII) as a means to determine emissions inspection failures for in-use vehicles occurred in some government mandated Inspection/Maintenance (I/M) programs within the United States of America (U.S.A.). In prior years, progress toward implementing OBDII-based I/M inspections involved controversy regarding the suitability of OBDII as a substitute for actual emissions tailpipe measurements. Much of this controversy resulted from early research conducted in laboratory environments on a limited number of vehicles and sponsored by government agencies. Now that actual OBDII-based inspection programs have been in place for more than a year, we are able to analyze real-world, statistically significant results. This paper utilizes millions of inspection results from in-use vehicles to compare OBDII and tailpipe emissions test outcomes.
My employer performs or manages the performance of vehicle inspection programs under contract to several governmental jurisdictions within the U.S.A. Therefore the process by which conclusions were reached for this paper involved management and/or oversight of vehicle inspection operations as well as collection, processing and analysis of millions of inspection records. Data analysis includes comparisons of initial inspection pass/fail rates, as well as post-repair retest pass/fail rates. Individual model years, as well as model year groupings are compared. Also OBDII inspection failure modes are presented using analysis of vehicle Diagnostic Trouble Codes.
Several interesting trends are revealed from the data analysis. These trends provide some insight into the performance differences between OBDII and tailpipe emissions testing applied to in-use vehicle I/M programs. Additionally, insight is gained regarding failure mechanism trends as viewed from the perspective of OBDII.