I've got a Mercedes gl 450, 2008 which has so many problems I'm about to convince my dad to just buy a newer model, or different brand. My problem today is the airmatic suspension system, and I don't even know what to tell you because I don't know where to start. Firstly, the button to raise the suspension is out of service. the light wont even FLASH. as soon as the car is on, we get a suspension warning on the dash. We tested the relay, 2 fuses found in the back(trunk), the compressor fuse and relay, and nothing worked. We even replaced the pump today and it still doesn't work. We can start the pump manually from the relay insert, but I don't think it’s actually pumping the suspension up. The rear suspension could be broken, I don't seen signs of it, but I know the front suspensions are fine because my dad recently replaced them. Any and all help will be appreciated, as we already have too many missing/broken functions in this vehicle.
Edit: we just found a bad fuse we’re gonna replace it and see what happens.
Edit 2: It still does not work. (Fuse 32 in the rear)
Edit 3: Few hours later we are realizing every time we put a new fuse in, it breaks as soon as it touches the connections. You can hear the pump turn on for a second before turning off, and breaking the fuse.

 

So what was it doing before you replaced the compressor?

 

It was working fine at first, then we started used it more often, then it stopped working. After a while we noticed the compressor would be making noise while the car was off, so my dad told me to leave the compressor fuse out for a while. Now after leaving it back in, it wouldn’t work. We checked relays, fuses and the old pump, they all work.

 

I'm not entirely clear on the sequence of events, but let's pare the system back a little bit and take it step-by-step. If I understand correctly, you can put a new fuse in the circuit that feeds the AIRMATIC control unit, the compressor starts running momentarily, and then the fuse blows almost immediately, right? First thing to verify is that you're using the correct amperage fuse of course - I think it's a 15 if I'm reading the diagram correctly - but I'm sure you've already checked to make sure. It looks like the control unit is fed from that fuse 32 and the motor itself is fed from fuse 108 (40 amps) under the hood. So if the motor was pulling too much amperage, it should be blowing 108. I might start looking at the control unit and its wiring to see if it is shorting out. For example, with the #32 fuse removed and the control module unplugged, pin 47 on the AIRMATIC control connector should not have any continuity to either battery terminal. If there is continuity there, then you've got some sort of break in the wiring harness for the power feed for the module and it's shorting out and blowing the fuse. If that's clean, then it could be a different wire shorting out or it could be the control module itself with an internal short. Try unplugging the compressor connector and replacing fuse 32. I'd also check the wiring to the compressor - with the fuses out and the connectors for the compressor and the control module unplugged I think you should only see continuity to ground on the brown wire at the compressor. If those wires don't have a short and the fuse still blows right away with the compressor unplugged, then you've got a bad compressor. If that fuse still blows right away, even with the compressor unplugged, then your short is in the module itself or in something that is connected to the module feeding back to it. But if you're blowing a fuse then you've got a short somewhere in the system.

I also suspect that if you had a copy of DAS and an OpenPort 2.0 there might be some better step-by-step troubleshooting capabilities. I've found it to be pretty decent about telling you what sorts of voltages and whatnot to look for in which places. I'm just pulling up the wiring diagram and trying to follow the flow of current to narrow it down a little.

 

So we just tried unplugging the compressor with the fuse in front out(108), and put in the one in the trunk(32), and the compressor wouldn't go on after putting the fuse back in (32, and 108), and the button still wouldn't work. What did we do wrong, also im a little confused on the instructions Where and how do i check the control unit? Where is Pin 47? What is DAS or OpenPort 2.0? We don't have any Mercedes specific OCD scanners. Additionally, fuse 108 still isn't broken.

 

If your compressor runs but doesn't inflate the bags, I'd look at the valve block. Maybe the wires or something internally is messed

 

Okay, let's back up a little bit, then.

DAS is the software from M-B that will speak to all the various computers that they've sprinkled throughout the chassis and allow you to read their diagnostic codes and perform testing procedures. An OpenPort 2.0 is a hardware dongle that will connect to the ODBII port on one end and a USB cable on the other end. It will translate between your laptop and the car so that you can communicate with some of the manufacturer's protocols that your basic OBDII scanner can't. They're often sold as being specific to Toyota from what I can find because I guess they come with some software that replicates whatever Toyota's diagnostic software is, but I don't really know much about that. If you're going to be DIYing one of these overgermanengineered beasts, you're going to need this in your toolbox, otherwise you'll be left guessing a whole bunch. You can get an OpenPort 2.0 from Amazon for under a hundo and if you look about on internet auction sites, you can find copies of Xentry/DAS available. It's also good if you can have a copy of WIS as well as that's the comprehensive factory service manual, including wiring diagrams. You might be able to get similar data from AllData - I've had really good luck with them for other makes, but since I have a copy of WIS, I've never tried them for MB.

