Hi Ray,
Thanks for the update and the additional information. I really am extremely sorry for the delay in coming back to you as I know how important this is for you to get the car repaired, but as you know most of my time these days really is accounted for with work commitments, roll on the end of July, I’m actually counting the days down now and not the months. This is going to be a long post Ray, so hopefully I am going to try and put everything in to perspective and cover all that you will need to know and do. I would suggest that you cut and paste this on to a word document and then print it off so you can refer to it later on when on the car.
Before you do anything on the car though, read over this post several times so you can familiarise yourself with the context of exactly what I am saying and in particular when you do come to use your multimeter, its important that you give me the correct data. I will guide you through the process of using the multimeter on what to select, the appropriate range and scale as and when we come to check the car later on. If you wish, you can also still use the other ammeter that you bought and place that in series with the battery and the battery lead if you make up a couple of small jump leads, you can also use it for final clarification once we have found the issue, hopefully, at the end of all this you will have found it and its causation.
I have noted what you have said in your last post and this is encouraging news and not as bad as originally thought. When you refer to the present current drain fluctuations, they are still far too high and inconsistent and there does still appear to be an issue here. The only ones that appear to be in the acceptable range limits are the 0.030 to 0.040 amperage range, which is consistent with what they should be in a stable condition. The modules on your car should have shut down completely within the hour and should not have taken any longer than that. In one of my earlier posts, if you look back at it, I specifically mentioned the fact that some modules, although they do go in to “sleep” mode, do have a tendency to awaken again, these are by far the most difficult issues that anyone could have when trying to diagnose any form of parasitic drains. We refer to it as a “phantom” drain, and as the name implies, they do come and go and no reasonable explanation at first as to why, on that basis, the systems needs to be investigated and the problem is that we need to find it when it’s present to identify the module, or indeed if it is a module. The engineering term by the way is correctly named as MPPD’s (module parasitic phantom drains).
Normally, I don’t ever get involved with this type of work anymore, but under similar circumstances, I would generally have just put my own laptop on a vehicle so I could closely monitor the active/inactive status of every module on the car. I’ll briefly explain, when a module goes in to “sleep” mode, each and every module is then given a status of zero, zero meaning off as in “sleep” and the time is recorded and is monitored over a period of time, if, for example, a module awakens, this is denoted by a number one status, the time is recorded again until it then goes back to sleep, if indeed it does go back to sleep, this is then recorded and denoted as a number two status and again the time is recorded. This process continues over many many hours, sometimes over a 24-hour period and covers every module on the car and can only be done under certain conditions. Its not practical or even possible for us to watch the car for such a long period, but what we would do is to leave a laptop connected which will in fact do the work for us.
Its equally fair to say that some modules are specifically designed and programmed to awaken to monitor the system actually under its control, pretty much like your own PC at home would do if you have a calendar with a specific reminder date, an example on a car would be that of an active air suspension system, where the height and attitude of the vehicle is monitored and evaluated through its various strategically placed sensors. However, in the real world, such as your problem at the moment, its not always possible or practical to replicate that scenario, so we adopt another approach but as with any type of vehicle diagnostics, especially electrically related, these need to be visually monitored with the use of electrical test equipment such as an ammeter, lab scope, etc., as you don’t have laptop or the software at your disposal to do this.
There are many ways in which one can carry out parasitic drains tests, to which I have only named a few on an earlier post which are the most widely accepted and used in the motor repair industry, some are relevant and others are not, some are more accurate than others. What we tend to do is to be less invasive in opening up a circuit if it can be avoided. Even when you do open a circuit up, there is always the possibility that something adverse can go wrong, modern motorcar electronics are very susceptible to voltage surges and as such can in fact damage sensitive electronic circuitry. I’ll cover and guide you through a test later and you will always find it very useful and easy to do without subjecting the car to any risk of damaging any of the electronic components, although it would be equally fair to say that there is no such thing as being 100% risk free when working with electronics, but this test is in that regard is a non-invasive test and we don’t actually need to open a circuit up to insert an ammeter to measure the quantity of any parasitic drain, we evaluate this through the voltage dropped across the circuit/s.
