Multimeter Values for testing Parasitic Draw - Page 1
Forum section: electronics / beginners

author: CoriolisEffect
author_rank: Newbie
timestamp: September 26, 2025, 02:08:58 pm
content: Hello,I was testing the parasitic draw on my Jeep Gladiator, and I was using the method of disconnecting the negative terminal from the battery and attaching one probe of the multimeter to the Negative battery terminal, and the other probe to the negative cable going to the Jeep.I have 2 Questions:1) I am trying to Understand the value I get, And I'm not sure if I'm meeting my decimal points right? I tried it two ways. One set 10A and and one set to mA (pictures attached). For the the mA reading is it literally 1.16mA, and for 10A it's 0.18 Amps? If a car should be under 50 mA, then my values are very well so I'm good? Unless I'm reading it wrong?2) When doing the parasitic draw test, it is advised you need to let your car go back to sleep, and to let it sit for up to an hour. It is also advised not to open any doors or turn anything on as it will wake the car up and cause extra current draw. That's what I did before I did the test. I wanted to test waking my car up to see if I get any extra draw. But when I have the multimeter hooked up and the negative disconnected from the battery, I get absolutely no power. I'm not even able to turn the light on. So my question is why doesn't the car wake up, like others have stated that this will happen? Am I doing something wrong?Thank you in advance and I hope this post makes some sense LOL!

author: jwet
author_rank: Frequent Contributor
timestamp: September 26, 2025, 03:11:32 pm
content: Remember how your DMM measures current. It uses a shunt and measures voltage across it. On the 10 amp scale, the shunt R is .01 ohm so a 10 amp load gives you 100 mV. On a 1 ma scale, the shunt might be 100 ohms. The basic meter sensitivity is about 100 or 200 mV full scale. Dave's Microcurrent gadget uses a nice amplifier and can reduce the burden voltage by 100x (it take a nice chopper amp to do this). Disconnecting the battery to insert your meter is pretty disruptive in modern cars, they take a while to settle down and go to sleep after a full power loss. Some things like the audio head unit have to be reinitialized, etc (anti theft). Use a high resolution and a reasonable range on your meter- perhaps a 1 amp range or even 10 amp range. If your meter has 4 or more digits, you can resolve 10's of mA still. Don't turn the ignition to on or start! Though the average currents are extremely low, there are often medium current spikes (Key fob receiver polling for example or a solenoid valve gas tank vent) that can draw real currents. Some cars have known parasitic issues or failure modes. The keyless entry module on most 2010 ish Hondas could get stuck on and draw about 100 mA continuous- this will kill a battery in a week or less. Traced to bad caps in the ECU. Good luck. Anything less than 10 mA isn't bad, 1 mA is great.

author: floobydust
author_rank: Super Contributor
timestamp: September 26, 2025, 04:58:16 pm
content: Welcome to the forums2) you have the multimeter in mA mode but are using the (wrong) 10A jack - so it will read silly low. Don't use that number.I would stay in 10A jack+mode.For your test it is reading 0.188A or 188mA which is high and means something is running, has not yet gone to sleep.When cars are sitting there, key off - the ECU does do some housekeeping.They will do a canister purge test cycle (vac pump near the fuel tank making noise).If it's hot weather, cycle the fuel pump to cool off the throttle body and injectors, prevent fuel percolation.Complicated is interdependent computers can get stuck on, one waiting for another module to finish and go to sleep etc. Ford is not doing so great with firmware dependencies with Infotainment, BCM etc.The BCM is always on, remote control RX running listening for keyfob RF etc.Subaru had big problems with high parasite draw- leading to class action lawsuit. The limit is around 75mA but they have 125-150mA which caused short battery life, dead batteries etc.ECU Firmware fix helped a bit but not really. Don't leave them parked for long lol.

author: ledtester
author_rank: Super Contributor
timestamp: September 26, 2025, 05:16:52 pm
content: To measure current one lead should be in the COM socket and the other should be in the 10A or uA/mA socket depending on which dial setting you are using.Attached is a better pic of the MM720 meter.

