A Mercedes Benz ML320 car with a mileage of about 80 thousand km and a M112 engine and automatic transmission equipped with a chassis of W163. The malfunction of the vehicle is that the engine fault lights suddenly appear on the dashboard while the vehicle is running, and the acceleration performance of the vehicle becomes worse after that. The connection diagnosis instrument is self diagnosed, and the engine system has two fault codes. The contents are as follows: "P2010-004, the three element catalytic converter rear oxygen sensor (G3/6) circuit breaker in the right column cylinder, the fault is present"; "P20D4, the load limitation function is activated". In view of the data flow, the signal voltage of the oxygen sensor at the back of the three element catalytic converter of the right column cylinder is 434 ~ 454mV, and the signal voltage of other oxygen sensors can reach 700mV. At this point, the two three way catalytic converters have reached the normal working temperature, 448 degrees. The above data shows the poor performance of the oxygen sensor at the rear of the three cylinder catalytic converter in the right column. Lift the vehicle and check the wiring harness connection of the sensor, normal. The oxygen sensor in the rear of the two three element catalytic converter is replaced, the fault code is cleared, the engine fault light is lit and the fault information is inquired after 10min. There is a fault code, the content is "P2083 -004, the left column cylinder three element catalytic converter rear end oxygen sensor (G3/5) circuit breaker, the fault is present". As a result, the original G3/6 is really damaged. The replacement treatment is carried out, and the failure is completely eliminated. The M112 engine is a V6 engine with 4 oxygen sensors with two steam pipes: the left column cylinder three yuan catalytic converter front oxygen sensor (G3/3), the right column cylinder three yuan catalytic converter front oxygen sensor (G3/4), the left column cylinder three catalytic converter oxygen sensor (G3/5), the right column cylinder three element catalytic converter The rear oxygen sensor (G3/6). When the oxygen sensor is damaged, the engine control module sets the relevant fault codes, activates the engine fault lights, and limits the output of the torque. The fault of the oxygen sensor itself is difficult to judge. Sometimes it is difficult to determine the cause of the observation data flow. It can be checked by the replacement method, and the success rate of maintenance is high.