This marine engine repair manual covers Volvo Penta models 230, 250, 251 DOHC, AQ131, AQ151, and AQ171. These internal combustion marine engines are engineered for reliable marine propulsion, with the 251 DOHC model featuring advanced DOHC technology. Volvo Penta is recognized for its commitment to quality and durability in marine applications, ensuring optimal performance for a wide range of boating activities. This comprehensive repair manual provides essential information for maintaining and servicing your Volvo Penta marine engine. It details routine maintenance procedures, engine removal and installation, and in-depth troubleshooting for critical systems including the fuel, lubrication, cooling, and electrical systems. Technicians and owners will find clear guidance on repair procedures, technical specifications, and advanced diagnostic techniques to ensure the longevity and efficient operation of these engines.