Solving Automotive Electrical Problems
Parasitic Draw Testing
Say you leave your vehicle sit for long periods of time and the battery goes dead. You’ve either checked or replaced both the battery and alternator, and you know they’re good. So what’s going on? You might have a parasitic draw.
A parasitic draw is an excessive electrical load on the system that happens after the vehicle is turned off. There will be some activity and loads when you turn your vehicle off, your clock circuit for one. In many modern vehicles, when you shut down and remove the key, a series of events happens that can draw current for several minutes after you turn the engine off. This is normal. To see if this is excessive and test for a parasitic draw, you’ll need a DVOM (Digital Volt Ohm Meter) capable of testing amps.
Often, when doing this test, you need to move your test leads on the DVOM to a different location when testing for amps, so be sure to check for this. It’s also important to note that you need to make sure everything is off when doing your testing. Don’t leave the trunk or any doors open, and make sure the key is removed from the ignition. This way you’re sure that there won’t be any electrical loads that you induced when doing this test that would give you false readings.
To perform the test: Remove the negative battery cable. Some people remove the positive cable to do this test, and that’s fine, but I recommend the negative cable when doing parasitic draw testing. Put your meter on the highest DC amp scale. This might require that you move your test lead to a special location on your DVOM. Place the leads in series between the negative cable and the negative battery post and take your measurement. If you see a negative number, switch the leads.
To be honest, it doesn’t matter, because the readings will be the same. You don’t want to see a reading above 50 milliamps. I know I told you to start with the highest scale, which might be close to 10 amps. If you don’t see a reading when you’re on the highest scale, great. You want to do it this way because some amp draws can be pretty high, which could damage your meter if you’re on a lower scale. If you don’t have a reading on the high scale, switch to the lower scale. Don’t forget to switch the leads if you need to. Once again, you’re looking for less than 50 milliamps. If you see a reading above 50 milliamps, your draw is excessive and it can drain the battery. The higher the reading, the faster the drain.
A couple of things to note: Some modern vehicles, especially luxury vehicles, have systems that remain on after the key has been removed and the doors have been closed. These systems might remain on for up to 30 minutes after shutdown. Keep this in mind when doing your testing. You might have to wait with your meter still hooked up for 30 minutes or more to get an accurate reading. Once you unhook the meter, things start all over again.
So you’ve done the test, you’ve waited an appropriate amount of time, and you’re still seeing above 50 milliamps. The next step is to start removing fuses one by one while observing the amp readings. If you see a sudden drop when removing a particular fuse, this is likely your culprit.
The next step after you find the offending fuse is to find a wiring diagram showing what’s on that circuit. After that, it’s a process of further elimination. Unplug each component in that fuse’s circuit till the draw goes away. For example, if the fuse controls the radio and power antenna, plug the fuse back in and unplug the antenna. If the draw goes away, you’ve narrowed it down to the power antenna. If it doesn’t go away, unplug the radio and recheck your reading. You’re probably getting the picture now. Here’s a video about parasitic draw testing you might find helpful.
Closing
I’ve done my best to cover the basics here. I’m hoping it’s enough to get you started diagnosing your electrical issue. There really is so much more, so if you’re interested in learning more, pick up some books or watch some videos on the topic to extend your knowledge of automotive electricity. BTW, the highest-paid technicians are the ones who do electrical and performance diagnosis. I hope to add more videos on this topic to my lineup as time permits. For now, check out these videos, which demonstrate some of the testing and principals mentioned above. Good luck.
Helpful Videos
I hope this information was useful to you. If you didn’t find what you were looking for, type in a few key words into the search at the bottom of the page. You can even type in specific check engine light codes. In addition to the code meaning you may find articles and forum posts that pertain to that code. If nothing comes up for your issue, sign up for our forum and ask your question there. We’ll be happy to help if we can. It’s free, all you need is a valid email address. Just be sure to respond to the conformation email to complete your registration. If you don’t see the conformation email, check your spam or bulk folder, it might have gotten stuck there.
Stay Dirty
ETCG
Written By EricTheCarGuy
Edited By Julie Hucke
20 thoughts on “Solving Automotive Electrical Problems”
Hans Veen
January 12, 2024 at 6:15 pm
mein honda civic 1999, EK/EJ nach Zylinderkopfdichtung weches wolle nicht starten.alle kontrol lampen brennen. verteiler ausgebaut Zündspule + modul gewechselt. läuft. habe motor abgestellt, wegen akühlwarren war noch nicht im motor, dann wollte er nie mehr starten 3 wochen suchen. verbindung vom Zündschloss zum Verteiler, kommt kein strom an. nicht zu finden. suche schaltplah. eventuel ein versteckter relaey. sicherheits schalter gefunden. perfekt. brauche dringens einen rat. Hans Ibiza Spain
Dan Kafun
June 2, 2023 at 4:03 pm
Eric… having an issue with my 2004 Element.. electric windows sporadically won’t work..I believe it has to do with the wire loom in the driver side door.. Do you have any videos on how to work/ troubleshoot the wire loom where it goes through the rubber conduit from the door to the Door frame..??
