Battery Parasitic draw test?

Hello, I wouldn't put your meter in series with the negative cable until you know how much of a draw you are having. You could burn your meter up if it's not fused. I'll explain the proper way to find a draw using the voltage drop method, but you need to prep the vehicle first.
Since you need access to all the fuse panels in the vehicle, but you still need the vehicle to go to sleep (if it will), all the door latches and hood latch need to be closed so when you lock the vehicle it will start to power off modules(go to sleep), then you can test for any voltage drop across fuses. I'll look up where all the fuse panels are, and what latches will need to be closed for it to power down. These vehicles have a ton of modules in them, so it can be any one of them staying awake or waking up a network causing a draw on the battery. You're going to set your multimeter on DC volts, but testing for very low voltage drop, in the mv (millivolt) range. This indicates current flow across a fuse.
You will need access to the trunk, engine compartment, and interior fuse panels. So you're going to have to make sure all of those latches are latched so the vehicle can lock, and then the modules will start to power down. It can take a while for all the modules to finally go to sleep. It would be best to use a low amp clamp around the negative battery cable to monitor current flow. That way if this a few amps draw it won't burn your multimeter out. How fast is the battery losing power?

Is this the CLK500 Cabriolet model?
Either way, you will start by latching the door, trunk, and hood latch (if it has one). But leave the doors and trunk lid open so you can access the fuse panels in those locations. Then you will need to lock the vehicle with a key fob if you have one. This way the vehicle will start to power down its modules. And eventually go to sleep. It can take an hour or more depending on the vehicle to go to sleep. When it has gone to sleep, that's when you start to check fuses for any mv voltage readings, if there is voltage drop on any fuse, then there is some current flowing on that fuse.

Note*
Pulling fuses to check for a draw is not the correct way to check, because once you plug that fuse back in it can wake up the vehicles network again and you have to start all over.

Also, if you notice any components that are not working correctly, i.e. window switch, radio, heated seats, HVAC stuff, etc., those are areas that might be causing a draw while the vehicle is off due to a malfunctioning component. Parasitic draws can be one of the most difficult issues to find, especially in a Mercedes or higher end vehicles because they have so many modules. This vehicle has 4 pages of modules.


https://www.2carpros.com/articles/how-to-use-a-voltmeter

It's a convertible. so, go ahead and tape all door latches and trunk and lock it with the key and keep doors open and then place ohmmeter to DC and start pulling fuses?

No, you don't tape the door latches, you need to push them in so that latch like they would when you normally close the doors. This way the module that monitors the door latch switches thinks they are closed and locked. I use a screwdriver and just push them in. They should unlatch when you pull the door handle, same as when you would go to open the door. You're just tricking the module so that you can lock the doors and set the vehicle into its power down mode. The modules in the vehicle won't power down if the doors or a trunk latch are open. If there are actual switches that the doors push on when they close, such as ones that may be in the doors' flame, then yes those need to be pushed in and held in by some means. I would think a Mercedes has switches in the door latches, but I don't work on them much.
You need all the interior lights to power down as well. Then lock the vehicle with a Fob if it has one, that should set the security system, and modules on the networks will start to power down as they normally would.
The tricky part about parasitic drains is that if there is a module that is staying awake, or waking up periodically, it can cause other modules to wake up.
But get the doors latched that you need open to access fuse panels, lock the vehicle, and give it an hour at least to start powering down. Don't leave any scan tools hooked up either, that will keep the network active as well.
I'll see if there is any specific time for Mercedes modules to power down. Having an amp clamp on a battery cable will tell you the draw, it can also help you to know when modules are powering down because current flow will go down.
The next thing you're going to check is voltage drop across fuses, set the meter to DC volts on a mv(millivolt) scale. And just go across each fuse. When everything is powered down you shouldn't read any voltage drop across a fuse. If you read 0.020v(for example), that's voltage drops across that fuse, and there is current flowing through that fuse. This eliminates pulling fuses. But you need an amp clamp on the battery to know what the current draw is when the vehicle is powered down. And in a case like this, where the vehicle has a ton of modules, I will also have an oscilloscope on the CAN bus network monitoring activity. There shouldn't be any. And I'm willing to bet there is module staying active on the network.
You can also use a thermal camera to look through the vehicle and find areas staying hot, that also helps to determine which areas might be drawing down the battery.

How fast is this battery draining? Is it overnight or a few days?

