VIN:LSGGA53F2EH×××××.
Driving mileage: 8020km.
Fault phenomenon: customers report that the warning light of engine instrument is on when driving, and sometimes it goes out; Moreover, the instrument will display four tire pressures, and even more strangely, four door locks will jump.
Continue to ask the customer for details: the frequency of flameout is about once every few days, and the door lock button occasionally beats inexplicably when driving; The instrument display is unstable, and it has been repaired several times in other 4S shops, and the fault has not been eliminated.
Fault diagnosis: technicians first verify the fault phenomenon described by customers, and no abnormality is found after trial operation. Check that the battery voltage is 12.67V and the charging voltage is about14.5V. The battery test is good, and ask the customer whether the battery has been replaced before. Later, during inspection, it was found that the power supply of the oil pump relay was equipped with high-power front lighting (as shown in figure 1), and the navigation system was installed outside the customer's factory. Therefore, it is suggested that the customer agree to remove the added components before debugging, which is beneficial to fault judgment. Let customers use it normally after disassembly,
Once again invited to the factory for inspection. No current fault code was found by the diagnostic instrument (as shown in Figure 2), and the gasoline pressure was measured. The gasoline pressure value is 400 kPa. Road test of connecting gasoline pressure gauge, no abnormality was found for a period of time. At the same time, check whether the power supply and grounding of the oil pump control unit are normal according to the circuit diagram (as shown in Figure 3).
Because it is a new car, it is considered whether the door lock wire (as shown in Figure 4) is submerged by the customer's film, resulting in intermittent short circuit. Check the relevant connectors of the door lock system, and everything is normal.
Because it is difficult to simulate and reproduce the fault phenomenon and the thinking is limited, it is difficult to have a clear diagnosis direction. It is still necessary to consider whether there is intermittent poor contact in the public power supply part of the electrical circuit.
Open the fuse box in the engine compartment and check whether the fuse is in good contact with the relay. When the power cord is shaken by hand for vibration test (as shown in Figure 5), the headlights of the vehicle light up inexplicably (as shown in Figure 6). Remove the fuse box, measure and check the power supply of fuse box, and check whether the power supply of fuse box X50A (as shown in Figure 7) is normal.
Fig. 5 Swing power supply
Fig. 6 Headlights are on
Figure 7 X50A Circuit
With doubts, I opened the fuse cover on the upper part of the battery again and unplugged the power cord, only to find that the contact part between the positive wire of the power supply and the fuse was ablated (as shown in Figure 8). It seems that this is the fault point that causes technicians to be confused. Re-grinding parts and troubleshooting.
Fault summary: judging from the final result of this case, it seems not difficult, but it happened that this kind of fault is the most prone to twists and turns. The reason lies in the randomness and uncertainty of faults, and most of the faults caused by power supply problems are long-term hidden dangers and difficult to diagnose. Therefore, when encountering such cases, I still hope to think more, explore more and observe more.