Fault diagnosis: computer detection engine system failure code, test car found in a set speed 80km/h driving, gas speed up, the speed of oil after slowly dropping to set speed will continue to drop to about 60km/h, and then the speed will slowly rise to 80km/h, not every time. First of all, it is doubtful whether the throttle is dirty or not, then clean and match first, then tighten the throttle plug. There is still a failure in the test. In communication with the owner, it is found that the car has changed the front wheel bearing in other places, so it is doubtful whether the speed sensor is affected. The speed sensor data block finds that the speed of the two front wheels will change at a set speed, and the back wheel does not have this phenomenon in the range of 3km. Troubleshooting: replacement of front wheel bearing test run, troubleshooting.