Battery Always Dead How to Perform a Car Truck Parasitic Draw Test

Have you ever installed a new battery, maybe you also installed a new alternator, and then a day or two later this happens, nothing. Chances are, you have a parasitic draw and that's what's draining your battery. The easy way to look at this is you probably have a light on or one of the modules is staying awake and drawing current from the battery. Now, I'm going to show you how to test for that.

The first thing you want to do is hook up a battery charger, charge that battery up, get it up to par or you're going to be going in circles. For newer vehicles or batteries with a lot of modules what you're going to need is a battery shutoff tool or a parasitic draw tester. That's what this tool is. Basically, this goes in between the battery and the negative cable so that you can shut this on and off. What you do is hook it up to the battery. Take the vehicle for a ride, turn on all the electronics that you can think of, the radio, the heating and air conditioning, cruise control, everything. That way when you get back from your road test, you can hook your meter up to one end and to the other end and open this switch without disturbing any of the modules.

The next step, we want to be able to access all the fuse panels. There's a fuse panel right here, pull the cover off. And there's another fuse panel right here. If there's any other fuse panels in the car, be able to access them and then, you want to go to all the door latches and just latch them. That way the dome lights stay off, if the vehicle has dome lights that are through the latch. Sometimes you might have a dome light switch, those are going to be a little harder, you're gonna have to find a way to push those down, but do that to all the doors. Now, let's hook up the meter. Every meter is a little bit different. You're probably going to have to move the power wire or the positive wire to the AMP setting. I'm going to put it on the10 amp max fused, and then the common ground, we're gonna switch the meter to milliamps. And then we can hook one of these on one side, doesn't really matter which side is which, and then one on the other side.

Now, before you open the switch up, you want all the modules to go to sleep. Basically, modules are still talking to each other and doing their thing, that's going to put a draw on the battery. That's normal. So older vehicles takes about 10 minutes for those to go to sleep, newer vehicles could take up to an hour, so wait a little bit and then we'll open that switch up. Okay, this vehicle is hooked up as if we just open that switch and there's our reading right now. Now, this is seven... Well, it just dropped down. So one of the modules must have just shut down but that was 700 milliamps. And now we have 400 milliamps. What we want to see is less than 30 milliamps. So what we could do now is wait a couple more minutes, maybe wait another 10 minutes and see if this goes down, or even an hour, up to an hour and see if it changes. If it doesn't then we got to go a little bit further.

All right, so here's a good example of a light being left on. If you have the light on on the glove box, and I go to turn it off, as you can see, the number went drastically down. If I let it up, turn the light back on, then it goes back up. So the next step to find out where that draw is coming from, we're going to pull one fuse at a time. Now, if you have an idea of where you think it might be coming from, like if you think it's coming from the radio, you could go and find the radio fuse, pull that first or you could just go each individual fuse, just pull one at a time, and then check your meter and if it goes down, then that's probably the circuit that you're gonna have to go look at and see what's staying on.

Now, when you put the fuse back in, depending on what circuit it is in, it may turn the module on and you may have to wait another minute or two, if you see that it spiked above where you were before, like we were at 400 milliamps. If it goes to 1 amp or 1,000 milliamps, then you're probably gonna have to wait another 10 minutes for it to power down before you pull the next fuse. And it's never a good idea to just pull all the fuses out because it's such a pain to have to go back and put them back in afterwards. One thing to mention is very important while you have this meter set up like this, that you don't open any doors that have been left closed, or unlatch the doors that you latch before, because you could potentially blow the fuse in the meter. They're pretty expensive.

I'm going to pull a 30 amp fuse, pull that out, it dropped down to below 30 milliamps, which is awesome. So now I found the circuit that I need to look for. So that circuit happens to be to the GPS navigation CD holder. So what I can do is put that fuse back in, and then go over to this, disconnect this. And if my draw goes out, then this is the cause of the draw, something's keeping this awake, whether there's an internal fault in this unit, or whether something else is telling us to stay on, that's where the draws and now I can fix the system.

I hope this video helped you out. I know parasitic draws can be difficult sometimes, just take your time, you can do it. If you enjoyed this video, please subscribe to our channel. Make sure you ring that bell, turn on all notifications so you don't miss any of our videos.

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