author: mikerj
author_rank: Super Contributor
timestamp: September 26, 2025, 08:56:56 pm
content: Your method is very likely to blow the multimeter fuse, at least on the low current ranges, as there is a significant current draw when you connect the battery and all the modules wake up. You need to have the DMM bypassed when connecting the ground cable and during the 10-15 minutes it can take for all modules to enter sleep state.One way to do this is to have the negative clamp connected not not tightened, wait 10-15 minutes with all doors closed to ensure all modules are sleeping, then with the DMM in current range place one probe on the lead battery terminal, the other on the battery terminal clamp and then carefully pull the battery clamp off. As long as you maintain continuity nothing will wake up and you'll get the correct sleep current.

author: CoriolisEffect
author_rank: Newbie
timestamp: September 26, 2025, 10:30:22 pm
content: Thank you for the info!

author: CoriolisEffect
author_rank: Newbie
timestamp: September 26, 2025, 10:36:48 pm
content: Ok, Thanks. So Using 10A, 0.188 = 188mA. And normal would be anything around less then 75 to 50mA. I wonder why the jeep doesn't wake up when I try to turn a light on (with the multimeter hooked inline) only wakes up when I hook the battery back up. Maybe I'm doing the procedure wrong?

author: CoriolisEffect
author_rank: Newbie
timestamp: September 26, 2025, 10:40:44 pm
content: Now I only have the DMM hooked up when the NEGATIVE terminal is disconnected from the battery, then I hook up the DMM inline on the NEGATIVE side. Do you mean l, this could blow the DMM fuse?

author: CoriolisEffect
author_rank: Newbie
timestamp: September 26, 2025, 10:43:34 pm
content: I just realized I didn't quote any of you to my responses. But al least I I learned the term DMM lol!

author: Stray Electron
author_rank: Super Contributor
timestamp: September 26, 2025, 10:54:50 pm
content: I test my vehicles the same way but as Jwet points out, disconnecting the battery is very disruptive to the electrical system of a modern car. Now what I do is to loosen the - battery clamp and attach one lead to the clamp and then poke the other lead unto the center of the lead battery post of the - terminal and hold it there and then pull the clamp off of the post. You can pull the clamp up around the probe if necessary. That will instantly give me a reading. But you need to know something about what current to expect and have your meter set appropriately beforehand. After I get the reading I push the clamp back onto the terminal and then remove the test leads and then retighten the clamp. Doing it that way I don't lose any radio, clock or computer settings and it doesn't even wake up the electrical system.As others have pointed out DO NOT open a door or do anything to wake up the electrical system during the test or the current could sky rocket and damage your meter. If necessary perform the test with the meter on a higher range and get a reading, then reconnect the battery clamp and then change your scale and then repeat the test.And BTW I don't use one of my GOOD meters for this. I use an old Harbor Freight meter that I got for free. It's more than accurate enough and if I damage it then I'll just get another. it's not like damaging $800 HP or Fluke meter.I've found current draw testing VERY effective for finding electrical problems. You can have someone pull fuses while you hold the probes in place and you can quickly find what circuit has excessive power draw.

author: Stray Electron
author_rank: Super Contributor
timestamp: September 26, 2025, 11:11:56 pm
content: "But when I have the multimeter hooked up and the negative disconnected from the battery, I get absolutely no power. I'm not even able to turn the light on."That's probably because your meter is set for less current than what you Jeep draws when it wakes up. If your meter is set for 100 ma range then that's pretty much going to be the limit of what you can draw. After that the meter is going to have so much voltage drop that the voltage in the electrical system will be almost zero. You probably need to be on at least a 10 Amp range when your Jeep wakes up and even that may not be enough. Modern cars so all sorts of testing, pre-pressurizing fuel lines, purging vacuum systems, preheating O2 sensors (four of them!), testing various sensor, etc, etc when you first turn them on. Possibly even adjusting the seats and the mirrors!Your lights will certainly require more than 100Ma and very likely more than 10 Amps! Seriously, I would set a meter for 50 amps and then try turning on the lights and see what they draw. While you're at it, let your Jeep go to sleep and see roughly what the current draw is and then open a door and wake it up and see what it is. Also trying rolling down a window. Or just turn the ignition on but don't start the engine. All of that should give you a good idea of how much current each operation takes.

