How do you isolate an unidentified draw of current from a car's electrical system?

Question

I have a 1991 honda CRX. It mysteriously drains the battery even thought nothing is left "on". What can I do?

Answer 1

The "remove each fuse one at a time" will work but there are a few things that can confuse this process.

First, in modern cars there are a number of circuits that draw current all the time. For example the car computer, the radio (so it can remember what stations you programmed) and the alarm/remote door system (if your alarm system has a blinking LED, you will see the current draw change as the LEB blinks on and off).

To isolate these you really need to use a meter not a light so you can determine the amount of reduction of current draw when you remove a fuse. If you remove one of these fuses and see the current go down a little, that is normal. Remove the fuses for the circuits I mentioned then see if there is any current draw. If there is, continue removing fuses. If you see another current drop, you have to decide if it is a circuit that should normally always draw current or not.

Note, an undersize battery will not last long because of this continuous current draw. Also, a weak battery will die pretty fast because of this continuous current draw.

Second, there are some circuits that are not routed through the fuse box so there could still be current draw even with all the fuses removed. There are a few on most cars. I once had a bad rectifier in the alternator. It was drawing current all the time but since it didn't go through the fuse box, the fuse method didn't show anything. I finally did track it down and replace the rectifier module.



Good Luck.

PeteC

Answer 2

Each time you park it for a couple days, remove one of the fuses until you find the fuse circuit that's draining the battery down. It's a lot faster if you've got an inexpensive Volt Ohm Meter (VOM) that you switch to the DC Amperes (Amps) position and insert between one battery cable terminal and it's battery terminal connection. The DC Ammeter should read less than 1/4 Amp (250 Milliamperes) when all the lamps in the car are off and the cars been parked for awhile. Once you know which fused circuit is drawing the excess current, you can start disabling things on that particular circuit. Sometimes alarm systems will turn out to be the problem.

Answer 3

You'll have to buy a test light.
Disconnect the negative battery terminal and connect one end of the test light to the cable and the other end to the battery. turn key off, close doors and check to see if test light is lite up.
If it is, start pulling fuses til the test light goes out, and that will be the circuit where your draw is.
Find out what's on that circuit and follow the wiring to check for short. If no short found, unplug each electrical plug in that circuit until light goes out and you'll find the electrical device short.

Answer 4

Locate a DC milli-amp meter and pull the fuses one at a time until it zeros out. Make sure your battery is OK first, with a load check at your mechanic. It could just be a slight short in the battery, or the case may be dirty enough to draw the battery down.

Answer 5

Remove one of the battery terminals,,and put a test meter between the terminal and the battery post you disconnected from.
then start pulling fuses,,one at a time and see if the voltage read changes, when you have found the fuse which causes the voltage to drop on the meter,,at least you will have an idea where to continue searching from.
other than this,,,you could have a battery switch installed,,which will disconnect the battery all together while your not using it.

Answer 6

inclusive of your Multi meter set to the Amp putting do because the others stated pos or neg area of the battery isn't major, get rid of fuses as stated to discover circuit at fault, if no fault is found disconnect alternator leads, as a foul diode in the alt itself often is the reason behind a parasitic draw. also keep in mind that more moderen vehicles will continuously prepare some draw with the aid of ECM and different digital instruments, a million amp is mostly the norm. so that you're going to under no circumstances see a nil analyzing, and an extra effective ingredient, at the same time as your checking your fuses and your door is open you want to make confident your dome and interior light fixtures are off, Duh.

Answer 7

first you will need a 12 volt test light, unhook the negative battery cable and put the light between the battery and the cable it should not light , if it does you do have a draw.
now you need to find your main fuse box and pull the fuses one at a time when you pull one that makes the light go out that is the circuit that has the draw.find out what is on that circuit and us a process of elimination to track down your draw

tony

Answer 8

check and make sure the light under the hood isnt on, if applicable of course i have seen this many a time but the test light fuse trick does it everytime, the only thing is if you pull a fuse and the light goes out you get to figure what circuit is powered by that fuse. also another trick, if the test light stays bright just touch the negative cable to the negative terminal it makes the computor shut off or something like that