I fixed a parasitic drain on my car in 408 days(davidmuller.github.io)
davidmuller.github.io
I fixed a parasitic drain on my car in 408 days
https://davidmuller.github.io/posts/2023/04/10/how-i-fixed-a-parasitic-drain-in-408-days.html
503 comments
Well this is timely. I have a parasitic draw on my NC Miata. The first mechanic just replaced the battery. The second told me it's normal for the battery to die if you don't drive it for 3 days (because "cars have computers now"). It seems like mechanics really don't like digging into the electrical part of the car... but these days that encompasses more and more of what can go wrong.
Without time to dig into it myself I've just been parking it with a battery tender every time I come home.
Without time to dig into it myself I've just been parking it with a battery tender every time I come home.
My father (a professional auto mechanic) took about 6 months to find a random engine shutoff during harder cornering in his Toyota, the culprit was a damaged inner insulation layer for a few wires within the wrapped wiring harness for the ECU, engine moving on the engine mounts would sometimes cause a slight harness shift and a short would cause a hard reset of the ECU.
Another story I have is my computer geek friend finding an issue with my Subaru Legacy, when no other mechanic could (I tried 3). The issue was that the car was old, first gen OBD, he downloaded some legacy asm ECU reader and made a diagnostic cable from spare parts, the issue was that the car would not start when cold, or be extremely hard to start. The culprit was damaged wire that tells the ECU that the engine is in cranking condition, therefore needs a different fuelling mode, without seeing this mode there was not enough fuel to start when cranking. Eventually this was found by hooking up an oscillograph to see the injector impulse length (duty cycle), as the old gen. diagnostic didn't show any errors, he compared a working car injectors to mine when cranking cold and found this. 10 years later I'm still amazed by his skill and dedication, I'd have scrapped the car otherwise. The car was sold eventually to another person who restored it (rust repair mostly) and his wife still drives it to this day, a 1994 Subaru Legacy.
Another story I have is my computer geek friend finding an issue with my Subaru Legacy, when no other mechanic could (I tried 3). The issue was that the car was old, first gen OBD, he downloaded some legacy asm ECU reader and made a diagnostic cable from spare parts, the issue was that the car would not start when cold, or be extremely hard to start. The culprit was damaged wire that tells the ECU that the engine is in cranking condition, therefore needs a different fuelling mode, without seeing this mode there was not enough fuel to start when cranking. Eventually this was found by hooking up an oscillograph to see the injector impulse length (duty cycle), as the old gen. diagnostic didn't show any errors, he compared a working car injectors to mine when cranking cold and found this. 10 years later I'm still amazed by his skill and dedication, I'd have scrapped the car otherwise. The car was sold eventually to another person who restored it (rust repair mostly) and his wife still drives it to this day, a 1994 Subaru Legacy.
I used to be a computer engineer working on embedded systems for automobiles. Quiescent current is what the normal proper draw is called for these systems when the car is off. We worked very hard getting these numbers in spec but it was hard to catch everything especially in this case where the issue is probably due to software missing the sleep state for that module. This could be from bad code or your CAN/LIN bus is messed up in your car. 99% of mechanics (and engineers) have no idea where to start with debugging these issues and the answer will be "replace the module".
I have failed to find the parasitic draw on an RV (slower than this one, it takes a couple weeks to kill the battery). I finally got a "Top Post Battery Master Disconnect Switch", which is a little dinglebob that goes between the battery post and cable and lets you easily break the circuit. I highly recommend the $12 solution for an intermittently used vehicle.
This is type of thing I've seen Eric O. over at South Main Auto[1] fix in dozens of videos. Mad troubleshooting skills, works hard to find root causes of things. He's pretty amazing, hidden away in some no-account town in upstate NY.
1 - https://www.youtube.com/@SouthMainAuto
1 - https://www.youtube.com/@SouthMainAuto
Thanks for this timely post. I'm literally in the middle of running down a parasitic drain on my Nissan Xterra.
I tracked mine down using a different method which helps when your fuses don't all have test points (and no conversion table needed).
- Disconnect negative battery cable
- Switch your multimeter to 10A (don't forget to swap lead ports)
- Connect the multimeter in-line between the negative cable and negative battery post
- The readout on the multimeter should now tell you how much drain you have
- Start pulling fuses one by one until you see the amps drop to normal
I tracked mine down using a different method which helps when your fuses don't all have test points (and no conversion table needed).
