THOUSAND OAKS, CA – J.D. Power and Associates has ranked the Caterpillar C-15 highest in customer satisfaction with vocational heavy-duty truck diesel engines, according to a recently released study on Heavy-Duty Truck Engine/Transmissions. A Caterpillar engine has ranked highest in the vocational segment five consecutive times. The J.D. Power and Associates study measured customer satisfaction in three vital engine factors: engine quality and warranty; engine performance; and engine noise and vibration. The study was based on responses from 2,429 primary maintainers of two-year-old Class 8 trucks. The Cat C-15 received high satisfaction ratings on six of the eight questions that make up the Engine Index. The Caterpillar C-12 follows the C-15 in the rankings with strong scores across all three customer satisfaction factors. The study examined engines in 2003-model year trucks, which were the first affected by the emissions regulations enacted in Oct. 2002 that raised diesel engine emissions standards.