September 26

2011 Mercedes Benz GLK, ABS Brakes



Mark: Hi, it's Mark from Remarkable Speaking. I'm here with Bernie Pawlik, Pawlik Automotive in Vancouver. Vancouver's best auto service experience. 24 time winners best auto repair in Vancouver as voted by their customers. By you. And we appreciate you watching and listening. How you doing Bernie? 

Bernie: Doing very well today.

Mark: So we're gonna talk cars 2011 Mercedes-Benz GLK that had a break issue. What was going on with this vehicle? 

Bernie: Yeah. So there's some ABS brake problems with this vehicle. The warning light was on, on the dash. And when you apply the brake, even to the lower speed, there would be like kind of a vibration in the vehicle like the ABS brakes were activating when there was no need for them to activate. So that's what we were tasked to fix on this vehicle. 

Mark: So how do you test and diagnose to find out what's actually happening? 

Bernie: Well, there's a few things to look at. Of course, just verifying that the actual main brake system is in good shape, like the pads and rotors and calipers are all good, which we did. Seeing if there's any previous repairs done, and there had been. So the problem seemed to be emanating from the rear of the vehicle and the owner had been somewhere else and had the two rear ABS wheel speed sensors replaced, but that made no difference to the vehicle. 

So from there we connect a scan tool. We look for diagnostic trouble codes. And we look at data. We road test the vehicle and we can test sensors and then various things. So from that testing and a good visual inspection, we came up with two possibilities. One was that the ABS module was faulty based on how it was acting and the codes that were stored.

And also there was a possibility, which we figured the module was the first thing to replace. But a possibility also that the actual sensor rings at the back. So wheel speed sensor gets its signal from a ring, in the past they were like a toothed ring, you could see them, but they're a little more sophisticated these days. You can't even really see any teeth on them, but it's basically a ring that helps generate an electrical signal to the sensor, so the computer can tell is the vehicle slowing down, speeding up? What speed is it going? And it's pretty sophisticated.

So we could see that the sensors, the rings were hidden, but there's a lot of rust around that area. So we figured it's possible that there could have been a problem in that area. 

Mark: So where'd you start? 

Bernie: So we started with the module and we figured the module was the first place to start based on the symptoms that we were experiencing.

Mark: And what's involved with replacing testing, replacing the ABS module on the GLK? 

Bernie: So as far as parts, there's a couple different options. There's either new or used. They're a very expensive part new. There's basically a computer module, plus there's the actual module that does the ABS braking, it has solenoid valves that actuate at a very high speed.

So all the brake lines to each wheel all come out of this little box, which is generally located under the hood. And the master cylinder, there's two lines that come out of that. They go into the ABS module and then from there, the module sorts out how much braking to put to each wheel.

Now, if everything's normal, the ABS module doesn't do anything. It's just along for the ride. But if there's a problem, then it starts actuating. That's when you get that feel and that vibration. So we went with a used module based on cost. And fortunately this one there's no programming required. It's just a plug and play type of thing. A lot of times you have to reprogram them and do things. But in this case there wasn't anything. 

Mark: Makes for a simpler repair. Do you have some pictures? 

Bernie: It does. Yeah. I'll look at some pictures, but it does make for simpler repair and, you know, for many cars, modern cars, especially European, a lot of stuff needs to be programmed when you put it in. Anything electronic a lot of times it just won't communicate with the rest of the vehicle has to be programmed. Sometimes it's simple, but a lot of times it's much more complicated, so it can add a few hundred dollars to the repair bill. So always good when you don't have to do it. So there's our car, our 2011 GLK. And let's get down to looking at some bits and pieces.

2011 Mercedes Benz GLK, ABS Brakes

So there is the ABS module. This is the old one actually that we took out of the vehicle. But since we replaced it with the used one, it doesn't look much different, but couple things to look at here. You can see, this is an electrical connector. It's got four very large pins. These are where the powers and grounds go. There's a big motor here. And so this requires a lot of power to run this particular unit. These, all these little pins here, all for computer data and various solenoid activation. So this is for one view. There's a large motor and a pump inside this unit. Very high pressure unit. 

2011 Mercedes Benz GLK, ABS Brakes

These are the four break lines that go out to the wheels. There's a couple more, these are, I believe where, you know, coming outta the master cylinder. And then the solenoid pack would be over here where I'm kind of swirling my mouse pointer around. And then the sort of block in here has the actual valves. So these are much more compact than they used to be. At one time, these would be much more monstrous type of item with big, huge reservoirs and things they've managed to get 'em down to a pretty small size. So that's the ABS module piece.

2011 Mercedes Benz GLK, ABS Brakes

Mark: So once you replace the module, how did it run? Did you solve the issue? 

Bernie: Well, it worked much better. But there was still a problem. It actually reduced the ABS activation quite a bit, but it still was going on at a very under sort of, normal braking conditions. Before it was so severe before we changed the module that that severity was gone, but it still wasn't right. 

