SACRAMENTO, CA — Diesel engine manufacturers went to court on April 21 to try to block stricter pollution standards set to take effect in a week, arguing state regulators reneged on a $1 billion legal settlement in 1998, according to the Associated Press. Judge Loren McMaster, in a tentative ruling before he heard arguments, denied manufacturers' request that the initial April 30 compliance deadline be delayed while their lawsuit proceeds against air pollution regulators, according to the Associated Press. No final order was immediately issued in the case. The California Air Resources Board has said that strict pollution standards adopted in December are needed because a voluntary program promoted by manufacturers wasn't working. The board's regulations require owners of diesel engine trucks to remove 'smog defeat' timing devices that allow the engines to meet pollution requirements when trucks are inspected — but exceed the limits when trucks travel at highway speeds. The regulations apply to an estimated 300,000 to 400,000 vehicles licensed in other states that drive through California, as well as 58,000 California-licensed trucks. The board has said removing the devices from California-registered trucks alone would trim air pollution the same amount as removing 1 million cars from the state's highways, according to the Associated Press. Caterpillar Inc., Cummins Inc., Mack Trucks Inc. and Volvo Powertrain Corp. argued they've already paid the state $37 million in civil penalties and other costs. Recalling the trucks simply to replace the devices would cost truck owners millions of dollars in downtime costs for the replacement and new inspections if they comply, and $300 to $800 in penalties for each truck if they don't, the companies said in the Associated Press article. In a 1998 settlement, manufacturers were required to replace the defeat devices only when the heavy-duty engines needed major overhauls, which happens far less frequently than regulators had expected. A year ago, the air board agreed to a voluntary plan for the industry to reach 35 percent compliance by last November and 100 percent compliance by 2008. The board said, however, only about 18 percent of the California-licensed vehicles had the upgrades by November, necessitating the mandatory regulations, according to the Associated Press report.