A Lexus ES350 car with mileage exceeding 230 thousand km and equipped with 2GR-FE engine. Car owners reflect: the car has been air-conditioned for a period of time, when the switch is opened, the front of the engine is "squeaky" sound, the air conditioning switch off after all normal. Fault diagnosis: first start the car, open the air conditioning, the front of the engine really made a "squeaky" sound, which is similar to the inside of the belt grooves mixed with sand and pulley between the sound of friction. The engine belt was removed and checked. It was found that there were many grains of sand mixed in the belt slot, and there were several cracks. It was suggested that the owner change the engine belt. After changing the belt to open the air conditioner, the failure is still. After opening the air conditioner, it is explained that the engine load is increasing. Is the abnormal noise coming from the air conditioning compressor? According to past experience, the air conditioning compressor will not make any squeaks if it fails. Finally, turn off the air conditioning system, step on the brake, and hang up the D gear to increase the engine load. Sure enough, the squeak of the front of the engine appeared again. This indicates that the front abnormal noise has nothing to do with the air conditioning compressor. The stethoscope seemed to be the sound of the idler wheel Beside the generator, and then the idler wheel was removed from the other vehicle, and the squeaky noise still existed. His colleagues helped him to listen. He said it might be that the springs of the tensioner were loose and the sound of the belt was not strong enough. Because it is more troublesome to change the tightener, it takes half a day to remove some accessories such as engine, air conditioner compressor and so on. In order to prove the source of the abnormal sound to the customer, we must try it again. When the air-conditioned car is switched on, the noise still exists. The change is also changed, and no longer can be blindly dismantled. Finally, I would like to call someone else's colleague to see such a strange noise. My colleagues told me that I had met. Also changed a lot of pieces, finally the generator rotates well, the generator wheel is the clutch pulley, after the maintenance manual dismantled the generator, fixed the center of the belt wheel to confirm that the outer ring can only turn counter clockwise but not)! A clockwise rotation. If the result is not consistent with the regulation, replace the generator clutch pulley, after replacing the clutch pulley, whether it is the air conditioning or the brake to hang the D gear, the front of the abnormal noise, repair to the end.