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Title: Heavy-duty on-road vehicle inspection and maintenance program

Principal Investigator / Author(s): Durbin, Thomas

Contractor: UC Riverside

Contract Number: 15RD022

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels


Despite substantial reductions in NOX and diesel PM emissions from heavy-duty vehicles (HDVs), they are still significant contributors to statewide and regional emissions of these pollutants. Because of their long service life, it is important that HDVs remain in emissions compliance throughout their entire lifetimes, and an HDV inspection and maintenance (I/M) program could be a way to ensure their compliance. A contract was awarded to the University of California, Riverside to evaluate and assess alternatives for a more comprehensive HD I/M program that could be implemented in California. This pilot study recruited 47 vehicles with 51 repairs at two commercial repair facilities, and measured emissions before and after repair. Vehicles were recruited for measurements when the check engine light was on indicating that the engine control module (ECM) had identified a repair or maintenance need. Substantial reductions in NOX emissions (75 percent at 30 mph and 46 percent at 50 mph) and PM opacity (43 percent) were observed for the fleet after successful repairs. Successful repairs of the 27 vehicles with the Diagnostics Message 1 (DM1) Malfunction Indicator Light (MIL) on, meaning that the vehicles had emissions-related malfunctions, resulted in even greater NOX emissions reductions. Analysis of more extensive two-year repair records indicated that 26 percent of the 2010+ vehicles had their check engine light on when they arrived at a repair facility for maintenance and/or repair, and 16 percent of the 2010+ vehicles had the DM1 MIL on. The average repair costs per vehicle were $1,803 for vehicles with check engine lights on and $2,037 for vehicles with the DM1 MIL on. Based on a review of the potential methods, the researchers propose that a revised HD I/M program incorporate both OBD and tailpipe methods, in a manner that is cost effective and provides cross confirmation between the different methods.


For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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