How to test for parasitic draw with a Digital Multi Meter (DMM) capable of reading amperage. NOTE. PDF file included - available to download.

Test For Parasitic Draw
Digital Multi Meter (DMM) capable of reading amperage

1. Fully charged ~12.6V battery
2. Nothing ON in vehicle
a. Key out of IGN
b. Dome Light Off
c. Under Hood Light Off/Trunk Light Off
d. Radio OFF
e. Wait for any accessory devices (e.g. memory, ECM/PCM to stop)
f. Ensure peculiar buttons/switches are not turned on
3. Employing DMM, set to highest AMP scale
4. Remove negative (-) battery terminal cable from negative (-) battery post (anode)
5. Put one DMM lead on negative (-) battery lead terminal cable
6. Put other DMM lead on negative (-) battery post (anode) – READ AMPERAGE DRAW

DO NOT DETACH or TOUCH THE POSITIVE BATTERY TERMINAL CABLE

NOTE: The most you should see is ~50mA (milliamp). Anything >50mA signifies a significant AMP draw

Finding the circuit which contains the device creating significant amperage draw.

1. Permanently attach DMM terminal leads to items (5) & (6) above to continuously monitor/read amperage draw.

NOTE: If the DMM is connected, turn it OFF if you have to open the door, then reconnect the DMM after clamping/taping/closing the door – it could overload the DMM. When removing fuses, you MUST not have ANY devices ON. Therefore, and to that end, clamp/tape the door jam switch so the IGN buzzer is OFF and the dome light is OFF.

2. Begin removing fuses from fuse panel/box one at a time noting the amperage draw every time a fuse is removed. Continue to remove fuses one at a time until the total amperage draw is <50mA. Whichever fuse was removed which reduced the amperage draw to <50mA demonstrates the circuit which contains the parasitic draw.

Want to follow an instructional video?

 

Excellent video..learned simple way to at least find the circuit

 

Yet another example of internet/Youtube rangers exchanging bad advice for 5 minutes of fame. Using a DVOM as instructed above can turn into a $30-$60 mistake (price of replacement internal DVOM fuse) if the current draw exceeds 10 amps. A professional auto electrician would use an inductive amp clamp to safely determine the actual current draw value before shunting an amp meter between battery posts and cable terminals.

 

I prefer using a test light in place of a meter, bulbs are cheap and easier to see when you're by yourself.

 

Then....that is "your" recommendation. Drop the innuendos of others attempting to assist others. It is NOT bad advice. Is it necessary for you to display such a condescending attitude which speaks more towards flaunting and touting your horn than it does to provide assistance to others. Know-it-alls are a dime a dozen.

 

Agree. Yet I wrote it to assist those who might want to troubleshoot w/ a DMM, but your point is well taken.

 

Know it alls are a dime a dozen and take to the internet to prove it. I'm glad you see my point. People who are trained, skilled, experienced, made a good living in the field of the subject matter and attempt to provide correct advice are worth much more. Then there are those who take offense when they are called out for the BS spreaders that they are...
Here is another example of your how "your" procedure IS bad advice. Step e you state to wait for the vehicles memory to power down. Then in steps 4 through 6 you want to disconnect the - battery terminals and connect the DVOM. This will cause the vehicles control modules to wake up all over again. At this point are you reading a parasitic draw or normal vehicle operation?
Now, am I a condensing know it all or someone who just knows?

 

Not all DMMs open up the shunt (current sense) resistor when turned OFF, so damage from over-currents could still occur. It is best to connect the DMM across a shunt switch, and close the switch when you expect currents in excess of the DMM's rating to flow, open the switch to make measurements. One could argue to just use a DMM rated for the max expected current, however there's a good chance that a DMM rated for 50A (for example) may have trouble resolving (displaying) 50mA accurately.

 

Your post brings up some great points about using a DVOM for tracing parasitic draw. Kudos to you for sharing. Your comment about higher AMP scales reminds me about the first time I needed to use my shops inductive AMP meter function. It had two AMP scales, 700 AMP and 70 AMP. I thought how could this be helpful when I am testing for less then 1 AMP. Being unwilling to use my own DVOM (because of the unknown amperage draw) I had nothing to use lose by trying the 70 AMP scale. I found it measured milli amps with dead on accuracy. Who knew?
Reviewing the quote you included from the OP it seems like a step may have been left out.
NOTE: If the DMM is connected, turn it OFF if you have to open the door, then reconnect the DMM after clamping/taping/closing the door – it could overload the DMM.
The OP instructs us to "to turn off the DMM". Then states to "reconnect the DMM"
This may confuse some of those who are trying this procedure for the first time. Perhaps it should have read "disconnect the DMM if the door has to be opened, then reconnect after the door is closed". (My quotes) It may also should have included to wait for the modules to power down. On newer vehicles the power down time (AKA going to sleep) may take upwards of 30-60 minutes.

 

Valid point. There is some responsibility of ownership when someone purchases/owns a product. There exist a wide variety of DMMs & it is for this reason the write-up states:

If someone owns and knows how to operate a DMM (they read the directions) and they know the difference between DC & AC, the write-up remains, IMO, a decent process to detect a parasitic draw. Perhaps the write-up should state you need to set the DMM to DC, where the black lead is attached to the DMM, where the red lead is attached to the DMM, how to turn it OFF/ON. I didn't think it necessary to discuss the difference between AC & DC - perhaps a discussion regarding AC & DC, &/or the COM port &/or ohms, resistance, voltage & the like are necessary? I was attempting to keep it simple.

 

The video expressly states in several areas to allow the vehicle to completely go to sleep so any "keep alive" devices have fully gone to sleep prior to making any readings. I thought (hoped?) it would be apparent to someone who owns/uses a DMM the several statements in the write-up:

...maybe it's not apparent enough? I was really attempting to keep it as simple as possible. Perhaps that failed?

 

This was so helpful to me, great video and information, my battery would go dead in 1 day, and found I had a draw on battery, radio OEM amplifier was the culprit after testing as described, replaced radio amplifier and problem solved. I also found my sunroof drain was not connected and was dripping water on the warm amplifier when radio used, took amplifier apart and found green corrosion on circuit board inside the unit.

Bob

 

Bob, you dodged a bullet on that corrosion as it doesn't look terrible but could definitely be a source of current drain. I have seen a lot worse in my day. Dynoking, I can understand your frustration with attention seeking web posters as they are no doubt out there. I don't know that guy in the video or of him so can't judge. For what it's worth, the inductive amp meter isn't something I am too familiar with, I don't have one in my tool box and never used one in 21 years of Navy avionics repair work. Back then we understood them to be used for extremely high current measurement applications so we always used DVOM/DMM for measuring current. We of course used safe procedures as you and Norm have already discussed. I really don't see much error in Norm's procedure and would probably do the same to find parasitic draw. Finally your DVOM must be really high dollar to take a $30-$60 dollar fuse, my Fluke uses a standard fuse that costs a couple bucks.

correction on my last statement, closer to $20 bucks, I apologize.

 

Yeah, those high current, 1000 Volt fuses are not cheap.

https://www.digikey.com/en/products/...wAMAzCwJzd6DIA