This manual covers the Monaro and GTO models produced between 2004 and 2006. Built on the Zeta platform, these rear-wheel-drive coupes are celebrated for their American muscle car styling and performance, enhanced by Australian engineering and chassis tuning. Available with either the 5.7L LS1 V8 (2004) or the more powerful 6.0L LS2 V8 (2005-2006), and featuring a choice of a T-56 6-speed manual or a 4L60E 4-speed automatic transmission, these vehicles offer a compelling blend of power and driving dynamics. With 5-star front impact safety ratings and standard traction control, the Monaro/GTO represents a significant entry in the performance grand tourer segment. This comprehensive workshop service repair manual provides detailed guidance for all models, engines, trim levels, and transmission types. It covers essential maintenance procedures, including scheduled servicing, fluid checks, and filter replacements, alongside in-depth repair instructions for all major systems: powertrain, chassis, electrical, and body/interior. The manual facilitates troubleshooting with diagnostic procedures and fault code interpretation, enabling owners and technicians to maintain and repair the vehicle effectively. Its extensive scope ensures that everything from basic upkeep to complex component overhauls and electrical system diagnostics is thoroughly explained, empowering users to keep their Monaro or GTO in optimal condition.