At any rate, speaking of guessing a whole bunch, that's what we're doing here. Looking at the wiring diagram, the fuse that your AIRMATIC system is blowing is not the one for the compressor - fuse 108 under the hood - it's the one that appears to be for the control module. When a fuse blows it tells us only one thing: Something is drawing more amperage than that fuse can support. Okay, so what causes something to start drawing too many amps? Typically that's going to be either something like a motor that's trying to perform more work than expected, or a short circuit. We can get a short circuit from a chafed wire, fluid intrusion in to the harness, failed components on a circuit board, or some sort of breakage inside a sensor or module. What we're trying to do right now is locate the source of the short circuit.

Because fuse 32 is the one that keeps blowing, we can assume that the over-draw is coming from the module side of the system. That helps to narrow things down. If Fuse 108 was the one blowing, then we could assume that the fault was with the compressor in some fashion.

By removing fuse 108 and keeping the others, we're cutting power to the compressor itself but allowing the AIRMATIC module to come on-line. What we want to see is if that causes the fuse to blow when the module powers up. I'm making an assumption that the AIRMATIC module will come on-line and attempt to fire the compressor. That might be a faulty assumption, of course. I don't know if there is some checking of the compressor that's going on that would prevent the module from powering up at all, but my guess is that if anything is checking the status of the compressor it would be the AIRMATIC module itself. So with the compressor de-powered, if the system doesn't blow the #32 fuse right away, we probably don't have a short circuit between the rear fusebox and the AIRMATIC module. If, however, the fuse still blows, then it's a safe bet that the problem has absolutely nothing to do with the wiring between the fusebox and the compressor. We've depowered that by removing the fuse, so there shouldn't be an opportunity for it to short to ground.

If the #32 fuse blows, even with the compressor disconnected, I would want to check the wiring to the AIRMATIC module as well as the module itself. I'm not entirely sure where that module is physically located - I'm away from my instance of WIS right now - but if you can determine its location, the wiring diagram says that pin 47 is the +12v feed that comes from the fuse box. By removing that fuse, you should now effectively have a wire that is disconnected at both ends and is no longer capable of completing any circuit. By checking continuity between pin 47 on that connector and any ground on the car, we're verifying that there is not a short to ground on the feed wire. If, with the fuse removed, that pin has continuity to ground, then that means the wire is broken somewhere in the harness, there's something broken loose in the fuse box, or there is some sort of fluid intrusion somewhere. If, however, that is showing an open loop to both the negative and positive battery terminals, then we can assume that the power feed to the module is intact and not the cause of the fuse blowing.

If the module doesn't blow its fuse with the compressor de-powered, then one of two things are happening: (1) That module isn't even getting powered up if the compressor doesn't have power (which I think is unlikely) or (2) the problem is somehow with the compressor or the wiring to the compressor.

If that module does blow its fuse, however, then the problem is either with the wiring to the module, the module itself, or the compressor or the wiring to the compressor. Maybe a sensor, but those can usually short out without taking the fuse.

If the module blows its fuse and there is no continuity between that wire and ground, then I would suspect the module is faulty or the output to the compressor is shorted somewhere. That's why I'd recommend unplugging the connector at the compressor so we can take the compressor completely out of the equation. With just the fuse removed, there could still be some path to ground. If we pull the connector, though, and the fuse still pops we know for a fact that the compressor has absolutely nothing to do with it.

This is actually where DAS can be pretty helpful. It will pull the code from the vehicle and tell you, probably, that it can't communicate with the module. Now, we know that's because the module is blowing a fuse and getting de-powered but it will give you some troubleshooting steps as far as checking for voltages in specific places and things like that.

 

The module was infact faulty. Now we have replaced it, the button works, the pump works, but that's where the fun ends. When the pump kicks in, the car automatically stops. And this can be avoided by simply removing #32. The previous module was faulty because it was drowned in coolant? I don't know how that got there, and something burnt in the middle of the module.

 

I’m not entirely clear on what’s going on here can you restate the problem using chronological bullet points and a lot less words please?

I’m not trying to be facetious or a Richard. I just can’t make sense of this.

 

Air suspension go die
New pump doesn’t solve problem
fuse 32 is the rear blowes immediately after putting a new one in
here we are after replacing the module, the module won’t blow the fuse instantly, but the pump turns on as soon as the car does, turning off the car.

 

Read through this similar thread

https://mbworld.org/forums/gl-class-...tting-off.html

 

the solution in this thread was to soulder? Not everyone has those skills. It doesn’t even specify which board they souldered on.

 

A shoulder repair isn't that hard, although you are right, it is not what you want to attempt on the shoulder of the road, but sometimes it is a burden we must shoulder.

 

right, that was the cheaper repair to what otherwise would be a buying a new or non-good used module, and having it coded to your car by an independent or a dealer with a Mb
star system. Just reading the two I think you’re looking at the same symptoms.

 

we already got a replacement module. And this isn’t he first time I’ve heard star system. We’ve already had several problems with his car and our best response is: “Star reinitialize.”

