The Audi A8 6.0L car with a mileage of about 108 thousand km. User reflection: the car has a different belt when it starts cold. Fault diagnosis: (1) when the engine starts cold start, the belt has a squeaky sound, and when the steering time is changed or the load changes, the noise is serious. The belt and belt tightener are removed, the belt surface is smooth, no oil leaking is found, and other belt pulley has no stagnation. It begins to suspect that the belt is sands or other foreign objects, and the surface is too smooth after the belt slipping, and the belt is replaced when the load changes. After that, there was a noise. The belt tightener was replaced and the trouble was removed. (2) at the beginning, only the belt surface was too smooth. The belt tensioner does not leak oil, so it is considered that there is no fault, resulting in miscarriage of justice. The belt load is larger, the tensioner travel is smaller, and the tightening force is smaller, it is easy to cause belt slippage. Troubleshooting: replace the tightener.