With the greatest respect here Ray, the last thing you should ever be doing is pulling fuses and relays out from circuits that are actively live, this really is bad practice and not one that I would normally advocate or endorse unless it was absolutely essential and necessary, which may very well be the case if some test methods don’t produce the results. Unfortunately, this method of approach has long been established and practised in the absence of not having the equipment to test the circuit fuse and it would be extremely difficult to convince people otherwise now.
There is no need to pull fuses out if you understand how to use a multimeter properly and you are familiar with the circuits under test. A very simple millivolt drop test over a fuse is sufficient enough for us to qualify and quantify its electrical integrity if current is actually flowing in that circuit and the amount of current present. Yes, there are calculations to be done here but this is beneficial and certainly outweighs and avoids causing any issues. Most people just pull fuses at random and are not aware of any potential consequences, and why should they be; they are not trained in vehicle mechanics or electronics, so they do what they have always done and what they read and learn about from the Internet.
You would be surprised at the amount of damage one can actually do by just pulling fuses out of circuits unnecessarily. If you read my earlier post, (and I am certainly not being critical of you here Ray) you will see that I asked you to wait whilst we monitor the circuits first and I did that for a very good reason. I’ll ask a question of my own here, would someone deliberately pull the plug out of their home PC when it was switched on, the answer I would expect them to say would be no, then why on earth would someone do it on their motorcar, its no different. To remove a fuse from a circuit with current flowing will only exacerbate the problem, most people don’t know that when the fuse is reinserted the module boots back up, just like a PC would and starts the process of at the beginning again, only in our case, this just adds addition current back in to the system that we are tying to monitor for excess parasitic current, it really doesn’t make any sense to me at all, and yet, I see people do this on a regular basis.
There are occasions when it is absolutely necessary to remove fuses or relays, an example of this would be the fuse removal on the PSE module, to reset this module, following the time out facility, that’s exactly what should be done and it should be disconnected from its power source so it will lose its short-term memory and start the process off again at the beginning. These modern motorcars today are not like they were 25 or so years ago, and when something goes wrong they are extremely expensive to repair. Believe it or not Ray, but you do really have one of the most advanced and complicated motorcars that Mercedes Benz has ever built, and I kid you not when I say that, the amount of electronics and equipment on your car is phenomenal and when dealing with them one has to be extremely careful.
Ray, I don’t like to ask you the question here, but I am going to ask the most obvious question that I get asked on so many occasions and the answer I give to them still applies here. Have you actually checked over the car to see if anything has been left on, no matter how insignificant or trivial you may consider it to be? Things such as vanity mirror lamps, door exit lamps, centre console lamp, yes there is a light in there on the CL’s, even down to the cigarette lighter element being detached from its housing and sitting in the bottom touching the electrical contacts, they may all sound really silly and trivial things to check, but in reality it really does matter, this is a common sense approach before considering anything else as often it usually is something quite simple.
Has the vehicle ever had anything else fitted since you bought it Ray, such as a tracking system device, phone or anything of that nature? The only reason I ask these questions is that the parasitic drain now appears to be quite low in comparison to what you had initially, which was 2.4 amps, (2.400 milliamps) which to me would now indicate that whatever is drawing the current at the moment is consuming approx 0.060 amps over and above what we are expecting to find as a normal acceptable parasitic drain. A parasitic drain of 0.060 amps if measured across a standard 10 amp fuse would only represent a voltage drop of only 0.5 millivolts, which is half of one millivolt. If you are happy that everything possible has been done and checked on the car, then we can now start to look at the systems.
We can start anyway with checking if the vehicle has a short to ground first because this will form the basis as to where we can go from here. Start by removing both the battery leads off the battery, negative terminal first and then the positive lead. Leave the leads off the battery for about five minutes or so and then connect the leads together, keep them together for about a minute or so, I actually just use an elastic band for this purpose. The reason being is that we want all the capacitors to drain down, its not important for you to know why at the moment, but I will explain all that after we repair the car, but before we do the next test the system must be completely isolated of any form of voltage/current source.
