Research Projects

Project at a Glance

Title: Incidence of malfunctions and tampering in heavy-duty diesel vehicles. Phase I: Proof of concept.

Principal Investigator / Author(s): Miller, Wayne J

Contractor: UC Riverside

Contract Number: 01-340

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels


Emissions from on-road heavy-duty diesel (HDD) vehicles represent a disproportionate source of oxides of nitrogen (NOx) and particulate matter (PM). Malfunctions and tampering are important causes of elevated emissions and the incidence rates for nineteen categories are listed in the EMFAC 2000 model. However, the estimates for the incidence rates vary by more than 100% depending on the source of the estimate. In addition, the data are old and incomplete. This report details the work conducted under Phase I of this project, which was to compare the existing factors for tampering and malfunctioning for HDD trucks in the EMFAC model with those arrived at by the use of several new and independent methods and review of about 7,000 HDD truck records.

The approach or design of the new methods followed the life cycle and repair records of a HDD truck. For about 25% or 290,000 miles of its life cycle, the trucks are covered by a warranty and records are kept at ARB and EPA for specific causes of high emissions. From the analysis of 998 warranty incidents, we learned that most malfunctioning rates were in fair agreement with the values in EMFAC, except that the incidence rates of problems were much higher for fuel injectors, turbos and electronics. Being in fair agreement or higher gives cause for concern as the rates in EMFAC reflect the full life cycle and are expected to be low for the first 25% and increase dramatically for the last 25%. These data suggested that EMFAC may be underestimating the contributions from malfunctions. However, the driver survey and independent repair shop survey data, both of which are instantaneous measures of tampering and malfunction, correspond well with the EMFAC data.
Other data sources proved helpful in providing new insight on the remaining 75% of its engine life. For example, the analysis of 5,210 records for trucks that were inspected indicated that tampering was < 1%, so tampering is either not visible or is not there to begin with. Based on our observations when working along side the ARB experienced inspectors in the field and as most engines are designed with electronic controls, we do not think that tampering is a major contributor to emissions and, therefore, conclude that dedicating time to enhanced visual inspections would not be fruitful. However, our pilot work of electronic monitoring was the first to be undertaken in the field and the results yielded new insight about what information was available with proprietary download tools and how it could be analyzed, especially the issue of whether a off-cycle NOx chip was installed. Electronic monitoring should be pursued, as knowing if a reflashed chip is installed will become very important as the vehicles are modified to meet the new low-NOx standards.
A random roadside survey of 78 drivers about the problems with their trucks was undertaken with the resulting malfunction rates again in fair agreement with the values in the EMFAC table. The questionnaire for this form of a data collection is very important so that key information is obtained in an unambiguous nature in a short period of time. We suggest obtaining more surveys even thought the data is probably of a lower quality.


For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893

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