- Disconnect negative battery cable
- Switch your multimeter to 10A (don't forget to swap lead ports)
- Connect the multimeter in-line between the negative cable and negative battery post
- The readout on the multimeter should now tell you how much drain you have
- Start pulling fuses one by one until you see the amps drop to normal
One thing I haven't seen mentioned yet: If your battery is dying way sooner than it should be, and if you have _any_ aftermarket equipment installed (radio, backup cam, alarm, remote start, trailer light module), that should always be the VERY first thing to suspect.
These things are not engineered to the same requirements as the OEM electronics, and if they are drawing 10s of milliamps while the car is off, that is certainly enough that you wouldn't notice an issue with a newer batter and a car being driven every day. But if your driving patterns change and the battery gets older, suddenly your battery is dying all the time and "nothing has changed."
These things are not engineered to the same requirements as the OEM electronics, and if they are drawing 10s of milliamps while the car is off, that is certainly enough that you wouldn't notice an issue with a newer batter and a car being driven every day. But if your driving patterns change and the battery gets older, suddenly your battery is dying all the time and "nothing has changed."
I found that my old (1997) Range Rover would flatten its battery after being parked outside my house over a weekend. If I didn't drive it for two or three days, it would be too flat to start.
It turns out that the BECM (body ECU) wakes up from sleep if it hears anything coming in from the RF keyfob receiver, on 433.92MHz, a standard ISM frequency. If it's not a valid fob code (and there is a surprisingly complex rolling code sequence) it'll go back to sleep after 20 minutes or so.
The oil tank gauge for my central heating had a remote sensor that... yup. Transmitted on 433.920MHz, of course.
The aerial for the keyfob is on the rear right corner of the vehicle, the oil tank for the heating was on the left-hand side of the driveway right at the back of the house, so when I backed into my driveway it was right beside the receiver.
I managed to do just fine with popping the lid off the oil tank once a month and looking inside to see how much fuel was left, having taken the battery out of the tank sender.
It turns out that the BECM (body ECU) wakes up from sleep if it hears anything coming in from the RF keyfob receiver, on 433.92MHz, a standard ISM frequency. If it's not a valid fob code (and there is a surprisingly complex rolling code sequence) it'll go back to sleep after 20 minutes or so.
The oil tank gauge for my central heating had a remote sensor that... yup. Transmitted on 433.920MHz, of course.
The aerial for the keyfob is on the rear right corner of the vehicle, the oil tank for the heating was on the left-hand side of the driveway right at the back of the house, so when I backed into my driveway it was right beside the receiver.
I managed to do just fine with popping the lid off the oil tank once a month and looking inside to see how much fuel was left, having taken the battery out of the tank sender.
Had the same problem recently with a 2011 Mercedes. Didn’t figure it out until eventually the Keyless Go module (which allows push to start and automatic door unlocking) died. This fixed the parasitic drain.
Apparently when these sorts of modules are dying they fail to turn off and drain the battery by constantly searching for the key fobs. Incidentally while the battery drain was going on the key fob batteries were dying extremely quickly as well, also suggesting a lot more communication than normal was occurring.
Apparently when these sorts of modules are dying they fail to turn off and drain the battery by constantly searching for the key fobs. Incidentally while the battery drain was going on the key fob batteries were dying extremely quickly as well, also suggesting a lot more communication than normal was occurring.
"Fixed" in the same way I can "fix" a stuck key on a keyboard by physically removing it. They've circumvented the problem but are left with less than what they originally had.
In the 00s, my dad had an issue with the infotainment system of its Peugeot 407 that would no longer boot.
An official Peugeot mechanic told him that it would cost something like 4200€ to replace the unit, so he asked me if I could have a look.
After a quick search, I found an update for his system, burn it on a CD, and put the CD into its car.
The system updated, and then would work normally. Problem fixed for one hour of my time and a CD.
An official Peugeot mechanic told him that it would cost something like 4200€ to replace the unit, so he asked me if I could have a look.
After a quick search, I found an update for his system, burn it on a CD, and put the CD into its car.
The system updated, and then would work normally. Problem fixed for one hour of my time and a CD.
Hah. I’ve replaced the battery in our Subaru Outback on average once per year, which is way too high for this environmental minded person.
I just went out last night to grab something from the car and it was making a loud electrical whirring noise. I had driven it several hours prior, no idea how long it had been going. I recorded a video and it is clearly audible. I started it and turned it off again, and the noise stopped.
Friend of mine (and several other commenters here) has an old pickup with a switch on the steering column that cuts the circuit at the battery, I’m ready to install one on both my cars.