Thanks
Dan
Paul
January 10, 2023 at 10:58 am
Good morning. Im a ASE cert mechanic that was givin a 1994 honda accord ex 4 cyl. i put a quick used engine. I thought it would be a good idea to let my daughter use it as a car to learn how to drive in. I drove it for 2 months as a back up car and all of the sudden……. crank, no start. THIS IS WHAT I NOTICED. I turn the key to the on position…….. no fuel pump prime noise, check engine on, and d4 will flash. ALL INTERMITTINLY, you could sit and wait……. and sometimes click, all the sudden check engine light goes out, fuel pump primes and runs like nothing ever happen. MY QUESTION IS. is there a wiring diagram you may have or can get for me to start checking for powers, grounds and ignition voltages for the computer, ignition/fuel pump relay, ignition switch. Sorry to bother you. Im the kind of guy that wants to keep old cars going. Thank you in advance. Asking from Modesto, Ca
Vince
July 11, 2022 at 9:39 pm
Hi Eric just watched a video of yours for the Odyssey, I have 2006 Odyssey I put a new alternator , it’s not charging, wish you were near me you are the person I would trust. I changed alternator fuse 70/120 checked all fuses with voltmeter on ohms,. I really can’t figure this out , paid extra money for new , Remy , called Remy customer service state it’s possible the regulator inside alternator is defective. I’m not a mechanic, diy took me 3 hrs to do this,I definitely installed correct.it starts then battery is drained as I check w volt meter. If you have time can you please let me know what it could be so a least I can go from there thanks
Phil B
May 3, 2022 at 2:52 pm
my problem, 2015 elantra, the left turn signal lites , when turned on , blink at twice the rate as the right ones , left is abnormal condition, now if left turn signal on , and headlights turned on , the left turn lites both go off. any help here ???
Steven Ortiz
October 22, 2021 at 2:45 am
Tail lights on when battery gets connected
Felix Gonzalez
September 24, 2021 at 3:07 pm
I have a 08 accord and it has the vsa abs and brake light on and the dtc code DTC 121-11 I would like to know what to do because I have herd of a system update I called the honda dealer where I live and they don’t know what to do
Peter B
November 8, 2022 at 1:30 am
I have a 2013 CRV and a very similar problem. The VSA light comes on when in reverse and doing a turn. The code that comes up is 111-11 and here also the local Honda dealer does not know what to do.
george rodriguez
April 19, 2021 at 6:48 am
inhave a ford 2005 superduty 6.0 the 10 milli wire that goes on the positived side sparks
Randy
February 15, 2021 at 12:52 am
I have a 2010 dodge charge
When it’s in cruise control it starts to shuts off after a while the engine willt shut off.
The
Ross Melvin
October 28, 2022 at 10:43 am
HELLO…MY 30 FT. MOTORHOME HAS TOTALLY SHUT DOWN ELECTRICALLY. TURN ONTHE IGNITION AND NOTHING.. Was working fine till I parked it to winterize it..2 weeks later turned the key and nothing.Im wondering if it has lost it’s Ground….the vehicle is a 1997-98 GM Majestic Flyer ..
Remi
February 11, 2021 at 3:12 pm
Hey I have a problem I have a Honda Civic coupe 2005 I have change the speed sensors que the meter will go crazy and it shift hard a want to know what it could be because I already change the speed sensors
Shane Doxtator
February 11, 2021 at 2:52 pm
I have a 2007 Chevy Impala and i believe the issues i am having are stemmed from one. I was told it was a ignition problem don’t lock doors or it goes into security mode and you have to unplug battery until it resets. After i have drove it for a couple days i have realized that when the car isnt reading what gear it is in all the cluster gauges shut off and the doors start locking and unlocking, if i shut car off without seeing what gear it is in it goes into security mode. I also noticed whenthe cluster gauge goes out there is a noise by the fuse panel inside car
Areg
October 19, 2020 at 11:38 am
I have an 2012 civic ex. I have only 1 working key and want to buy 1 more and program it to the car… My question is what is the proper part number for my car key and how to program it to my car?
JERRY T.
August 15, 2020 at 12:39 am
I got this 2008 Chevrolet Aveo 5 4 door, can’t seem to find the power door lock relay for it the locks will trigger without hitting the key pad on my keys for it & it has drained batteries mis- firing. checked on all data but either I misnamed it or something
Nolan Ancel
August 12, 2020 at 2:57 pm
I have a problem with my 2009 Mitsubishi lancer SE… I am starting to lose hope. I did a parasitic draw test and took out 2 fuses that were pulling .84A. Now my car draws .07A or around 70mA. But my battery still dies… I don’t know what to do… I really love this car but for now it isn’t really reliable…
Scott
October 5, 2020 at 7:18 pm
Eric: finally a mechanic who understands cars.
Question: got a 2005 Chevy Express 3500, 6.0l, 4L80tranny.
Problem: when idling, vehicle shakes, kinda like a misfire. Their is no code.
I had a new engine installed, but new engine does same as old engine.
No mechanic has been able to guide me to a fix.
Any thoughts? 864-325-9939.
Juan Pendon
May 29, 2020 at 1:15 am
I got a problem on my dodge caliber 2008 sxt. Horn not working. I can’t find the horn relay. Need your help.
Jonathan Vasquez
May 9, 2020 at 7:51 am
Hi Eric, thank you for helping people like me fixing my own car. Have a question? My 1st and 2nd ignition coil is misfiring. They are both new with new spark plug. So i’m guessing the wire is broken is maybe the Computer module is messed up. Any tips or advice what to look for and how to fix it. Appreciate and thank you so much.
Ken Kastelic
May 1, 2020 at 2:51 am
Hi Eric, Love your videos. I have an Acura Tl type S 2007 (92k mls) and love the car. Its just i gave it to my wife and it just not her type of car. Maybe a little too sporty for her. I just watched you video on replacing the timing belt and water pump before i sell it. My problem is that i do have aftermarket wheels on it and the “TPMS” light is always popping up. How do i fix that issue? I bought new sensors and had someone install them but it still is happening. I want to sell it, but I want it to be a great car for the next buyer. Thank you so much for what you do. It is really appreciated.