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A mileage of about 184 thousand km, the 2004 Volkswagen Santana car equipped with BKU engine. After the ignition switch is disconnected, the engine can not immediately extinguish, and wait for about 1 min to extinguish it. Fault diagnosis: test car discovery, switch on the ignition switch, fuel pump work all the time; disconnect the ignition switch, fuel pump is still working, from which the fuel pump power line or control line is inferred. Check the fuel pump power line, all normal; check the fuel pump relay (J17) control line, found that the control line should be connected to the engine control unit (J220) terminal T121/65 line, but directly connected to the body directly. Troubleshooting: put the iron wire in the fuel pump relay control line to the engine control unit terminal T121/65 and test the car. After the ignition switch is disconnected, the engine is extinguished immediately. Fault analysis: the conditions of the engine work are not limited to the fuel pump supply, but also require the ignition system to participate in the work. Then, in this case, why can the ignition system continue to work after the ignition switch is disconnected? The engine control circuit shows that the power supply of the ignition coil and the power supply of the fuel pump relay control circuit are all controlled by the power supply relay (J271). It is found that the ignition switch is connected to the ignition switch, the power supply relay is absorbed, the terminal 6/87 has 12V voltage output, the ignition coil, the fuel pump relay and so on are supplied, and the ignition switch is disconnected and the relay contacts will not be disconnected immediately, but the ignition switch is disconnected after the ignition switch is disconnected, and the ignition coil and the ignition coil are disconnected, and the ignition coil and the ignition coil are disconnected, that is, the ignition coil and the ignition coil are disconnected, that is, the ignition coil and the ignition coil are disconnected, and the ignition coil and the ignition coil are disconnected after the ignition switch is disconnected. The power supplied on the fuel pump relay will not disappear immediately. Under normal circumstances, how does the engine stop immediately after the ignition switch is disconnected? The inference is that after the ignition switch is disconnected, although the power supply relay can delay the operation for about 1 min, the fuel pump relay will immediately cease to work. In order to verify the controlled state of the 2 control coil loops of the power supply relay and the fuel pump relay in the engine control unit, tens of thousands of tables are connected in the 2 control coil circuits respectively. Starting engine, 2 control coil circuit all current exist; disconnect the ignition switch, power supply relay control coil circuit still has current, about 1 min disappear, and the fuel pump relay control coil circuit current with the ignition switch disconnect immediately disappear.