 

Just for everyone’s general interest ; MB Star/ DAS / Xentry is three different names for the MB proprietary communication and repair system used to diagnose all modern MBs from at least 2002-2015.

There are very few over the counter Obd2 scan tools that can hook into the MB system architecture and give you actionable Information, which is why this forum generally recommends owners who are in it for the long haul to obtain an MB compatible scan tool.

For your application it will tell you what the level sensors on each wheel are reading, as well as pressure in each line and the central reservoir, and most importantly be able to run function tests on each component in the airmatic system. This could eliminate a lot of variables and find your true issue.

all of the functionality above is to be used after a thorough leak check of the system, which is best done with ears and eyes. Sounds like you’ve done that already so I would recommend your look for a good scan tool next.

 

bha, we have to shoulder the fact that your response was correct.

 

Last post stands head and shoulders above all else said here.

 

Has anyone hooked up two systems to each other to see if Star Wars results?

 

Electrical gremlins can be so difficult to chase down! I have only the vaguest understanding of how these things work (and I'm currently (ha! get it?) mired in tracing an electrical issue with a different car), but I'll try to explain the best I can.

Basically what you have happening right now is when the compressor kicks on, it's pulling a significant amount of current to get the motor started. To be fair, the normal running amperage is high as well, but motors typically have a higher in-rush draw and the older a motor gets - especially a compressor for some reason - the more draw they put on the circuit. When that compressor is kicking on, it needs to pull that current from somewhere and if it finds a significant amount of resistance in the path, it will need to pull ever more current to overcome that resistance. Resistance translates to heat and the heat will degrade the connection which results in more resistance which results in more heat and so on. Eventually that connection will be heated up to the point that the conductor melts. This is how a fuse works - the conductor inside the fuse is rated to pass a certain amount of current without resistance. Once the draw on that conductor goes over that value, the conductor will heat up and break to prevent any other component in the system from heating up and catching on fire. If the only path to complete that circuit is in whatever connection has failed, then the devices on that circuit will stop working but everything else will be fine. If, however, there are other paths to complete that circuit, the current will attempt to traverse those other paths. That could result in cutting power to devices another circuit because there's now a path to ground that doesn't involve going through those devices. It can also - and this is a technical term - "confuse" electronic modules that are expecting certain voltages or signals and have just become a path in a circuit that was heretofore unknown to them or their designers.

After reading that other thread, it appears that what others have seen is that there is a trace on the circuit board for the fuse box that was designed in such a way that it will degrade and burn up at current levels below what the fuses are designed to blow at. A tracing is basically a wire that has been embedded in the board itself. When the pump starts to pull too much amperage, that tracing heats up and eventually melts. By removing that board from the fuse box, others have been able to examine it to find the burned up tracing and have been able to either repair the missing trace with solder or they have bypassed the trace entirely by soldering an appropriately-sized jumper wire between the two end-points of the tracing. By appropriately-sized, I mean a wire that is of thick enough gauge to support the current. Keep in mind that a thicker wire will support more current and have a smaller "gauge" number. That is to say that a 12 AWG wire is physically larger than a 20 AWG wire and the 12 AWG can support more current over longer distances.

If you were to remove that board from the fuse box - and it appears that you can do so by releasing some tabs in the body of the box via some slots AFTER DISCONNECTING BOTH BATTERIES so you don't do any surprise welding - you could visually examine it to see if there are any breaks in the traces. Assuming that the wiring diagram is detailed enough (and it probably is, but I haven't chased that down personally), you could also use a multimeter to check the resistance between all the various terminals to see if there are any terminals that should be connected to each other that are now showing as either "open loop" or any resistance. If you find a bad circuit, you could either replace the whole board with a new or used one - and it sounds like that is not terribly expensive and doesn't require any module coding - or you could use a soldering iron and some solder to make the repair yourself. The tools and supplies are not expensive, and about 15 minutes with YouTube will get you to the point that you can do the repair.

Hope that helps!

 

 

The most eloquent post thus far.

My friend, and I mean that literally, you have to understand you are receiving free advice from volunteers. Some is worth about the price you pay for it, and others, priceless.

You need to enter all this with an attitude that you have to figure things out for yourself, and sometimes you, and your advisors, will be wrong. Case in point: I shelled out for a throttle body and ECU to fix a cylinder carbon issue. Neither fixed it, but I do not blame those who gave me wrong suggestions.

You have been given input, and from the looks of the responses in this thread, members are getting tired of your complaining. Before you completely ruin things, I advise you take what you have been told and formulate your action plan - which may include giving up and turning the vehicle over to someone else to fix. There's no shame in that.

 

Don’t get me wrong I appreciated all help in this thread. Done things were troubleshooting methods I already tried, didn’t understand, or couldn’t do, like do that STAR thing. We ended up finding am someone who could solder that connection together, fixing the problem. Now we just have to fix some sort of leveling issue, which I’m sure I can find help with in another thread.