author: ledtester
author_rank: Super Contributor
timestamp: September 27, 2025, 12:48:14 am
content: Consider getting a clamp meter which can measure DC current. Then you won't have to break any connections and it won't interfere with starting the car.The Uni-T UT210E is a decent choice. I'd say it's accurate to +/-5mA or so. There's also been a lot of discussion on this forum about it.Note that most clamp meters only measure AC current - so make sure the one you get also does DC current.

author: Aldo22
author_rank: Super Contributor
timestamp: September 27, 2025, 07:11:41 am
content: Yes, a clamp meter is much more suitable.I would recommend an OWON CM2100b with Bluetooth. This allows you to read the measurements on your smartphone, even when you're sitting in the car.https://play.google.com/store/apps/details?id=com.owon.imeter&hl=gsw

author: mikerj
author_rank: Super Contributor
timestamp: September 27, 2025, 11:41:02 am
content: Quote from: CoriolisEffect on September 26, 2025, 10:40:44 pmI only just saw the pics in your OP, one of your photos shows the test lead in the 10A socket on your DMM and the range switched to mA which is not a valid setup so anything displayed is meaningless. The mA range only works correctly when you have the test lead plugged into the mA/uA socket on the meter.Regarding blowing fuses, the problem is that when the battery is first connected after being disconnected there will be a significant current current flow for a short period, this is why you typically see/hear a spark when connecting the ground clamp onto the battery. This would definitely blow the 800mA fuse on the mA range, the fuse on the 10A range may survive but I wouldn't guarantee it. This is why you need to connect the battery without the multimeter in circuit so this transient surge current stabilises, and then find a way to get the meter in circuit without breaking the circuit as I described.

author: CoriolisEffect
author_rank: Newbie
timestamp: September 27, 2025, 03:10:13 pm
content: Quote from: mikerj on September 26, 2025, 08:56:56 pmOk I have to try this method, thank you for helping me learn.

author: CoriolisEffect
author_rank: Newbie
timestamp: October 02, 2025, 10:44:00 am
content: Quote from: Aldo22 on September 27, 2025, 07:11:41 amI ended up getting this clamp meter. It's great, It seems like a much better way to measure for parasitic draw.Thanks for the advice. I've learned a lot form this forum already. Unfortunately, I've gone down a rabbit hole and I ended up ordering the EEVBlog BM2257 lol.So with the clamp meter I ended up with a parasitic draw of about 50 to 60 mA. This is after letting the car sleep overnight with everything "latched". So that seems a little too high.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: October 02, 2025, 01:37:46 pm
content: Good Morning CoriolisEffect, 50 mA draw is not considered excessive draw, because of the circuits thatneed to be on when the vehicle is off, like the alarm system. My 2008 Honda Ridgeline draws53 mA at rest. I believe it varies, depending on the vehicle, but should never exceed 80 mA.

author: CoriolisEffect
author_rank: Newbie
timestamp: October 03, 2025, 06:11:37 pm
content: Quote from: BILLPOD on October 02, 2025, 01:37:46 pmOkay, thank you for the information. I'm trying to figure out what's causing my check engine light for charge system. Before it was because of the auxiliary battery setup and I had both batteries replaced.Alternator checked out fine. (Well at least from AutoZone and the dealership). Maybe my IBS sensor is bad.Let me ask you all this. I trickle charge my car battery overnight. Before I left for work I checked the charge showed full @13.11 volts. I then drove 15 mi to work about 25 minutes , and then 15 mi back home, about 30 minutes. I just checked the battery and it's showing 12.85 volts. Is this normal for the voltage to drop like that? Or should the alternator have charged it? Is is it because it wasn't enough drive time to keep the charge up?