The mileage is about 72 thousand km, which is equipped with 2011 New TOYOTA crown cars of the 3 GR-FE engine. Users reflect: when the engine is running, the engine fault lights are bright, and the engine fault lamp lights up when the vehicle runs 40 ~ 50km, and the skid indicator lights up. When the fault occurs, the vehicle is in the deceleration condition. Failure analysis: the customer came to the factory and detected by IT-II detector. It found that there was P2159 fault code in the engine control system, which was a continuous dilute fault code for the 1 cylinder side 1 air fuel ratio sensor. At the same time, the engine control system fault is detected in the ABS control system. At that time, it was thought that the engine was faulty. Therefore, the fault code should be removed so that the customer could leave the factory. But on the morning of second, customer calls said that the engine fault light was on the bright side, and the mileage of the last light was about 50km. In the afternoon, the customer came to the factory to test, and the trouble code was P2195. After collecting the freeze data, the A/F air-fuel ratio active test is carried out and the air-fuel ratio sensor changes normally. The road test was carried out, and the data flow at the time of failure occurred in the final inspection mode. Through the analysis of the data flow, it is found that the voltage of the air-fuel ratio sensor is 4.99V at the time of the failure code, as shown in Figure 1. Therefore, the reason for the failure is that one is the abnormal air-fuel ratio sensor, the two is the bad engine ECU. After the field guidance of the personnel in the technical room, through the road test and the exchange between the air-fuel ratio sensor, the fault code is confirmed to be P2197 (the 2 cylinder side 1 air fuel ratio sensor is always thinning), indicating that the fault is caused by the air fuel ratio sensor abnormal. Troubleshooting: replace the 1 cylinder side air fuel ratio sensor. Road test, fault code no longer appear. Fault revelation: for the failure of the new car, it must be checked strictly according to the requirements of the maintenance manual, especially the active test mode in the book, which is the best way to reappear the fault. Failure review: new models, new parts, problems, indicating that there are still some problems in the manufacturing process. It is necessary for the manufacturer to strictly control the quality, especially the new model. In the early stage and the production stage, every link is very important, otherwise, if the problem occurs, the user is doubtful about the quality of the vehicle. I don't think the manufacturer would like to see such a result.