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Hi all. Just wondering if any of you have any experience with battery drainage. I have a new battery and alternator in my 2001 w203 but there's something draining the battery while the car is turned off. I would leave the charger on for 24hrs and it would never reach fully charged status, and then the battery would be drained again within 2 days - I would have to disconnect the battery and then charge it so it would reach full.
I visited 2 mechanics who didn't want to attempt to fix the car, the third just ran a diagnostics test and put a new positive cable clamp on, which I don't think would address the issue at all if I'm not mistaken, though the positive cable seems a bit oxidised to me.
I bought a multimeter and learned how to check how much amperage was being used while the car was off. It registered as being about 2.7A, but as I began pulling out and checking the fuses and putting them back one by one, the amperage being drawn dropped down to 0.15A with every fuse in place. That's still too much to my knowledge (should be max 0.08A I think) but it's strange that it fluctuated so much despite me just pulling out and putting back in some fuses. I disconnected the multimeter and then reconnected to see what happened and it was the same thing again - drew about 2.7A and then after a few moments dropped down to 0.14A again.
Anyone had any experience with something similar? I'm gonna go try again later and check every fuse, just thought the fluctuation of amperage was strange.
Does your car have the infamous memory seat option? If so, see fix for modifying the wire harness. There is also the option of replacing the modules with the updated version (get the PN from your local dealer).
The car should draw under 0.05A in the fully quiescent state (obviously assuming the electrical system is fully stock). According to the dealer it takes 30 minutes to reach this state, but I found it happens in under 5 minutes. Different modules have different sleep timeouts, so the draw will fall in steps like what you're seeing.
Last edited by slammer111; 03-30-2022 at 05:55 PM.
Does your car have the infamous memory seat option? If so, see fix for modifying the wire harness. There is also the option of replacing the modules with the updated version (get the PN from your local dealer). The car should draw under 0.05A in the fully quiescent state (obviously assuming the electrical system is fully stock). According to the dealer it takes 30 minutes to reach this state, but I found it happens in under 5 minutes. Different modules have different sleep timeouts, so the draw will fall in steps like what you're seeing.
I took care of the seat memory fix, solved my issue with the battery draining.
I have never heard of the memory seat option before - but if I find that the fuse that controls the seats is the culprit for the battery drain, I will know how to fix the issue, so thank you.
Ah, that makes sense about the sleep timeouts for the different modules. I will give the car a little time to settle down on the weekend before I check the fuses again.
I have never heard of the memory seat option before - but if I find that the fuse that controls the seats is the culprit for the battery drain, I will know how to fix the issue, so thank you.Ah, that makes sense about the sleep timeouts for the different modules. I will give the car a little time to settle down on the weekend before I check the fuses again.
Memory Seats are powered seats, which have the option to store the seat setting for 2 to 3 drivers/passengers, depending on model and year of car. If you have this feature, I bet that your fuses will be ok and the problem is within the seat modules.
Memory Seats are powered seats, which have the option to store the seat setting for 2 to 3 drivers/passengers, depending on model and year of car. If you have this feature, I bet that your fuses will be ok and the problem is within the seat modules.
I see, and it seems I do have memory seats. So if I were to hook up the multimeter to the battery again and kept an eye on it while I unplugged the seats, if they were the problem, the parasitic drain would drop to 0.05ish, correct?
I pulled the above-mentioned cables from the seats and there was no change in ampere draw, so I don't think they're the problem. I pulled every fuse from the driver's side door with no issue, but can't really check the fuses in the trunk easily because it activates the trunk light which changes the multimeter reading. I will have to figure out how to get around that. By the time I hade finished checking the fuses, the ampere draw had creeped up to 1.15A after I had closed the trunk and it seemed to have stabilised there.
Unplug the trunk light to take it out of the equation.
Did you let the car amperage stabilize (more than a minute or two) before measuring? I would give it at least 5 minutes. As mentioned before, the dealer mentioned it can take up to 30 minutes. I assume this depends on the options installed.
Unplug the trunk light to take it out of the equation.
Did you let the car amperage stabilize (more than a minute or two) before measuring? I would give it at least 5 minutes. As mentioned before, the dealer mentioned it can take up to 30 minutes. I assume this depends on the options installed.
