Mitsubishi Montero & Montero Sport This sport utility vehicle offers more size than the other Mitsubishi SUVs, but manages to keep a sporty look and comfortable feel, unlike many larger SUVs.

How to find a parasitic draw - 2001 Montero Sport 3.0 liter

Old 11-15-2018, 10:03 AM
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Default How to find a parasitic draw - 2001 Montero Sport 3.0 liter

Hi all,

I am working to locate a parasitic draw and thought I would document my steps for other wrench spinners' use. I would appreciate any comments to try to collect all of the wisdom on the subject in one place if possible.

Background of vehicle: I bought the vehicle recently in poor condition, very oily under the hood, quite rusty under the hood from New Jersey salty winter roads. Odometer 137,000 miles. The vehicle was a daily driver for the previous owner, and then had been parked for almost a year.

Symptoms: My battery died after leaving the dome light on a couple of times. I used a battery charger and charged the battery and determined after charging it overnight that it would not hold a charge (it wouldn't charge up to 12.4 volts or higher, and it discharged again in an hour or two). So I replaced the battery. But the new battery would drain overnight. I charged the battery to 12.4 volts overnight, and it did it again.

So I looked for a parasitic draw--where something in the vehicle is continuing to drain the battery after the key is off and all lights etc. are off.

Tools: A good multi-meter.

Ways to confirm you have a draw: There are several:

(1) The brute force way is to figure out whether your battery loses voltage rapidly. This is done as follows:
With the key off, fan off, AC switch off, radio switch off, hood unlatched, you outside the vehicle and the doors shut and locked, wait 1 minute for your various computers to calm down and shut off. Measure your voltage. (Write it down if you are like me.) Walk away for two hours, leaving your vehicle undisturbed (do not trigger your door locks). Measure your voltage again. It should read the same. If it has declined only 1/10 of a volt it is possibly incidental. But any more than that and you have a parasitic drain. Something drained that battery down. In my case, I lost 0.3 volts.

(2) The shade tree way is to use a multimeter set on DC mili-amps and take off your negative cable and measure for current flow. How to do this handsfree? With the negative terminal of the battery disconnected, clamp one lead of your multimeter to the negative terminal (VERY gently with clamping pliers), and jam the other lead into the crack of the negative cable clamp. On my vehicle, I get .8 amps (if I am reading it right!) for twenty seconds, and then it declines and stays at .6 amps. Translation--a computer draws power for twenty seconds and then shuts down. After that I have a large problem still. OR more than one problem...

(3) The smart guy way--use milivoltage measured across fuses. There are youtube videos out there for this--I will not try to explain it here.

It all adds up, so you may have more than one problem to deal with. An old car has lots of old things in it, and all parasitic drains add up. The total of all of the parasitic drains is what is draining your battery, not necessarily just one parasitic drain. To start with, your vehicle always is draining from five sources by design: First, the battery just slowly drains itself. Leave a battery for a year on the shelf and it will have drained some. Second, your vehicle at some point in its life probably had a key fob, so is still listening for your radio signal to unlock the doors. That costs something. Third, it holds the settings on the engine and transmission computers for the learning it does while operating the vehicle. Fourth, the radio has presets that are maintained by the battery's current. And fifth, it has a number of computers that use some current until they go to sleep, usually within a few seconds of the key being off. Finally, as a sixth source of drain, there are lights which could still be on--headlights and dome lights. All of these are by design, and any of them that generate larger than normal drains could be adding to the mix. And there are a few more, like your brake lights and starters which have a switch on them that could be a source of drain.

Check the usual suspects first: From reading on the internet, I have a list of usual suspects, in declining order. Your problem could be something really odd, but it pays to check these first, since other people report problems with them:

(1) Let's start with eliminating the stupidly obvious first--maybe something is still on. Check your dome lights and door-triggered interior lights. They should be going out. Walk around and check your headlights and tail lights. Check your dash to see your open door warning lights are going on and off as you open and close your doors. You don't want to go overboard in checking wiring or anything like that yet--just look and be sure you aren't missing a lit bulb somewhere.

(2) An aftermarket radio or head unit or other after-market sound equipment. Even when they are properly installed, they can go bad and place a high continuous load on your system. Keep in mind they have a power feed from the battery to keep their programming. How to check? First, clamp your driver door open switch closed. Wait a minute for computers to shut down. Then pull your radio fuse and measure the drain. If it went away, it is probably one of your problems. This assumes you did not steal power from another circuit when you installed the radio... You can always disconnect the equipment itself to check it--often this is more definitive. This falls under the heading of "You are often your own worst enemy", or "This is why we can't have nice things..." 'Nuff said there.

