Some functions of the multimeter have not yet been fully utilized by users.
1. The current test function is not taken seriously
For a long time, the current test function has been ignored in maintenance. With the emergence of more and more new technical equipment on cars, sometimes effective diagnosis cannot be made without current testing. For some leakage situations that are difficult to determine, such as: ① The battery plates are short-circuited or oxidized and fall off, resulting in self-discharge and loss of power. ② The grounding of electronic components causes leakage. For example, the insulation layer of a certain line in the circuit is aging or falling off, causing contact with other metal parts. In these situations, the current testing feature of a multimeter can come in handy.
(1) Leakage test method
When conducting a leakage test, you need to use a multimeter. The specific method is as follows: turn off all electrical equipment in the car, remove the ignition key, and use the accessory current clamp of the car multimeter. If the current flowing through the meter is 10 to 30mA, it means there is no leakage in the car. On the contrary, if the display is too large, it is considered that there is a body leakage fault. It should be noted that some systems will absorb a lot of power within 15 minutes of turning off the ignition switch. Therefore, if the current measured is above 50mA, the test should be repeated after 15 minutes. If it is still above 50mA at this time, it means there is a discharge phenomenon and further diagnosis is required. When it is confirmed that there is leakage in the vehicle body, keep the current clamp clamped on the negative terminal of the battery. You can remove the fuses one by one while observing the changes in the current value of the instrument. If the number displayed on the meter does not change after removing a certain fuse, it means that the leakage does not occur in this circuit. If the value displayed on the digital clamp ammeter returns to normal 10~30mA (the normal value of some cars is below 50mA, the specific value depends on the model), it means that the leakage phenomenon has been eliminated, which means that the fuse control circuit has leakage, grounding or short circuit problems. exist.
(2) Rapid diagnosis of electrical equipment
Using the current test function, you can also quickly diagnose and detect the reasons why electrical devices such as headlights, speakers, oil pump relays, electric door and window motors, and generators are not working. For example, for the detection of the electric fuel pump, if the working current I=4.5A, the oil pump works normally. If there is a fuel cutoff, it is caused by a broken circuit connection; if the working current I<4.5A, it means there is a resistance in the circuit or The connection is broken, or the fuel tank is too dirty, and the oil pump cannot absorb oil after impurities block the oil inlet filter, resulting in a no-load current; if the operating current I>4.5A, it means that the fuel filter may be blocked or partially blocked, causing the oil pump load to increase. . In this case, misjudgment of the oil pump is very easy to occur, so attention should be paid during detection.
