What is parasitic draw
Parasitic draw is caused by a bad ground or a short in the electrical system which in turn causes an accessory to remain on while the car is turned off. There are some parts of the electrical system which do use power while the car is off and that is normal. For example the radio uses power to retain memory (for station presets and EQ settings) while the car is off.
The procedure for testing for this symptom is very easily done and requires only two tools.
What you will need
- 10mm socket wrench (or if you have aftermarket battery terminals like me, whatever tool is necessary to loosen a battery terminal)
- Digital multimeter aka. ammeter with alligator clips.
Lets get started
Step 1
Setting up the ammeter/multimeter.
First we need to make sure that the leads are plugged into the correct places.
This may vary from meter to meter but on my meter, the negative plug goes in the center and the positive lead goes into either the left or right plug depending on which function you want to use.
The right plug on my meter is for measuring volts, ohms and such while the left plug is used to measure AMPS which is what we are trying to measure here.
So make sure that your positive lead is plugged into the AMP plug on your multimeter. Consult the operating instructions if need be.
Here is how mine looks:
You also want to make sure that the meter is operating in AMP mode. Again, consult your operating instructions to insure that you are doing this properly.
Here is how mine looks:
Turn on your meter and leave it on for step 2.
Step 2
Now lets use our 10mm wrench to loosen the negative terminal on the battery....BUT DONT REMOVE IT JUST YET. Pull it up just slightly so you can clip one of your alligator clips(either one will do) onto the battery terminal under the terminal ring. Now clip your other alligator clip onto the ring itself.
The following 2 pictures show you how to clip onto the terminal and ring. I was not able to take a picture of me slipping it under the ring terminal because I didn't have an extra hand.
The reason we do this is so the car never actually looses power (do your radio presets will be preserved, etc)
Now you can completely remove the terminal, careful not to knock off the alligator clips. If this does happen it is no big deal, just simply clip them back on and you will have to reset your radio and possibly enter a security code.
Step 3
Reading the results.
Make sure that all the doors are closed and the keys are NOT in the ignition.
Take a look at that number that comes up in your meter. If it is any higher than 35 miliamps or 0.35 Amps, you have detrimental parasitic draw. If it is lower than that, then it is normal.
Here are some examples of values you may see.
When I checked mine, my car has almost no parasitic draw at 9 miliamps.
When I turned on the dome light, this is what the meter read:
When I had the dome light and the parking lights on:
As we all know, a dome light can kill a battery if left on long enough. The lower your parasitic draw, the longer your car can go without being started.
Step 4
What do we do with these results?
Well, if your draw is within acceptable levels, place the ring back over the terminal (without removing the clips until the ring has contact with the battery terminal) and tighten her down. You are done...celebrate.
If your draw is too high, you have more work to do. Leave everything as is. The next step is to see where its coming from. Start pulling fuses one at a time from both the interior and engine bay boxes.
After each fuse is pulled, check the meter to see if your draw drops to acceptable level. If it does, then that is a circuit that needs to be examined for shorts and loose grounds. There may be multiple faults, so keep pulling each fuse and checking for a drop in amps.
Once you have found all of the problem areas, check every wire associated with that circuit for shorts and/or loose grounds and fix them.
This should have you well on your way to fixing your battery drainage issue. If this article does not answer your questions, feel free to search the forums for pertinent info. If your question is still unanswered, post a new topic.
Good luck!
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Posted 10/3/2009 9:02:27 PM
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