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Finding, Fixing Parasitic Draw

multimeter

A parasitic draw is when electricity is drawn from the battery even after the vehicle is shut down and all circuits should be shut off. You can think of it as being like when you've left the headlights on and the battery begins to drain because the engine is not running to replenish it. Unlike that scenario, however, the cause is not obvious and could be almost anything.

On older vehicles, built before standardized OBD codes were in place, finding a parasitic draw is a tedious process, but still do-able. We covered that last year in an article on How to Find a Parasitic Draw in older vehicles.

On newer machines, where multiple fuses (because of the requirements of OBD circuit sensing) are in place, finding the draw can be much easier. With the vehicle completely shut off and the key removed, after about ten minutes or so, all circuits in the car should be without power. Leaving the battery connected and taking proper safety precautions, you can test each fuse in the engine compartment individually. The top of most fuses have small probes where the tips of a multimeter can be placed to measure resistance across the fuse. Although their original purpose is to diagnose problems with the fuse itself, these points can also be used to unobtrusively test the circuit the fuse links as well.

If any of them are showing up on the meter, they have power and are thus the source of your parasitic draw. From there, finding the item causing the draw is a matter of just testing the circuit for a ground or other problem that could be causing the drain.

See it being done step-by-step in this video.

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