Symptom: Shanghai Passat sedan mileage of 40,000 km. The user reflects the car in the process of moving the front of the engine abnormal sound, continue to travel for some distance, the engine suddenly unstable operation and turn off, and then start no response.
    Troubleshooting: After receiving the car, with fault diagnosis VAG1552 detection found fault code display: Hall sensor G4 open circuit or short circuit. The Hall sensor signal provides a 1-cylinder compression stroke top dead center signal for the engine control unit for sequential fuel injection and knock control. If there is no Hall sensor signal, the engine can start running, but into the limp state, fuel economy and power will also be reduced.
    As the car has just travel 40,000 km, the mechanical aspects should be no problem. In view of the previous maintenance of Jetta had encountered due to the ignition timing is wrong and false positives Hall sensor fault code failure. Then remove the timing cover to check the ignition timing, with a wrench to turn the crankshaft but found that the fundamental turn does not move. Release the tension wheel check and found that the timing belt has been seriously gnawing teeth, the initial diagnosis of the valve has been the top.
    So remove the front bumper, condenser and water tank, check the engine timing belt drive mechanism, you can see the pump has been seriously leaking, the pump shaft bending and has been stuck. Timing belt is also the result of resistance to increase the gnawing teeth, which appeared when the chaos over the top of the valve, the engine does not have the fault. Check the cylinder head found that the third cylinder exhaust valve was broken card stuck in the cylinder head, the fourth cylinder exhaust valve is also a serious deformation, but fortunately the piston was not damaged.
    Users said that some time ago the engine often water, to the garage to check the replacement of the cylinder behind the water pipe three links, but did not find the water pump. The root cause of this failure is due to water leakage caused by the pump, for which the user asked the garage compensation for all costs and losses. After the customer file is recalled, it turns out that the user had repaired the leaky project a week ago. Asked the then the main workers, said the cylinder head to see the back of the obvious signs of antifreeze leakage, the replacement of the three links, but did not do the cooling system pressure test. From the pump stuck to see, the leak has been for some time, and proved that the last work of the garage is not fully in place. But the engine appears abnormal after the driver does not have timely parking check also have the responsibility, after consultation to remove all of its repair costs, other losses themselves.
    Failure analysis: In this to remind the majority of peers, Passat B5 leakage is a common fault, the cylinder head is the most common three-way fault point, while the water pump phenomenon also occurs. But the location of the pump is not easy to visual inspection, and often overlooked. Can be long-term leakage of water pump will lead to bearing stuck, will produce a serious fault when the top of the serious consequences of the valve. As the Passat B5 is equipped with overhead 20-valve engine, the repair costs can be imagined.
    In addition, the engine in the replacement valve do not rush to start, should wait 30min later, so that the hydraulic tappet and chain tensioner completely filled with oil, or will come to naught, the valve will be the top bend. So the maintenance of Passat B5 leakage must pay attention to whether the water pump is leaking, but also do not forget to check the expansion of the tank lid pressure valve can be in the pressure when the pressure relief, otherwise it will cause leakage of long-lasting illness.