Watch this video, he goes over a basic parasitic draw test. This will give you a better idea of how this test works. This is very helpful. But its basic, not addressing module issues,
There are also a couple TSBs on this PASS system causing a battery drain due to it needing a software update. These types of issues are very difficult to diagnose because this is a subscription based wireless system, The PASS system will keep the CAN bus network awake because it's trying to update but it's not able to, and this can cause multiple modules to stay awake on a CAN bus type network.

https://www.youtube.com/watch?v=lRcj1fQcWwU

New battery drains overnight. Can you recommend an amp clamp that is not complicated to work with?
Also, you mean latch all doors and trunk and then insert a metal key in door and lock doors but keep the doors open so I can access the fuse boxes?
Set ohmmeter to where it says V and 200m?

You can get a cheap amp clamp from Harbor Freight. If the battery is draining that fast, then you have something that is pulling a few amps at least. It's not just a small milliamp draw. That's why I was cautioning you about putting your multimeter in series with a battery cable. Most meters have a fuse, some don't, but you can only take an amperage reading for something like 15seconds and then let the meter sit for 15min before taking another reading. One of my multimeters has a 10amp max current check for a maximum of 15seconds, or it will burn the meter right out. So, an amp clamp will read the current flow by measuring the magnetic field around the wire. Thats why you just clamp it around either the positive or negative battery cable. Usually, the negative cable will be the one wire you can get a reading from because there's always multiple positive cables and you need to get a reading of the full current flow from the battery, Ill check Harbor Freights website and post one that looks easy to use. With a draw that large you're going to see it right away. You can set the voltmeter to 2volt scale, that just means it will read up to 2volts, if it's a few decimal points down, switch it to 200mv. You get the hang of it. The real purpose is just to see if there is any voltage drop. And yes, you'll need to lock the vehicle to get the modules and networks to shut down. But that might be the issue here. Let's find out how much of a draw you have first, then we can go from there. It might be something like an amp for the Radio that's staying on, those draw a lot of current flow.

It looks like Harbor Freights amp clamps are mostly high amperage AC clamps. You need one that is for lower DC systems. Accurate automotive amp clamps cost more because they need to be able to read lower amp settings. I have 2, one is an AESWAVE 20/65amp and the other is a Hantek 650Amp which is used for relative compression tests, but both of these hook up to my oscilloscope.
It looks like Harbor Freights amp clamps are mostly high amperage AC clamps. You need one that is for lower DC systems. Accurate automotive amp clamps cost more because they need to be able to read lower amp settings. I have 2, one is an AESWAVE 20/65amp and the other is a Hantek 650Amp which is used for relative compression tests, but both of these hook up to my oscilloscope.

You want something like this, easy to use, you can see here hes got a 5 amp draw, it has wide jaws to reach around any thick battery cables. It doesn't matter if you are on the positive or negative side. Current will flow. Just make sure whatever you get it says DC current clamp.

Nice, I will order one then go from there. thanks

Okay, if you find a very high current draw, you can also check the temperatures of components, because something pulling high current flow will be warm and show up hot with a thermal camera or temperature meter. Do you know if the vehicle has an Amplifier that goes with the Radio? I'm seeing the option in the service info Sound Systems for the Convertible.

And are there any codes set in any modules?
These are the Radio with an Amp diagrams, there are 3 Wake Up wires as well as CAN bus network wires to the Radio, so if one of these is staying powered up, it can wake up the Amp and CD changer as well as these Antenna Amp modules. This would pull a lot of current flow.

Watch these 2 videos, they are of a Mercedes with a battery draw, its part 1 and 2, but just so you can get an idea of what I mean when mentioning modules going to sleep. And why we monitor the networks in some cases to see if modules are waking up other modules. This tech is really great, very smart guy.

https://www.youtube.com/watch?v=5OE3CYNSVNI Part 1
https://www.youtube.com/watch?v=3lUBPH9l3nA Part 2

Also, I remembered that the hood has 2 latches, when i open it only one opens first then the second pull releases the other. When the hood is closed i still get the hood open message. But even if, when car is shut down that should not draw any current i would not think.

The hood latch itself will not be the current draw, but it can keep a module awake on the data network. Gotta remember that the hood latch signals a module, and that signal eventually ends up signaling the Cluster to display that message. I would start there. These Front and Rear Sam modules act as Body Control Modules in these vehicles in some cases. But since you've already noticed the hood latch, thats where I would start. There are so many modules in this vehicle its amazing, even for a 2004. Service info only shows a mechanical latch for the hood, but if theres a message for it, there has to be a sensor/switch somewhere to trigger that warning lamp, And its definitely being broadcast on the CAN bus network if its a message being displayed on the Cluster and not just a warning lamp..Id have to search through the oem diagrams to find the hood switch and what module it signals, But Im not too familiar with these diagram types. Its probably the Front Sam, but Im not sure on that yet. There are 3 or 4 CAN bus network pages, Ill post them later for you to see.
See if you can find a data PID for the Hood latch state with a scan tool

What is an acceptable voltage drop per fuse?

