This service manual provides operational guidance for the common rail system (CRS) used in Isuzu Elf 4HK1 and 4JJ1 engines, detailing applicable vehicle specifications, system components, and diagnostic trouble codes. It includes information on supply pumps, injectors, control systems, and exhaust gas regulation systems necessary for compliance with Euro 4 and Euro 5 guidelines. Compliance with North American exhaust gas regulations is also addressed, especially regarding the use of diesel particulate filters for specific model years.