This manual covers John Deere W540, W550, W650, W660, T550, T560, T660, and T670 series combines manufactured during the 2012 and 2013 model years. John Deere has a long-standing reputation for producing robust and reliable agricultural machinery, and these combine models represent advanced harvesting technology, incorporating refinements from previous generations. This comprehensive Illustrated Factory Diagnostic, Operation and Test Service Manual is designed to provide in-depth information for the operation, maintenance, diagnostic, and repair of these agricultural combines. The purpose of this manual is to serve as an authoritative resource for owners, mechanics, and technicians. It offers extensive coverage of all major systems, including detailed theory of operation, schematics, component-level diagnostics, and repair procedures. Key areas include the engine, air intake and cooling, electrical systems with extensive detail on control units and CAN bus, drive systems, steering and brakes, hydraulic systems, main gearcase, and the cab operator station. Furthermore, the manual provides systematic troubleshooting guides based on observable symptoms and Diagnostic Trouble Codes (DTCs), alongside information on standard torque values and component identification, ensuring efficient and accurate service.