How to test parasitic draw that causing overnight drains on the car battery? Current draw or parasitic draw is the continuous drawing of power from your car battery even if the engine is turned off, this draw will discharge your battery faster than normal.
How to test for current draw
1. Conduct the test on the negative side by removing the battery cable from the negative battery terminal. Set the multimeter to the current measurement setting. Make sure that the engine is turned OFF.
2. Connect the multimeter in series with the battery to complete the circuit. The negative test probe of the tester to the negative battery cable then the positive probe of the tester to the positive battery terminal as shown in the illustration.
3. Read the measurement indicated on the tester, if the reading is zero there is no draw, if the reading is greater than zero (Ampere > 0) then there is a current draw. A draw of 2.0 A is enough to cause the battery to drain overnight.
How to identify the circuit causing the draw
First, locate the fuse box, one fuse box is located in the engine compartment, usually near the battery. The other fuse box is located inside the cabin, usually, it is located on the driver's side underneath the steering wheel.
Set the multimeter to voltage measurement setting then measure the voltage across every fuse as shown in the illustration.
If the measurement is,
0 – The circuit is OK and there is no draw.
OL – The circuit is OPEN, check for the busted fuse.
Greater than zero (> 0) – This is the circuit that draws current from the battery, check if there is a load that functions which causes draw.
Using Multi Tester to Complete the Circuit of Alternator
Remove the B+ terminal of the alternator. Make sure that the engine is turned OFF. Observe the reading on the ammeter, if the reading is zero then the circuit is okay or the Alternator is Okay if the reading is more than zero the diodes on the alternator are shorted.
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