I just went out last night to grab something from the car and it was making a loud electrical whirring noise. I had driven it several hours prior, no idea how long it had been going. I recorded a video and it is clearly audible. I started it and turned it off again, and the noise stopped.
Friend of mine (and several other commenters here) has an old pickup with a switch on the steering column that cuts the circuit at the battery, I’m ready to install one on both my cars.
South Main Auto has an excellent youtube channel with various parasitic draw videos. For those struggling, it's a good watch.
Here's one such: https://www.youtube.com/watch?v=qDqlG5bRq8k
Here's one such: https://www.youtube.com/watch?v=qDqlG5bRq8k
Anecdata: Some Hondas (e.g . 2010 Element) exert enough parasitic drain to put the car into a chronically undercharged state if a door is left ajar overnight.
The wrong thinking turned out to be: Car is safe in garage, interior lights go off, and my hands are full now -- why bother going back to the door to shut it completely?
The wrong thinking turned out to be: Car is safe in garage, interior lights go off, and my hands are full now -- why bother going back to the door to shut it completely?
Personal vehicles are getting way too complicated now. Too many electronic components that can be points of failure.
Recently viewed a video on “steer by wire yoke”
https://m.youtube.com/watch?v=agMrewRJTow
It’s very interesting but there are so many additional motors, sensors, and actuators to simulate the same experience as mechanical based steering.
If you lose electronic assistance in traditional mechanical based steering, you have to apply more force as a driver and makes the experience difficult.
What happens if I lose one or more components in this “steer by wire yoke”? Seems like as a driver you are shit out of luck. If you are a pedestrian, bye bye.
All I want is a walkable city with public and alternative forms of transportation. All of these “car innovations” are mostly useless.
Recently viewed a video on “steer by wire yoke”
https://m.youtube.com/watch?v=agMrewRJTow
It’s very interesting but there are so many additional motors, sensors, and actuators to simulate the same experience as mechanical based steering.
If you lose electronic assistance in traditional mechanical based steering, you have to apply more force as a driver and makes the experience difficult.
What happens if I lose one or more components in this “steer by wire yoke”? Seems like as a driver you are shit out of luck. If you are a pedestrian, bye bye.
All I want is a walkable city with public and alternative forms of transportation. All of these “car innovations” are mostly useless.
Had a similar issue with a 1.5-year-old vehicle that would have the battery fully drained in a little over a week if the vehicle wasn't driven. Had the dealership "fix" the problem three times and the problem was never fixed. I used the lemon law to get a brand new vehicle. I won't name the brand, but dealing with the manufacturer for this was rather trouble free.
Intermittent car issues are the worst! Related is the 'My car hates vanilla ice cream' story:
https://web.archive.org/web/20060213052358/http://www.campbe...
https://web.archive.org/web/20060213052358/http://www.campbe...
I've never understood why cars don't just cut power before the battery is too low to start. If that's too complicated then just have an option to cut all power after X hours of non-running time.
I bet the old popular theft of car radio is a root cause; cars needed to stay running to keep the alarm active and power the radio continuously so it wouldn't require the unlock code every time you start the vehicle.
It's actually pretty impressive how much power even a 200mA draw at 12V is over a few days; it's about 58 Watt-hours or 3.5 iPhone batteries per day.
I bet the old popular theft of car radio is a root cause; cars needed to stay running to keep the alarm active and power the radio continuously so it wouldn't require the unlock code every time you start the vehicle.
It's actually pretty impressive how much power even a 200mA draw at 12V is over a few days; it's about 58 Watt-hours or 3.5 iPhone batteries per day.
Not just for highly computerized cars, I have a 97 Ranger where literally everything is manual and I don't even have a dome light anymore. There's a parasitic drain I can't quite figure out so I just make sure to start it every once in a while. Since I'm a year round bike commuter the truck can sit around for a long time, especially in winter when there's no house and garden projects. I've considered adding a manual battery disconnect, the only thing I'd lose are the pre-programmed radio stations.
Electrical issues on cars are the absolute most maddening things to diagnose and fix. I’ve restored several cars and worked on every car I own and the one thing I loathe to do is figure out an electrical failure. Even in older cars, it’s a pain in the ass.
I have an 89 e30 and one time the dash cluster started acting up. Essentially the tach and speedo weren’t responding (they’re not cable driven). Took out the cluster, checked all the connections, checked the wiring diagram to see if there were any potential grounding points I might want to consider. Nothing.