(3) An alternator that doesn't handle its very huge connection to the battery well. An alternator, when running, has a huge amount of power feeding from the alternator to the battery. And when it is off, it has a continuous power feed back from the battery, for a swing of over 25 volts and as much as 160 amps. It has to handle that swing internally. Alternators have a way of losing that ability, especially on Monteros when they get oil dripped into them. How to check? With everything off and your meter set up (see above), confirm you have a draw again. Then unhook the main alternator terminal by removing the air filter box and removing the 12mm nut from the large cable going to the back of the alternator. A red soft plastic cover will need to be peeled back to do this. Move the cable away from the alternator, but do not let it touch anything else because it has the full power of the battery positive side running in it and will short if it touches anything else. Wrap it in a cloth if necessary. Measure your draw. If it went down or disappeared, replace your alternator (or the electronics of it, since it is not likely to be the alternator windings that do this, but the regulator electronics). Repeat your test to be sure by reattaching the terminal, reading the draw, and removing it again and reading the draw.

What if you haven't found all of the parasitic drains yet:

Check your fuses to isolate your problem: If you haven't found the draw yet, begin removing fuses one by one, checking your multimeter, and replacing them. Sometimes you will wake up a computer by doing this, and have to wait for it to go back to sleep, so be prepared to wait a few seconds if something wakes up. You should do this twice, with the key off. Why twice? Because you are likely to miss something the first time, and you can get a false negative reading as well on just one pass. Start with the engine compartment fuse box next to the battery. Then proceed to the two fuses next to the fender. Then proceed to the fuse box located in the driver footwell, remembering to clamp the door switch closed. This is where the third "smart guy" method that measures micro-voltage across the fuse comes in handy.

Check your relays: Using the same method, check your relays. A relay often has a always live terminal, and it can have a carbon track or corrosion or a partial fusing of points that causes a drain. Remove one at a time, and put it back before removing the next one, reading the meter for a decline in draw.

Starter? I read one reference to someone (on a non-Mitsubishi) who had a parasitic drain from a starter solenoid with a carbon track on it. It is logically possible, but rare, I think. The starter solenoid on a Montero Sport is buried under the engine, and is hellish to remove. I would not begin here, and would approach it very carefully, given how difficult it is to replace.

Other things you should do:
(1) Clean your battery terminals and wipe off the top of the battery.
(2) Make sure your battery clears your hood. One guy said this caused his draw on his Montero.
(3) Clean all ground straps--there are two or three on your intake manifold, and ends on the body too, and the battery grounds to the body somewhere too. Anytime you see a ground strap, clean it, anywhere. It is just good practice.
(4) Clean the alternator main wire tab, and inspect the thick cable for corrosion at that end.
(5) Inspect the positive and negative battery clamps and vicinity for corrosion.
(6) Remove and clean the bolt and terminal by the 100 amp fuse in the engine fuse box.
(7) Deal with the oil dripping off of the engine onto your alternator. New valve cover gaskets, new front cam seals are a minimum. While you are there, change your plug wires and plugs, timing belt, water pump, front main seal, timing belt tensioner, idler pulley, etc. and clean and grease all three belt tensioners, and replace your intake manifold gaskets as well.
(8) Check your charging voltage. It should be about 14.5 volts with the engine running and most things off. Try it also with the A/C blasting, headlights on, and wipers on high, the radio on, the dome light on, a door open and both map reading lights on. I.e. with the system fully loaded down. It should stay above 12.4 volts, the voltage that continues to charge your battery, and your headlights should not have dimmed significantly. #1,3,5 and 6 above are critical to this being a healthy situation for your vehicle.

Last edited by jburney; 11-19-2018 at 11:14 AM. Reason: Added "Things you should be doing" #8.
Old 11-15-2018, 07:28 PM
Senior Member
Join Date: Oct 2004
Location: Washington State
Posts: 1,311

This is a good approach. There is a fourth way to do it. It's a variation on the second approach you describe:
Connect the multi-meter in mA mode in series between the negative battery post and negative battery cable (just like in the write up).
Close all doors, wait a minute. Note the current reading on the multi-meter. If the draw is high, start pulling fuses one by one. While doing this, watch the readings. If no change, plug the fuse back in and move to next one. If you have a significant drop in draw - you found a circuit which has parasitic draw. Then you can focus on what on that circuit is drawing excess power.
You need to do this with the fuse box under the hood and also with the one in the passenger compartment. To successfully work with the internal box, tape the door switch, so that the dome lights stay off while you have driver's door open.
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