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A Mercedes ML320 with a mileage of about 120 thousand km, a M112 engine and an automatic transmission, and a chassis model of W163. User response: the vehicle first appeared after the engine was extinguished, and the two air injection pump still operated, and finally became no longer running at any time. After receiving the vehicle: connect the fault detector to self diagnose, and there is no fault code stored in the engine system. According to the data, it is learned that the two air jet pump is powered by two air jet pump relays. Check the two air jet pump relay and find that the switch contacts are sintered together. The two air jet pump was removed and the rotor winding coils were burnt. Since the two air jet pump has a large working current, the two air jet pump relay is overheated, and the switch contacts are sintered together because of the high temperature, which eventually leads to the damage of the two air jet pump. Troubleshooting: replace the two air jet pump relay and the two air injection pump.