December 23

2005 Mercedes-Benz E320, Electrical Diagnosis and Repair



Mark: Hi, it’s Mark from Top Local, we’re here with Bernie Pawlik of Pawlik Automotive, Vancouver’s best auto service experience. They’re 16 time winners of Best Auto Repair in Vancouver, as voted by their customers. How’re you doing Bernie?

Bernie: I’m doing very well this morning.

Mark: So you had an issue I guess with this weeks car repair of the week, is a 2005 Mercedes Benz E320 that had some electrical issues. What was going on with this Mercedes?

Bernie: Well there were a few things. Some interesting things. First of all the vehicle was brought to us because the owner was concerned about some rodent chewed wires under the hood, he was also concerned that his battery would go dead over night and there was a couple of dash lights and lights in the vehicle that remained on, the gear shifter light and a couple of other things stayed on. So these were his concerns. So we proceeded to have a look at them and do some diagnosis.

Mark: So that sounds like a number of possible things occurring, so where did you start?

Bernie: Well where we started first was a visual inspection under the hood of the rodent chewed wires and fortunately it turned out that it was really minor. They just nibbled a little bit on the outside of the insulation of a couple wires and we taped it up and it was fixed and done and that had no cause for any of the other concerns in the vehicle. The next step was to put a diagnostic scan tool up and do a full vehicle system scan. You can scan all the modules of this vehicle, a lot of modern cars give you that capability and you can scan the whole car, we do that a lot in diagnosis. We look and see which modules have trouble code. We found a few that were related to body control and the Can System so that’s where we started with our issue, but also verified that there was a four amp power draw from the battery when the key was shut off. So that’s huge, that’ll kill a battery pretty fast.

Mark: So a Can or a C-A-N System - what’s that?

Bernie: So a CANbus - it stands for Controlled Area Network and it’s a communications system used in vehicles that communicate between various modules. So your car, on this Mercedes there are probably at least ten to fifteen different modules, there are modules for body control, there’s modules for lights, there’s modules for the power door locks, the suspension system, the anti lock brakes, there are a number of modules and they all communicate with each other ver this, it’s like a pair of two wires and they communicate data signals back and forth. So it saves on an awful lot of wiring and allows a lot of complexity in the vehicle. Can is used in a variety of different vehicles, not just Mercedes unique. But they were early adopters, like they were for a lot of different types of technologies. So the problem with this system, some of the codes we were getting seemed to be related to the CANbus system, there were some communication errors going on.

Mark: So that sounds real similar to my previous life where I worked in processor design, so that sounds like it could be pretty complex.

Bernie: It is a very complex system, it requires a computer, the scan tool and a good quality one to work with the system. So once we have that it works pretty well but yeah, there’s a lot of complexity but we have the tools and the equipment to fix it. So yeah, that was the area where we started our diagnosis and looking at the CANbus system and the way the diagnostic procedure works with this is we disconnect different modules to see which one might be causing the system error, any particular module that can cause the other ones to misbehave so to speak, so it’s a matter of disconnection the modules and finding out where the error lies. Where these lights were staying on and where the excessive battery drain was.

Mark: Ok, that sounds like a lot of work. What did you do next?

Bernie: Well we disconnected everything and it got kind of frustrating because the power drain was still there and the lights were still remaining on, so we had basically ruled out any actual problem with the CANbus even though the codes were all from that area. And at this point, we were really at the point of disconnecting various components in the vehicle, unrelated items, and what we found was really interesting, something completely unrelated, nothing to give us any clue, but the radiator fan was actually causing the whole issue. The radiator fan is an electric fan, so there’s four wires, two like a power and a ground and a couple of communication, you know signal wires to turn the fan on and off. The fan wasn’t running, it wasn’t buzzing, it wasn’t doing anything but yet, once we unhooked that all the problems went away which is really, really bizarre.

Mark: Ok, that sounds a bit crazy, sounds like a do-it-yourself repair gone wrong.

Bernie: Well, yeah the do-it-yourself thing, so after we figured it out, we call the owner, because we looked at the fan and it looked quite new, so we thought this is interesting, looks like this part has been replaced, so we quizzed the owner and he said “yeah, you know like about a few months ago, in the summer, the radiator fan motor was dead so I replaced it myself”, he did a great job by the way, installed it nicely, and he’s like “come to think of if, that’s kind of when all the issues started happening”. So the fan motor was defective, so I’ll just actually share a couple of photos while we’re here. So there’s our Mercedes E320, a nice four door Mercedes sedan and this is the fan motor assembly. So the electrical connectors on the right hand side where my mouse is pointing, and yeah, that’s basically the unit.So that’s basically it. We installed a new fan motor, all the lights were off, battery drain down to about 30 milliamps I believe, perfectly normal and the car worked great.

Mark: So what’d we learn from this kind of experience?

Bernie: That’s a very good question that you asked and what we learned is, I mean we as technicians, we just follow a diagnostic procedure based on the best information we have. We got to start somewhere. There were codes for the CANbus and various systems so we followed that but what would of been really useful is for the owner to have said, “you know, one thing that I did do was I did change the radiator fan and the problems seemed to happen. People tend to forget that anything is relevant and it wouldn’t seem like it was relevant but if you have a vehicle, you have a problem that needs to be fixed and it’s you know, it’s good to think back of anything that may have happened recently, when does the issue occur, is it hot, cold, after running for 10 minutes, those kinds of bits of information are really really helpful for us to diagnose the vehicle. So often we get a car and it isn’t doing what the owner says and after we look at it for an hour, and you know, it costs money for the customer and then oh well, you know it did this and so if you can think of everything before your bring the vehicle in, write it down, really think hard, think twice that’ll save you some money for sure. And help us do the job for you.

Mark: So this brings up an obvious perhaps question, but was the fan actually running?

Bernie: No the fan wasn’t running.

Mark: Did the fan ever work? So it was a pretty obvious thing that this never, that the repair never really worked? Or it worked for a while…

Bernie: No I think the fan was working fine, it’s just as far as our diagnostic we never needed to even look at the fan because it was nothing. Normally if there’s a fan malfunction on a Mercedes, it’s pretty sophisticated, it’ll actually send a trouble code for a malfunction but it didn’t so yeah, the fan I believe was probably working fine if you warmed the engine up but we never even got to that point because we were chasing a power draw. And normally you know, if the fan was actually running while the key was off, well ok there’s a problem there, some kind of an electrical fault inside the unit. Again these things have like little control units inside, some little malfunction.

Mark: So in all honesty, would you have caught that if you had installed a bad fan motor?

Bernie: Well we would of, I think we would of. If we would of installed it, there would be no charge to the customer. So this is where sometimes I think you could save a lot of money by fixing stuff yourself but in the end, it cost this person a lot more money because he had to pay a lot of money to diagnose a problem that was result of a faulty part that they put in the vehicle. So had we installed that, yeah there’d be no extra charge. So bottom is it costs more money to have a car repaired in a shop than you could do it yourself but any good shop will back their work up, some don’t but you know, we do. So we care to make sure we install good quality parts and we do the job properly.

Mark: So there you go. Pawlik Automotive in Vancouver. If you need service on your vehicle and you want a warranty and quality repairs from people who really know what they’re doing, these are the guys to call in Vancouver, 604-327-7112 to book ahead, they’re always busy or check out their website We have years of these hangouts on there, tons of information of every make and model of car that we could possibly do so far. Thanks Bernie

Bernie: Thanks Mark.

About the author 

Bernie Pawlik

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