Finally called a local bimmer indie shop and asked them what they thought and they directed me to the small reverse light switch wire that feeds down through the shifter hole into the transmission tunnel. Apparently it often rubs against the body and becomes shorted. I looked and sure enough it was bare. Patched it and all was well.
This wire, mind you, is not at all on the dash cluster circuit. There’s no reverse indicator light on the cluster or anything like that. I would have never had any reason to suspect it was the problem. This is the nature of automobile electrical issues.
I have an 89 e30 and one time the dash cluster started acting up. Essentially the tach and speedo weren’t responding (they’re not cable driven). Took out the cluster, checked all the connections, checked the wiring diagram to see if there were any potential grounding points I might want to consider. Nothing.
Finally called a local bimmer indie shop and asked them what they thought and they directed me to the small reverse light switch wire that feeds down through the shifter hole into the transmission tunnel. Apparently it often rubs against the body and becomes shorted. I looked and sure enough it was bare. Patched it and all was well.
This wire, mind you, is not at all on the dash cluster circuit. There’s no reverse indicator light on the cluster or anything like that. I would have never had any reason to suspect it was the problem. This is the nature of automobile electrical issues.
While not a fix for this problem, a nice form of insurance is a Lithium Ion jump start battery[1]. I'm amazed that a hand-held battery can discharge fast enough to jump start my car, but ... it works great.
[1] https://www.amazon.com/dp/B0B55RFM1Z
[1] https://www.amazon.com/dp/B0B55RFM1Z
My experience with car mechanics is they are good with mechanical systems, but have little understanding of anything electrical, and even worse with electronics.
P.S. If you're doing a bit of wiring on the car, don't use those crimp on wire connectors. They'll work ok for a year or so, and then start behaving erratically, slowly getting worse and worse. This is because the crimp is simply not tight enough, and the mating surfaces start to corrode.
The best solution is to strip the wire ends, slip some heatshrink tubing over the wires, cut the plastic off the butt crimpon connector, crimp it on, solder the wires to it, move the shrink tube back over the joint and shrink it on.
This goes for any crimpon connector.
Also, don't use the auto wire you get at your local auto parts store for anything in the engine compartment. It won't last in the heat. You gotta get heat resistant wiring.
P.S. If you're doing a bit of wiring on the car, don't use those crimp on wire connectors. They'll work ok for a year or so, and then start behaving erratically, slowly getting worse and worse. This is because the crimp is simply not tight enough, and the mating surfaces start to corrode.
The best solution is to strip the wire ends, slip some heatshrink tubing over the wires, cut the plastic off the butt crimpon connector, crimp it on, solder the wires to it, move the shrink tube back over the joint and shrink it on.
This goes for any crimpon connector.
Also, don't use the auto wire you get at your local auto parts store for anything in the engine compartment. It won't last in the heat. You gotta get heat resistant wiring.
> Since I don’t have Mazda’s proprieratry M-MDS diagnostic tool, I couldn’t disable the keyless module in software myself.
Ugh, imagine if normal computers were like that. "Since I don't have Intel's proprietary I-DBT diagnostic tool, I couldn't disable the wifi in software myself."
I guess we're half way there with phones.
Ugh, imagine if normal computers were like that. "Since I don't have Intel's proprietary I-DBT diagnostic tool, I couldn't disable the wifi in software myself."
I guess we're half way there with phones.
I had a 2005 Acura RL which had some pretty fancy electronics for its time. I gave it to my daughter a few years ago and she started reporting that the battery was dying. It would take several days to die, so at first she just jump start the car every couple of days. When she brought it home (she lives 5 hours away) I measured the current draw at >800mA when it should be <20mA.
These cars have a Bluetooth handsfree module that goes bad and starts leaking power. The fix is to bake them in the oven at 350F for 5min to reflow the solder. Already did this twice and then decided to just get rid of it. So that was not the problem.
She needed to get back so we figured out which fuse was the easiest to remove and she lived with that for a couple of months. In the mean time we figured out it was the MICU module, which is the module that controls all the electronic systems and security. Without this nothing works. I was told a new one would be north of $1200 and labor. If they could find one. The dealership said they would chase down the problem again for $165/hr just to be sure... And I would have to leave the car with them until they were ready. Possibly 3 weeks.