With your multimeter, select the 20 ohms scale range only at the moment and place the test leads in the appropriate jack plugs, black to the common socket and the red in the volt/ohm/milliamps socket. There is no Delta zero facility on that meter Ray, so we will have to take that in to account when we do any calculations. Hold the multimeter test leads together first and then read off the ohms scale, on your meter it should be reading 00.1 - 00.2 or thereabouts, depending upon its accuracy. Whatever the reading is on yours, that figure is referred to as “above” Delta, so when we test any circuit we can deduct that figure from our final figure.
With the battery leads still disconnected from the car, put your multimeter leads across both the positive and negative battery leads. The reading you should get is a considerably high resistance value depending upon the specification of your car. Set your meter on the 200Kohms range scale first or higher if necessary and if you get a reading similar to the reading you got by just connecting the multimeter leads together, i.e., - 00.1 - 00.2 or thereabouts, then that indicates we have a short to ground somewhere, possibly an alternator diode fault or a relay may be stuck, in some cases, unfused circuits shorted to ground, it could be anywhere and on any circuit at the moment Ray.
If everything is OK up to this point, which I am pretty sure it will be given the amount of parasitic drain you have and a very high resistance reading over the battery leads, then make a note of it and let me know what it is so I can make some calculations later, now reconnect everything back together in the reverse order, positive lead connected to the battery first followed by the negative lead. It’s entirely up to you at this point if you wish to re-synchronise all the windows and sunroof again. Start the car and let it idle and just run through the general operation of the vehicles systems, lights, indicators, horn, etc. I am not convinced that you have any short circuits on balance because of the low drain but I am just checking every possibility here Ray and don’t want anything else to influence the readings we are about to get when we come to test the circuits.
The next tests Ray are extremely important, if not “the” most important and the voltage drop data recorded from your multimeter has to be accurate as there is a specific formula that I will have to calculate on your behalf based upon the test results obtained. The test is a completely non-invasive test, which means that no part of the circuit’s integrity has to be compromised here during the test. We can then go on to test the individual relay circuits after doing the volt drop test where we are measuring the millivolts dropped across each individual circuits fuse. If any readings are high, then I’ll convert them in to milliamp drains once we have a stable baseline figure of parasitic drain.
At the moment it appears to be very unstable with the fluctuations you referred to. I need to identify the total amount to give me some idea as what may be drawing such a high parasitic drain level. It’s not possible to do a millivolt drop test unless there is current actually flowing in a circuit, and if there is current flowing in a circuit, irrespective of what that current level may be, then that means that the circuit must it be switched on and is consuming power, which is what we now have to ascertain and this is probably where the problem will in fact be. There is a vast amount of circuitry on a W215, not to mention how many modules are on the car, in fact some modules are specifically known to failure, such as door modules, seat models, even the CD players have issues, something worth considering here Ray by removing the cassette pack from the CD player before you do any further parasitic tests. Even the wiring harnesses in to the doors from the cabin have major issues with mechanical breakages here on the CL’s, something which we may have to check upon later.
Before we do any tests, switch on the lights for several minutes to remove any surface voltage from the battery, let the readings settle down and then make a note of the battery voltage and also the resistance value from the test we did earlier on the battery leads. At the beginning of the post I suggested that it would have been advantageous to have two multimeres, if you haven’t got two Ray, then we will have to use the one. On your multimeter, you can now select the 200m millivolt range only, (we can scale up if necessary) and we can measure the voltage dropped over the fused circuits first, if any of them are active, then current will be flowing in that particular circuit which will give us a millivolt drop reading on your meter.
Do all the tests as outlined Ray on every single fuse that you can possibly gain access to. Do not remove any fuses at all until we find the culprit, if you look on the top of each bladed fuse, then you will see two very small holes that you can put your multimeter test leads across to measure the millivolt drop. Make sure you have a good contact on them with your meters leads, if need be, then lightly sharpen the meter probes to a point. Come back to me with any high figure results and I will calculate and convert them from millivolt drop values to milliamp drain values. Please take your time Ray in doing them; there is no rush and if necessary adjust your meter range to obtain the best possible value. I appreciate that all this is new to you and it will take up quite a bit of your time. When dealing with fluctuating parasitic draws that you have, then the only way to deal with them correctly is as I have outlined in the above unless you have a laptop to work with. Here is an example of what we are actually looking for Ray, which will give you a better guide and indication as to what is going on and what values to expect.
