A Mercedes ML320 multifunction vehicle with a mileage of about 120 thousand km and a M112 engine and automatic transmission equipped with chassis W163. The car malfunction is: after the engine is shut down, the two air injection pump still works. After receiving the car: after inspection, it was found that the two air jet pump was overheated for a long time and pulled off the plug to stop it. The connection diagnostics is self diagnostic, and the engine system has no fault code. 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 burned together. The two air jet pump is removed and the rotor winding coils are broken without repair value. At this point, the cause of the failure is clear, the two air jet pump working current causes the two air jet pump relay overheating, the switch contacts are burned together because of the high temperature, resulting in the damage of the two air jet pumps. Replace the two air jet pump relay and the two air injection pump. The trouble is completely eliminated. Her circle 8 two air ejection systems belong to the selection system. The main components include two air jet pumps (M33), two air jet pump relay (K28), two air jet shutoff valves, two air jet conversion solenoid valves (Y32), etc. The two air injection pump is installed in the front part of the engine, and its function is to pump air into the exhaust manifold and burn with the exhaust gas to achieve the purpose of noise reduction and purification. The two air jet pump relay is used to provide the working voltage to the two air injection pump and the two air injection conversion solenoid valve. The two air blast shut-off valve has two valves located on the left and right valve chamber covers. The two air injection conversion solenoid valve is located under the two air jet pump, and the three pipe ports are connected with the intake manifold, the air line and the two air jet pump cut valve lines respectively. The fault is typical. When there are two frequent failures of the air injection pump, two air jet pump relays must be replaced.