I had parasitic draw from a 12v phone adapter that wasn’t powering down when the car was locked, took me forever to realize that cheap Amazon gadget was causing issues!
I fixed a parasitic drain on my car in 408 days
281–290 of 515 posts
Re: I fixed a parasitic drain on my car in 408 days
#282This 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.
Re: I fixed a parasitic drain on my car in 408 days
#283Had 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.
Name and shame, help your fellow HN readers out, no shame in getting a lemon!
Re: I fixed a parasitic drain on my car in 408 days
#284Earlier quoted context omitted.
I wonder if installing a switch to disconnect the car's battery entirely would be an acceptable (but obviously hacky) solution.
Not really, When powered down(battery diconnected) the computer then has to re learn parameters/pass internal validity checks. On a well preforming system this will be done in as little 1 or 2 rides but on a marginal system this can take many rides. the computer may not enter closed loop mode until these checks pass. closed loop mode is where the computer set it's output values(fuel air ratio, timing etc) based on it…
Yes, my Audi did not like being disconnected from power. If I remember correctly, it didn't go into limp mode but it was in some partial alarm state when it reconnected such that one had to mimic the Contra cheat code with their fob to get it to shut up. I jest, but yeah. Battery dead was not a condition with a transparent recovery.
Re: I fixed a parasitic drain on my car in 408 days
#285One 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…
Also 12v USB phone chargers that stay hot when the car is locked. This drove me crazy thinking it was a car issue draining the battery or alternator.
Re: I fixed a parasitic drain on my car in 408 days
#286Earlier quoted context omitted.
You can drive a car from the 90s before they started shipping alarms and keyfobs in every vehicle. My 1995 Miata draws just enough power to maintain the clock in the radio, and it starts just fine after sitting for 6 months (it's not a winter car).
My 2000 Ford Explorer has all kinds of electronics and modules from the factory. And even my crap I added in... I leave my Qi charger, ham radio, Bluetooth FM transmitter all running and plugged in, and I can come out a week later and the battery is still not dead. And when I'm camping I run a 12v van all night long. Truck starts right up every time. I don't get what would be draining more power than that in a more m…
A modern car is supposed to have single digit or less milliamp drain, according to a random car mechanic I know. I'm a mechanic but not automotive.
That's after being off for 30 minutes though. Some things stay on for a while.
Re: I fixed a parasitic drain on my car in 408 days
#287Earlier quoted context omitted.
Not great advice. Most new-ish cars also store the dinamic engine calibration data in ECU RAM so if you disconnect the battery you can find your engine running harsher next time. So are the values of the headlights auto leveling system and other stuff. You're also risking to reset the radio/media unit security code (on cars that aren't too new but also not super old), which if you got the car second hand and the form…
Not ideal to cut power to the entire car, but that happens anyway on every battery swap, no? If you want to get fancy you can isolate the exact fuse and switch just that: https://www.ebay.com/itm/175668177479 Thinking more, given how common parasitic drains are, carmakers should have all non-essential fuses in a separate subpanel section that can be easily switched off/diagnosed.
No. Good automotive mechanics plug a little 12v power supply into the OBD port before replacing the battery, to keep the ECU/radio RAM powered.
Re: I fixed a parasitic drain on my car in 408 days
#288Earlier quoted context omitted.
Ye olde ammeters were secretly voltmeters with a low-value but high-precision shunt resistor in series with the circuit to be measured. Current passing through the resistor causes a tiny voltage drop, which is measured by the meter. As the voltage is proportional to the current, the scale painted on the cardboard behind the needle did the actual conversion. In the author's setup the fuse takes the shunt's place; its…
Or you could measure the resistance of the fuse directly using a multimeter...
Not usually. It's too low for regular multimeters. You'll most likely need a 4 wire meter to measure that low of ohms.
Re: I fixed a parasitic drain on my car in 408 days
#289Earlier quoted context omitted.
> It seems like mechanics really don't like digging into the electrical part of the car... Tell me about it. I'm in a similar boat. My audi a4 has had a parasitic draw for the past 10 years. My mechanic didn't want to take the time to address it because that sort of thing takes a serious amount of time and he's always backed up. I got out my fluke and narrowed the cause to what I believe is the comfort control unit.…
Probably should get a brand more reliable than Audi...
After my Audi I learned I'm never buying another German car. Hard to work on myself, absurdly expensive for the shops to work on them, parts are very expensive. Since most owners seem to be "of a demographic" that does not mod/repair their vehicles, the online community pales compared to some other brands where this is a bigger part of the ownership culture, IME. Yes, I know there are passionate Audi modders and repair forums out there, but I'm referring to a percentage of the ownership base and in comparison to communities around other makes.
The Audi was great fun to drive though, no denying that. Just different priorities in what I want out of a car.
Re: I fixed a parasitic drain on my car in 408 days
#290Good troubleshooting. More of a workaround than a fix, but quite possibly good enough. I do wonder what it would need to work as designed though. Is there a dedicated ECU for the keyless system that that harness connects to?