Engine manufacturers must install computer systems on big-rig trucks operating in California to diagnose and warn drivers of emission problems, according to an order issued by state air quality regulators.
The decision by the California Air Resources Board is the first such regulation in the United States for heavy-duty trucks.
The California measure is likely to encourage the U.S. Environmental Protection Agency to approve a similar rule.
There are an estimated 1 million to 1.5 million big-rig trucks traveling on California highways, each emitting more than 5 pounds of nitrogen oxide a day, the main ingredient of smog.
A diagnostic plan would cost approximately $130 per truck. The standards would be phased in for big-rig engines beginning in 2010 and fully implemented in the 2013 model year.