Battery was drained when i git the car. Battery in it now is new, so am sure there r ton of codes. Ill do a can scan and attach photos of codes left. There was a billion code most for low volts. This is what is left.

Also hood latches only have one sensor which isn't on the side that was a bit stuck. I made sure sensor is attached to harness and adjuster the little silver piece which it pushes on it as i read its common, if doesn't fix it then the sensor is bad. If i jump the connector to see if light goes away does that mean the sensor is bad?

I would unplug it and check for continuity when pressing it instead of jumping it out, Since we're not 100% sure on its operation, if it has continuity when pressed and then goes OL when open, the switch should be ok, you can check one of the wires for voltage with the key on, I don't even see any hood switch in service info, which is common. If you don't read any voltage on either of its wires you can try jumping it out at that point, But I think you'll find if it has continuity, the switch is not the issue, most likely one wire will go to ground, or grounds through a module to signal the hoods shut. If you read OL on the meter, you can try jumping the pins, but I'm hesitant on doing that without knowing its operation. You don't want to ground it if it's supposed to have some resistance to it, you might be shorting a module to ground. I'll look again for service info, but I didn't see anything before.

This is the hood switch I see in service info, is this what you have?

Yes.

So far, all I've found with a label of S62 in the OEM diagrams is this latch switch here. Which was under the Grounds diagrams, maybe this U82 is the Module ID. The aftermarket diagrams do not show a hood latch at all, the latch is on a ground circuit, the trunk latch is not even called a latch.
It looks like the Hood switch is part of the Anti-Theft System and is on the CAN B network, so if that switch is not in its proper state, I'm sure it will keep that network awake.

I'll check the fuses and the draw once the clamp arrives. What is an acceptable voltage drop per fuse?

You don't want any, if a fuse has any voltage drop at all there is current flowing, this is the chart that shows how much current is flowing according to the voltage drop across the fuse. Since fuses come in different sizes, the resistance for each size will be slightly different, and I mean very slight. So, for example, on a standard 10-amp red fuse, if you measure 0.1mv across that fuse, that means that 13amps of current is flowing on that fuse. This is an extreme example just to give you an idea, you will come across a fuse that is reading something more like 0.041 on that type of fuse which is about 5amps of current. This is all based on Ohms Law. I've added in another chart which deals in lower amounts of voltage drop. And a link to the PDF where the 2nd set of charts came from. But we will know more when you get your amp clamp and can get an idea of how much draw there actually is. I'm going to have another Technician chime in here, Steve, because he works on Mercedes and will be able to give you some better direction as to what might be some things to check right now. I'm just showing you the best way of finding a draw without having to pull fuses, because that method is only going to give you skewed results and could send you in the wrong direction.

https://caravanchronicles.files.wordpress.com/2018/10/fuse-voltage-drop-table.pdf

So any volts above 0 on any fuse are current draw?

Yes, if current is flowing there will be voltage drop. Thats how Ohms Law works, if you know the voltage and resistance of a component you can find the current. And the other way as well. But you have to make sure that the vehicle is set up for a parasitic draw test. You don't want to chase a current draw that is happening because of a door or trunk switch that is not properly closed. Are you finding more than one fuse with voltage drop on it?

How can a 10 amp fuse have 13amps of current going through it, will it not blow?

That is just an example from the voltage drop chart, I'm not saying there is 13-amps, I'm saying that is the amperage for that amount of voltage drop that would be across that size fuse. Just an example of how to read the chart.

Oh, i know that. I was just asking why would a fuse have over its rating current from the chart? I did learn about ohm's law in college and aware of how it works, it's just different when you apply it, lol.

The 2nd set of charts is better since it shows lower voltage drop readings that you will end up encountering. The first chart does not look good like that. It's just that the resistance across a fuse is so low that it will be a few decimal points back from zero, but even that little amount will reveal current flow and that's why it's a good test, you don't have to disturb any circuits to check their current flow. In some cases, if you move a wiring harness around you can accidentally move a wire and fix the issue, that happens a lot with shorts to ground. And then you can never find the issue again. So, these non-evasive tests are the ones you want to stick to. The amp clamp will help a lot too. When used with an oscilloscope you can check for shorted ignition coils or solenoids by just clamping on the feed wire and looking at the waveform to see if it's irregular, but that's a whole other learning curve.
With the amount of current you're losing, hopefully it won't be too difficult to find.
Did you figure anything out about that Hood switch yet? It's definitely part of the security system.

