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Fault diagnosis: the fault car enters the factory to repair, the temperature of the engine coolant is high, the water pipe has been expanded at high temperature, the water pipe has been cracked, and the cooling liquid is added after the replacement of the water pipe. The starting engine check found that the high temperature of the cooling fluid is that the temperature of the cooling liquid can not be opened. The fan works normally and the coolant temperature is no longer high. The customer also asked to check the circuit, said the horn was not loud and the dashboard indicator was not lit. It was found that the fuse of the horn and the fuse fuse of the dashboard, the horn returned to normal after replacing the fuse, and the dashboard light was also bright, but it was found that the engine fault warning lamp, the ABS warning lamp and the airbag warning light were not extinguished after the car started, and the car was not lit before we came to the factory. So we connect the golden Pentium color Saint decoder into the engine system, read the storage fault code "deflagration sensor fault", check the circuit to find the deflagration sensor plug off, plug the plug. According to past experience, this vehicle will not cause fault due to deflagration sensor failure, warning lamp will not extinguish after starting. Again, it was found that the owner inadvertently used the spare fuse inside the fuse box and filled the fuse box in the fuse box, so that the engine electronic control system, brake antilock system and the airbag system were in the self diagnosis state. After closing the ignition switch, pull out the fuse on the fuse socket and start the engine test again, and result in the ABS warning light and the airbag warning light or the alarm. Once again connect the golden Pentium color decoder into the engine system, read the fault code as "normal system". Engine system troubleshooting. Then enter the ABS system, read the storage fault code "left rear wheel accidental fault", check found that the left rear wheel ABS sensor plug water has been corroded, cleaning terminal after loading, after clearing the fault code read as "system normal", ABS troubleshooting. The air bag system using the decoder shows that the automobile electronic control system does not respond; check the airbag electronic control system power supply fuse (red fuse socket) to terminal 5 (Bai Hong) connection well, terminal 6 hash wire (brown) grounding well, terminal 9 (K line, green) to diagnosis socket connection well, terminal 7 (Hong Bai) gas The control line of the capsule warning lamp is good. Check the connecting line of the main and auxiliary airbags is good (disconnect the main and auxiliary airbag connectors). Because the decoder can not enter the human airbag electronic control system, a short circuit resistor (2.5 omega) is used to replace the main and auxiliary airbag plugs to replace the detonator, but the fault warning lamp is always bright. In this way, it can be concluded that the electric control system circuit and the auxiliary air bag should have no problem. Cut to the control line of the fault warning lamp, the fault warning light is extinguished. This is basically determined to be a fault of the airbag electronic control system. All the time the output signal causes the air bag warning light to be brighter. After replacing the air bag control unit, the engine is started, the air bag warning lamp is extinguished, the electronic control system of the air bag is connected with the golden Pentium color Saint decoder, and the fault code is read as "normal system", so the fault is completely eliminated. Maintenance review: Hongqi century star adopts three sets of electronic control systems, engine VG20E uses Nissan products, ABS is the MK20-1 anti lock braking system commonly used by Volkswagen, the airbag is a Daewoo Corp product, can use the original factory diagnostics of three companies to test, also can use China's Jin Pentium, repair car Wang and other comprehensive vehicle type diagnostic instruments are tested, but three sets of diagnostic procedures for electronic control systems and different diagnostic plugs must be installed. The author ruled out 7 failures: up water pipe expansion (due to high coolant temperature), high coolant temperature (because of a thermostat), no loudspeaker (because fuse fuse), the dashboard indicator light is not bright (because fuse fuse), deflagration sensor fault code (due to plug off), three warning lights are not extinguished after starting ( A fault (due to plug rust), a ABS warning lamp alarm (due to ABS control unit damage) is found because the fuse is wrongly inserted into the fuse for a long time. I think the author's technical skills are very strong, the diagnosis is correct and the inspection is in place. The author, when measuring all wires of the airbag electronic control system, simulated the resistance of the detonator with a resistance of 2.5 Omega resistance, verified that the circuit of the airbag warning lamp did not fail. Finally, it was determined that the electronic control system of the airbag had a fault. In the case that the electronic control system circuit was no problem in the peripheral operations, the attack was broken to the core area. There are problems in the control system of airbag. One of the insufficiency of the case: after the vehicle enters the factory, the business personnel should ask the owner of all the failure phenomena, negotiate with the owner and repair the project after the pre inspection, and then open the car repair Commission, wait for the owner to agree to the maintenance project and sign the service by the owner and the salesman, so as to avoid the maintenance of the maintenance project. The problem of disagreement in the repair fee. This will not only protect the interests of both sides in law, but also make maintenance personnel aware of all the fault phenomena reflected by users. The car seems to have completed a fault owner and then put forward the next fault, and the maintenance of the fault found in the repair do not know whether the owner after the repair, as if the repair plant juice user vehicle maintenance full power. This is not a method of standardizing a repair plant. Every standard enterprise should establish various working processes and regulations such as factory maintenance, quality inspection, quality guarantee, spare parts guarantee and so on. These belong to the two level documents of the IS09000 quality certification system, and the quality management manual is the first level of the system. Insufficient two: in order to verify whether the air bag warning lamp is caused by a circuit fault, the method of cutting the warning light wire is not advocated, even the old vehicle can not easily cut the wire, which is seriously barbarous operation. The normal method, such as the airbag warning lamp, is controlled by the electronic control system. It can be used to verify the failure of the control circuit of the internal warning lamp in the electronic control system by the method of pulling the plug of the air bag electronic control system.