I found a couple of the units on ebay for <$100. One was from a 2008 and another one that had some broken plastic on the case for from an early 2005 (same as my car). I tried the first one, nothing worked, all kinds of systems failed. I learned there was an EEPROM chip in the Honda/Acura MICUs that store the codes to make the systems work and are unique for each vehicle. The Dealership can program them for a fee. Having a full electronics lab, I swapped the chips in no time. It was better, but the starter would not engage. In desperation, I did it again on the 2005 MICU and... success!
Mind you, it took >4 hours the first time to get the MICU out and 2 hours to put it back in. I did this at least five times. I got good enough at it that I could do the whole swap in less than an hour. Back and hands were not happy each time I did it for a day or two.
These cars have a Bluetooth handsfree module that goes bad and starts leaking power. The fix is to bake them in the oven at 350F for 5min to reflow the solder. Already did this twice and then decided to just get rid of it. So that was not the problem.
She needed to get back so we figured out which fuse was the easiest to remove and she lived with that for a couple of months. In the mean time we figured out it was the MICU module, which is the module that controls all the electronic systems and security. Without this nothing works. I was told a new one would be north of $1200 and labor. If they could find one. The dealership said they would chase down the problem again for $165/hr just to be sure... And I would have to leave the car with them until they were ready. Possibly 3 weeks.
I found a couple of the units on ebay for <$100. One was from a 2008 and another one that had some broken plastic on the case for from an early 2005 (same as my car). I tried the first one, nothing worked, all kinds of systems failed. I learned there was an EEPROM chip in the Honda/Acura MICUs that store the codes to make the systems work and are unique for each vehicle. The Dealership can program them for a fee. Having a full electronics lab, I swapped the chips in no time. It was better, but the starter would not engage. In desperation, I did it again on the 2005 MICU and... success!
Mind you, it took >4 hours the first time to get the MICU out and 2 hours to put it back in. I did this at least five times. I got good enough at it that I could do the whole swap in less than an hour. Back and hands were not happy each time I did it for a day or two.
Once you find the fuse that passes the highest current, why not just place a switch button in series with it? Turn it off when exiting the car. Add an LED to show when it is on.
This can be a problem with any modern car. I had a similar problem with my 2011 BMW, but I was partially responsible. I added a device to the CAN bus between the entertainment system and the rest of the vehicle so my passengers could watch DVDs while we were driving. When the vehicle was off, the ECU would stay awake trying to communicate with the entertainment system, which would fail because the device I added was powered off. The car was brand new and the battery died after a month. I removed (and redesigned) the device so it would provide CAN connectivity when off, but had my battery replaced (under warranty) before I re-installed it.
It sucks that auto manufacturers don't consider the consequences of their design decisions. A malfunctioning (or missing) entertainment system should not cause the ECU to drain your battery.
It sucks that auto manufacturers don't consider the consequences of their design decisions. A malfunctioning (or missing) entertainment system should not cause the ECU to drain your battery.
I had a parasitic drain on my Tacoma from my Automatic device (OBD-II reader / GPS tracker). I parked in a garage with no cell service and it drained the battery by constantly trying to connect. It was a non-issue when I commuted daily but started killing the battery when COVID happened and I switched to WFH.
Hard for mechanics to diagnose because they had no idea what that device was and also one of their first steps was to unplug it, put it in a cupholder, and plug their own OBD-II reader in.
Now the Tacoma is parked again most of the time because I got a Tesla and I'm noticing a voltage drop. I need to do more research, I don't know if this is normal for being parked or if there's a drain.
Hard for mechanics to diagnose because they had no idea what that device was and also one of their first steps was to unplug it, put it in a cupholder, and plug their own OBD-II reader in.
Now the Tacoma is parked again most of the time because I got a Tesla and I'm noticing a voltage drop. I need to do more research, I don't know if this is normal for being parked or if there's a drain.
We have a similar problem with a Lexus rx300 2001. The computer never goes to sleep. I was thinking of looking for (or making) a patch-fuse with a kill switch to stop the drain. Computer sleep depends on the flakey door controller switches.
A recent HN post mentioned that a signal like radar from a nearby airport can sometimes be enough to kick the keyless sensor module out of sleep mode and drain the battery. (This was the one about CAN injection attacks).
A few days later, we were visiting them. I looked at the car and saw the door closed, but not properly latched and ever-so-slightly ajar. You know, that half-closed thing car doors do when you don't close them hard enough.
It turns out someone, possibly my son, had been not closing the door completely. This did not keep the lights on or cause any other visible sign, as it would in some cars.
After I told them to slam the door fully shut, never a problem again for 2 years and counting.