Hopefully. No have not yet figured out the hood switch. I am going to clamp the negative cable when i get the clamp today and disconnect the wire from switch that should tell me if the amp current drop at battery cable right? If not, am confused on when i remove it do i keep the wire connected and probe the 2 wires from back?

Also, if i connect the battery backup while it's full and then open all doors and lock latches and wait 2 hours for all modules to sleep the battery is still going to drain a lot in these 2 hours so what indonto keep it charged?

now, the hood switch is an input. It's not causing the draw on the battery itself. The security system is seeing that the hood is open, hence the message you're getting on the cluster. Whatever module is responsible for the security system is going to stay awake on the network until it sees all the required inputs in their required states (such as doors closed and locked, trunk switch closed, hood switch closed, etc.,) then each system in the vehicle will start to power down, and eventually go to sleep. The CAN bus network's activity will stop. But that can't happen until the vehicle can be properly locked, and after an hour or so the security module will time out and shut down as well. This is where the larger current that draws on the battery will go down to a few milliamps. You need to figure out why the Hood switch is displaying that message to begin with.

No, the hood shows open only if you start to drive. While doors are open and turned off it does not, and no messages appears i locked all latches and tried and locked it with the fob and it locked fine and the little red blinker was on.

Well, you need to see how much current flow is there after its locked up, you can keep a battery maintainer on it to keep the battery up to at least 12.6v. Wait an hour and check the draw on the battery. You should see the current flow keeps decreasing to below 50ma. If after a couple hours you still have a few amp draw, then start checking fuses. Thats going to get you to the circuits on that fuse that could potentially be the draw. Once you get to that point and have some direction, you'll need to start isolating those circuits. This is why parasitic draws on modern vehicles are so difficult. Mercedes, BWM, and other high-end vehicles are even more difficult.
Has this vehicle set any codes or had any codes when you first got it?

battery was bad when I got it like real bad, so I put a new one and I have done several CAN scans with nothing that can pinpoint me to anything. After the new battery all codes were deleted and was all good. Can I keep the tickler charger on it while the battery cables are still connected to the battery or better to keep a jumper box connected instead while I wait 2 hours for it to go to sleep?

If you end up with something like a 5amp draw or some other crazy high number like that, these are the 4 CAN bus connectors and all the modules throughout the vehicle, you can try plugging modules and see if the draw drops down., Starting with the radio if it has an Amp. You might get lucky if the draw is really high, which sounds like it is. The OEM diagrams are really difficult to read for this vehicle, we will end up on this vehicle for a year if we go by those. But try the amp clamp out when you get it. See what different current readings you get when you open a door, or turn the Radio on, just to get an idea of the different readings. You can see there are so many modules.

It's better to use a battery maintainer that can control the amperage and you can set a certain voltage level. A battery maintainer will also have a read out of how many amps the battery is pulling. Trickle charger are really only to maintain a battery over long periods of time, not hooked up to the vehicle.

It was charger a day before and i woke up to find it at 2.8v, lol.

Any battery maintainer that is basic that you recommend? I have 2 battery chargers but i doubt they will maintain. I always invest in tools since i buy and sell cars since it shouldn't be a problem. I always have cars that need a parasite test. Believe it or not i have 3 now and all are Benz lol. Yes, i know so many modules to deal with. I suspect the HVAC but will see what i find. I say that cause when i turn the car off i hear something ticking behind the dash.

Topdon makes a really good maintainer, you can set the voltage and it has a nice display that will actually show how many amps the vehicle is pulling.
Here's the HVAC fuses, if it has rear HVAC, there is a 40amp fuse for one of its "hot at all times" circuits. Pull those and see if the battery drops off. You could probably check the battery every few hours and see a difference. Even looking at the HVAC there are so many modules just for that system.

Wow, Topdon is so high, in the range of $700.

yeah, quality tools cost money, but if you're going to need it a lot, you need something that's not going to cook batteries. But shop around, you want a maintainer though when doing diagnostics, low battery voltage will cause issues that may not really be an issue. And it's extremely important to maintain battery voltage when programming.

If i have it correctly connected around negative cable and if aittinfs on clamp are right am getting fluctuating readings that started at 24 and then went up and stayed around 0.382.

One of the fuses if i pull it the amps drop from 52 to 23. It's a 7.5 amp with this reading.