Yes, it seems I will have to remove the light as there's no pressure button that I can press to make it seem as if the trunk is still closed like there is with the doors.
And yes, I gave it 10-20 minutes before I started working on the fuses - there's a draw of around 2-3 ampere for a few minutes after connecting the battery, and then it dies down to 0.15A, which is the parasitic drain reading. I did find that after pulling some fuses and putting them back in again that the drain would jump up to 1.15A.
I checked all the driver's door fuses with no issue, so I'll check the fuses by the motor and in the trunk. I saw a YouTube video that also had a 0.15A drain on the same car and it ended up being fuse 8 in the trunk, which was the alarm I believe. Either way, trial and error should tell me what's up.
I have similar problem with my 2003 C240 USA model but the drain current is about 0.4A. I tried removing and re-inserting every fuse in all the 3 fuse boxes but none of the fuse helped bring down the drain current. Before this problem I could leave my car for 3 to 4 weeks and it will still start with out any problem but now it wont start if I leave it parked more than 2 days. I got a new battery, new alternator, and a new alarm siren (as it contains in-build battery, which if weak, leads to drain from the main battery.) I also removed passenger seat and driver seat power cables one at a time as well as both together, but it drops to only 0.35A only, which doesn't help. Before starting diagnosing the problem, I closed all latches on the doors, trunk, and for the hood and also pushed in the pins with clamps on all the doors which are supposed to be pushed in when the doors are closed. When I remove security alarm fuse the alarm goes off and I have to reactivate the alarm after reinserting the fuse before resuming diagnosing. I have tried this procedure 3 times over a week to make sure I have not missed any step in testing or any fuse. What am I missing? Appreciate any suggestion.
Start disconnecting the various branches from the main bus box(?) (the plastic box with the red jump point cover next to the battery). That will at least point you in the right direction.
Don't measure the voltage drop. Use an ammeter in series on each circuit, one at a time. A voltage drop won't tell you much at all for a low voltage DC system.
Last edited by slammer111; 04-16-2022 at 04:19 AM.
Thanks slammer111. I will try it tomorrow and report back. I did do a voltage drop test on all the 5 wires in this pre-fuse main bus box. The first one showed 0.1mV drop consistently measured between positive lug and the fist wire's screw, which to my understanding goes to interior fuse box on left side of dash near steering wheel. Other four points shows either 0 mV consistently or fluctuating between 0 mV and 0.1 mV.
I removed battery negative and then the wire from pre-fuse stud 1 as shown in the attached photos. To my surprise the clamp meter is showing 0.45A current on the disconnected negative wire for battery and I made sure to reset the meter as shown in the attached photos. This 0.45A current reading is very close to 0.42A when the negative wire for battery is connected to the battery. Is my clamp meter no good and I need to get a digital meter for current measurement with series connection? I trusted my clamp meter as its reading with clamp around the wire and with the wire outside the clamp and reset to zero were making sense. The drain problem exist in spite of these surprising measurements.
Thanks slammer111. With the digital meter in series the battery drain is 980mA. When I removed the power to passenger front seat, the current dropped to 77mA. I hope this solves the problem. Appreciate your help.
Technically the module can also be modified by cutting the corresponding PCB trace and adding extra solder to join the 2 pins. By doing it this way, you won't need to modify the harness, which would result in the cleanest look.
It's been a while since I tried diagnosing my problem - been disconnecting the battery after every use. Using this reading, 0.22 is still too high and it should be less than 0.05, correct? It was reading at 1.20 until I pulled fuse number 3 from the rear (dome lamp, right and left luggage compartment lamps and radio remote control receiver) at which point it dropped to 0.22 I thought maybe I'd solved the issue until now, but maybe I should try pulling fuses until it's less than 0.05?
FYI: There is a fast way to find parasitic drain. Measure the voltage drop at the fuse itself. Put the Multimeter to millivolts and measure between the two legs of the fuse. If it is above 0.1 mV, this circuit is suspicious. You have to wait 10 min after you opened/closed doors to let the computers go to stand-by.
03-30-2022, 08:58 AM
