The paper details an analytical redundancy fault diagnosis method of automated mechanical transmission (AMT) control system. The basic principle of AMT is depicted. After concisely introducing the models of engine, gear box and clutch, which are used to provide redundant information, the diagnostic logic is illustrated in detail. The information redundancy in the local models of the powertrain and the structure logic relations among the assemblages is used to detect and diagnose the faults of the sensors, the actuators and the unit assemblages of the AMT system. The fault codes and fault process measures are listed out.