Drivers with new truck chassis but old engines that violate California air pollution control standards could face fines of at least $25,000.

Trucks are considered glider vehicles when older engines, transmissions, and rear axles are added to new truck chassis with frame, front axle, and cab. They are useful to the industry after accidents when the engine and associated components are intact but other parts aren’t.

“The problem arises when engines are salvaged from earlier model year vehicles, remanufactured, and installed in the glider kit,” a California Senate analysis of the bill, which passed Aug. 20, said. “Despite the...