Abstract: Aiming at diversity of faults for Dongfeng Peugeot 408 multiplex transmission network, this paper analyzes the basic structure of transmission network, presents multiplex transmission line terminal resistance principle and detection method.CAN high speed data bus which may occur circuit breaker in the data bus, short-circuit between CAN_H and CAN_L data line, CAN the data bus to the positive or negative electrode short-circuit fault are tested and analyzed by using Dongfeng Peugeot special oscilloscope PPM, .This test is effective in the fault discrimination for Peugeot multiplex transmission systems.