The diagnostic methods for poor contact faults include: voltage drop detection method, resistance detection method, touch temperature inspection method, simulated vibration inspection method, etc. Poor contact of the ground wire After the starter is running, if the temperature of the ground wire of the battery is too high, and the ground point even burns red, it means that the ground wire of the battery is in poor contact. For old cars that have been used for many years, the grounding parts are oxidized or corroded to varying degrees. Even if it is a new car, because it has been stored for a long time in the open-air parking lot of the manufacturer or dealer, it is easy to cause poor grounding. You can measure the resistance value of the grounding point without power on. If there is resistance, it means that the grounding is not good. Use the simulated vibration method to check for suspected parts. You can gently swing the ground wire in the vertical and horizontal directions to simulate the vibration state when the car is running. Poor contact or wire breakage. If the fault reappears or disappears when a certain ground wire is moved, it means that the faulty ground is here.