So we had to look a little further. As I said, we suspected there's possibly an issue. The area was still in the rear brakes. So we suspected probably the sensor rings because the sensors had been replaced and we actually verified and tested that they were okay. They were functioning okay. 

So we figured the next thing must be the actual sensor ring that was the issue. So that's where our testing went next. 

Mark: Okay. And what did you find? 

Bernie: Well, I'll just go right back to pictures because this is good stuff here. So there's our module again. 

2011 Mercedes Benz GLK, ABS Brakes
What we found is this. So this is the outer CV joint. That is the sensor ring right there, as you can see, and I should have taken a picture of the new axle. I didn't have a chance to, but if you can imagine a nice, shiny piece of metal with no crusty corrosion, this is pretty severe in a really bad shape. This is the sensor ring. We pulled it out and go, okay, this is severe, you know, this physically severely bad.
2011 Mercedes Benz GLK, ABS Brakes

This is another view of the axle. This is the outdoor section of the ring that are actually broken right off. So that's a sort of larger view of the axle, the CV joint, which is a flexible joint that connects the drive shaft is located inside here. This bolts up to the wheel side and the brake disk wheel hub. So the sensor where the arrow points, basically the ABS sensor sort of sits in here. And as the wheel turns, it generates a signal from that motion. So it wasn't able to do that. So that was our problem. 

2011 Mercedes Benz GLK, ABS Brakes

Mark: And these are the rear axles. Independent suspension, rear suspension on this vehicle? 

Bernie: Independent rear suspension. Yeah, the rear axles. All ABS systems work the same way. They all have a sensor in each wheel, with a little tooth wheel.

Mark: So how did it all work after you replaced the axles? 

Bernie: Excellent. Yeah, it worked really well. Worked like it was supposed to. No ABS activation, unless you really stomp the pedal down hard. And the vehicle was actually in a skid position.

Mark: So, is this a fairly rare repair where it's the axle rings that are at fault? This is an 11 year old vehicle? 

Bernie: Yeah, I mean, it's not that old of a vehicle, and based on that rust, I'd say this vehicle's probably been in some pretty salty, crusty road conditions. But it's not entirely rare to have ABS rings go bad. It's a definite issue on many vehicles.

Probably as common as sensors going bad. Maybe even more common because the sensor is generally, it's a very tiny copper winding located inside of plastic housing. So generally there, there are issues with them, but generally the sensors don't go bad cuz they're kind of sealed in plastic, but the rings are exposed to the environment pretty badly.

And there are a lot of vehicles where the rings actually crack because rust will expand on the axle and it'll actually split the ring open. And so that's a common problem on, I think there's a certain Ford vehicle, it's a little SUV, Ford Escape. Haven't seen one of those in a while, but that was a very common problem. It's almost like it wasn't much diagnosis needed, you drive the car around the block, you can feel it. And you go, I bet you that's the sensor ring. Of course we do need to verify it, but that's kind of an issue that happens. So not entirely rare. 

Mark: So it makes more sense to replace the whole shaft because that end is just so rusted. You can't just replace the ring? 

Bernie: Yeah, at least on a Mercedes, you can't buy the ring, but on the Ford Escape I mentioned you can buy the sensor rings. And I always like to do things most economically for our customers. So the first few times I did 'em I thought, Oh, great, we'll just get the ring. And what happens is, the rings actually crack, I'll just take the Ford, for example, the rings crack because they rust and then that expands the metal and then the ring snaps. But what happens is when you take the old ring off and you have to, of course remove all the old rust with the wire wheel. Once you do that the metals actually shrunk. So the ring doesn't fit on properly. 

So make a long story short while it seems more economical to buy a ring that only costs like 10 or 20 bucks versus an axle, which is a few hundred or sometimes a lot on an imported car, like a Mercedes. It doesn't work. Long and short of it is if the ring breaks or slips or gets corroded like this, the whole unit needs to be replaced.

Mark: So did you use an aftermarket axle shaft, if there is such a thing? Or did you have to use a Mercedes? 

Bernie: Yeah, we were actually able to get aftermarket shafts, which are a fraction of the price of the OEM Mercedes shafts. You know, truthfully, they're probably not quite as good but, you know, quite as good, meaning they may fail a little sooner in the life of the vehicle. But being a rear, they're not under the same strain as a front axle. But I mean, 99% of the axles we use in our shop are aftermarket. They last a long time and work really well. 

Mark: And they have a warranty as well. 

Bernie: Yeah, exactly. Generally two year, 40,000 K warranty. So it's pretty good. 

Mark: So, if you're looking for some service for your Mercedes-Benz, your GLK or whatever model of Merc you have in Vancouver, BC, Canada, the guys to see are Pawlik Automotive. You can reach them on their website, You can book online there. They'll call you they'll get ready for your appointment. Or you can actually phone them (604) 327-7112. You have to call. You have to book ahead because they're always busy. Pawlik Automotive. We really appreciate you watching and listening. Thank you. Thanks Bernie.

Bernie: Thank you, Mark. Thanks for watching.

About the author 

Bernie Pawlik

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