故障现象一辆2011年产丰田雅力士车,搭载4ZRFE发动机和4速自动变速器,累计行驶里程约为4万km,驾驶人反映该车在高速公路正常行驶时,自动变速器会从4挡突然降为3挡,且发动机加速无力,发动机故障灯点亮,为偶发性故障。故障诊断接车后首先试车,故障现象未重现。经询问客户得知,车速为60 km/h~120 km/h时故障容易发生,且故 Trouble A Toyota Yaris car in 2011, equipped with 4ZRFE engine and 4-speed automatic transmission, the cumulative mileage of about 40,000 km, the driver reflects the car in the normal highway driving, the automatic transmission will suddenly drop from 4 block to 3 block, and the engine acceleration weakness, the engine fault light is lit, as a sporadic failure. Troubleshooting After the first test car, the failure did not reproduce. Upon inquiry, the customer is informed that the fault occurs easily when the speed is 60 km / h to 120 km / h, and therefore