How to Find a Parasitic Battery Drain

Step-by-Step Guide

1. 1

   Step 1: Remove the negative side battery cable from the negative battery terminal.

   The meter needs to be able to read at least 2 or 3 amps for this test to work.
   
   Connecting the red wire to the mA input on the multimeter won't work and could damage the meter. , Wait a few seconds to several minutes for the car to go into sleep mode — i.e. when you make the contact with the ammeter, the car's computer systems "wake up." After a bit of time they will go back to "sleep."
   
   , Pull the main fuses (higher amp ratings) last.
   
   Perform the same steps on all relays found in the fuse panel.
   
   Sometimes relay contacts can fail to release, causing a drain.
   
   Be sure to observe the ammeter after pulling each fuse or relay. , The fuse that reduces the drain is the draw.
   
   Consult the owners' manual or service manual to find what circuits are on that fuse. , Disconnect each lamp, heater, electrical device one at a time to find the drain. , The ammeter will tell you exact numbers. , The alternator can sometimes have a shorted diode that can cause amps to flow through the alternator's power cable and through the shorted diode and into the case and through the bolts and back to the negative battery terminal.
   
   This will drain a battery in a hurry.Make sure to read the ammeter before and after unplugging your Alternator.
2. 2

   Step 2: Connect the black wire to the com input on a multimeter and the red wire to the 10A or 20A input on the multimeter.

3. 3

   Step 3: Attach a multimeter (set the dial on the multimeter to measure Amps as per multimeters instructions) between the negative cable and the negative battery post.

4. 4

   Step 4: If the ammeter is reading over 25–50 milliamps

5. 5

   Step 5: something is using too much battery power.

6. 6

   Step 6: Go to the fuse panel(s) and remove fuses

7. 7

   Step 7: one at a time.

8. 8

   Step 8: Watch for the ammeter to drop to acceptable drain.

9. 9

   Step 9: Check each device (circuit) on that fuse.

10. 10

    Step 10: Repeat steps 1 & 2 to test your repair.

11. 11

    Step 11: Try unhooking the big wire from your alternator.

Detailed Guide

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