Other Functions of Multimeters in Maintenance Work
(1) Leakage Current Testing Method
A multimeter is required for leakage current testing. The specific procedure is as follows: turn off all electrical loads in the vehicle and remove the ignition key. Use the current clamp accessory of an automotive multimeter to measure the current. If the reading is between 10 mA and 30 mA, the vehicle has no parasitic leakage. Conversely, if the reading is excessively high, a body electrical leakage fault is present.
Note that some vehicle systems still draw considerable current within 15 minutes after the ignition is turned off. If the measured current exceeds 50 mA, retest after waiting 15 minutes. If the current remains above 50 mA after this period, parasitic discharge is confirmed and further diagnosis is required.
Once leakage is confirmed, keep the current clamp fixed on the negative battery terminal. Remove fuses one by one while observing changes in the current reading. If removing a fuse produces no current change, the leakage does not occur in that circuit. If the reading drops back to the normal range of 10–30 mA (some vehicles allow normal values below 50 mA depending on the model), the leakage disappears, indicating that the circuit controlled by this fuse has leakage, grounding short-circuit or circuit faults.
(2) Quick Diagnosis of Electrical Components
The current measurement function can also quickly diagnose faults in many automotive electrical devices, such as headlights, audio systems, fuel pump relays, power window motors, alternators and other electrical components.
Taking the electric fuel pump as an example:
If the operating current reads 4.5 A, the fuel pump works normally.
Intermittent fuel cut-off is usually caused by poor circuit connections.
If the current is lower than 4.5 A, abnormal resistance, poor contact, or a dirty fuel tank may block the inlet strainer; the pump runs without load and shows reduced current.
If the current is higher than 4.5 A, the fuel filter is likely clogged or partially blocked, increasing the pump load.
Misdiagnosis is common in such conditions and should be carefully avoided during testing.