Example - I’ll use the circuit for the AAC system here Ray. When you do a millivolt drop test on fuse number 82, the millivolt drop that should be obtained should be less than 0.1 which is in fact a tenth of one millivolt and that figure alone actually represents a parasitic drain of 12 milliamps (0.012) across the fuse, which is still in excess of what it should be when that module alone is in sleep mode. This module when in sleep mode should only draw approx 4 milliamps, (0.004) which you would not be able to detect using the millivolt scale range on your multimeter, therefore, you should see and be reading absolutely zero on your multimetre in the millivolt range scale, if you see and monitor a reading of zero, then the circuit is functioning properly meaning that there is no current flowing which would be represented as a voltage dropped over the fuse when testing. That particular module is in sleep mode and the very low current drain of (0.004 amps) current being drawn is in compliance with its own parasitic limits. If you place an ammeter across the terminals in place of the fuse, then depending upon the accuracy of your ammeter, it will actually register in the very low milliamps scale range only.
To do all the tests that I have outlined properly, familiarise yourself here in the procedure in setting up the car prior to doing any tests, open the bonnet and press down on both the n/side and o/side bonnet locking catches, the alarm microswitch is also located here on the o/side catch if you wish to arm the car alarm later and add that in to the equation, open the boot lid and close the locking catch mechanism as previously noted, push in the door contact switches, the ones for the short stroke window operation, secure them in place Ray with some type of blunt object, open the drivers door and let the seat move right to its end travel position and leave it in that position until you have finished the testing, you will also need access to the n/side fuse box here so its best to do it now to save doing it later during the tests and finally, close the o/side and n/side door locking catches in to the locked positions, the same as you have done on the boot lid and then lock the door with the blade key. Its quite a lot to remember Ray but once this is done wait at least 45 minutes before you touch the car.
Now that you have done all that Ray, you have the freedom to move around the car unrestricted so you have full access to both the n/side and o/side front fuse boxes under the bonnet, the n/side fuse box at the side of the dash and the fuse box under the o/side rear seat. The last thing you want to be doing at this stage is introducing additional current flow in to the system when you are trying to find a parasitic drain, so doing all this beforehand is less likely to be an issue, especially if you have already inserted the ammeter in series with the battery. I am pretty confident that you will find this Ray if you do everything that I have stated, all that is needed is a common sense approach. It’s really just a matter of patience and unfortunately it takes as long as it takes. Diagnosing electrical issues can in fact be either straightforward and relatively easy to find, or it can test the most skilled individual at times when you have issues as you have at the moment. If all the above doesn’t reveal the identity of the fault, then its even easier when it comes to isolating individual relays and modules, but lets see where this takes us first Ray, we can only do so much at a time.
At the beginning of the post Ray I stated that at the end of it we should be in a better position to make some form of judgement and/or conclusion from all of what we have covered and gone through to date. The reality is this; we have established that we now have a figure of 0.060 milliamps drain over and above what we would like it to be which is 0.047 milliamps at its maximum. So lets consider this for a moment, if for example, that 0.060 milliamp drain was just on the one circuit alone, then we would expect to find a voltage dropped across that circuit of just under half a millivolt. However, that voltage drop and parasitic drain could very well be shared amongst several circuits, modules or anything else on the car come to that matter. When dealing with very small current drains such as this and nothing obvious comes to mind, this is where we have to be so precise with our measurements and these are very easy things to miss for an untrained person, and that comment certainly isn’t a criticism here Ray, on the contrary, I can’t commend you enough for taking on the task and challenge and its because of this very reason that I genuinely have afforded you my time and I will continue to do so until you are happy with the car. Also, what I think you will take away from all of this is the fact that you will see the distinct benefit of measuring the systems now by the volt drop method, not only that, but you have an advantage here over any type of measurement system available. You can measure the before and after voltage to actually see if a system has indeed been shut down and gone in to “sleep” mode.
Continued.......
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