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I have read posts where people have quantified the output pressure of the suspension compressor. I had the tech run the VAGCOM performance procedure where the functions of the suspension are activated with the VAGCOM. He said he did not see any reading telling how many BAR pressure was being produced. What does he need to do differently in order to test that output ? The pump makes a lot of noise and it has run so much that I bought a re-build kit for it but I would like to quantify the before and after performance.
And is the pump controlled by the Valve Block or another control module ? I have two new OEM front struts and no leaks, which is to say, the car does not drop when placed in 'Jack Mode' over night. Yet the pump runs almost constantly; shutting off with a burst of air released every time I brake to a stop. And yes I have replaced the relay. VAGCOM showed no incidents of thermal shutdown of the compressor.
I really need to solve this riddle !! I am tired of listening to the pump and hearing that 'semi-trailer-air-brake-sound' every time I come to a stop. I am going to replace the valve block because the VAGCOM says 'Signal from Level Control Pressure Sensor (G291) has an intermittent Implausible signal' and that sensor is in the valve block. But I need to know if there is another control module involved in the system.
The pump is controlled by the suspension control module, part # 4E0 907 553 F.
Address 34: Level Control Labels: 4E0-910-553.lbl
Part No SW: 4E0 910 553 H HW: 4E0 907 553 F
Component: LUFTFDR.-CDC H06 4480
Coding: 0011210
Shop #: WSC 02313 785 00200
VCID: 285BFC93E7D7
And yes there is an output bar reading in the Ross-Tech software, will have to search as it was just posted on not to long ago, I will take a look.
Any idea as to the physical location of that module ? I see on eBay there are revision letters 'E' through 'J'.....any idea which revision your W12 (and therefore mine) has ?
I think the question you should ask is why the pump is on constantly? My pump never pump while driving. As I read and understand the system, when you set the level with MMI, nothing will need to change until you hit 70mph, which means the level is set at desired selection. If nothing leaks as you confirmed by the jack mode tests, then the level should be good and the pump should be resting and off. What else can cause the pump to turn on? The suspension moves up and down, the level sensors may get stuck or loose, resulted in false level, the pump turns on. When you stop the car, the level sensors is at rest, the correct level read, too high due to over pumping, since your system is good, it releases the air to lower the over inflated suspension. Again, it's my diagnostics, you may listen or start replacing more good parts and kill the system with the vcds. The pump never have to work so hard to maintain a desired pressure in a good system.
Cheers,
Louis
I think the question you should ask is why the pump is on constantly? My pump never pump while driving. As I read and understand the system, when you set the level with MMI, nothing will need to change until you hit 70mph, which means the level is set at desired selection. If nothing leaks as you confirmed by the jack mode tests, then the level should be good and the pump should be resting and off. What else can cause the pump to turn on? The suspension moves up and down, the level sensors may get stuck or loose, resulted in false level, the pump turns on. When you stop the car, the level sensors is at rest, the correct level read, too high due to over pumping, since your system is good, it releases the air to lower the over inflated suspension. Again, it's my diagnostics, you may listen or start replacing more good parts and kill the system with the vcds. The pump never have to work so hard to maintain a desired pressure in a good system.
Cheers,
Louis
'good system' would not have a compressor running; system with a bad module might. I am hoping it is that module. If not, then I will have to have you deduce the cause for me.
You have to go through all the outputs tests of the level control module, which are performed sequentially. The accumulator test is the last one in the sequence and it runs the compressor in an attempt to pressurize the accumulator up to its operating pressure of 16 bars/232psi. I’m not sure what the “test passed” pressure threshold is, but mine is only able to get up to 8.5 bars and it tells me “test failed”. I have no leaks but know the compressor is worn as the car is slow to change levels, as it’s only able to deliver about 50% of its design spec pressure. I also get occasional implausible pressure sensor warnings. This is because the compressor isn’t able to deliver the pressure that the systems algorithms are expecting to see, so it logs an error. I have no suspension error lights and everything works fine, just need to get around to doing the rebuild.
Regards to the compressor running for longer when it’s worn, despite system leaks not being present, I’d have thought it pretty obvious as to why? The compressor can’t deliver as much pressurized air as it’s designed to, so it has to run for longer to get up to whatever pressure it needs to. The pressure it’s trying to achieve is whatever is needed to maintain the ride height for the selected suspension mode. Once it’s done that, it then pumps up the accumulator. It will run the compressor until the accumulator reaches 16 bars, or the maximum compressor runtime times out, or the compressor overheats. Obviously a worn compressor can’t deliver 16 bars, so it times out at the maximum pressure it’s able to deliver. An overheating compressor is due to an already hot compressor being commanded to cycle on too often due to either a leak, or very poor compressor performance and heavy loads in the vehicle requiring higher pressure in the airbags to maintain ride height.
A failed valve block or controller will generally show very different symptoms, so don’t just throw parts at it without tackling the known wear items first.
So Dave, does your weak compressor run almost ALL the time like mine does. It doesnt seem by logic that it runs that much because it is low output (though I expect it is now after all that running and thats why I want to know how to tell the guy to check performance) and needs to run all the time to keep the accumulator filled and the car to height...if that were the case, would not the compressor be running all the while the car is turned off ? I mean the car still has to remain at designated height and when the accumulator gets depleted doing the job, then the compressor kicks in. The compressor does not run when car is 'off' because this car, seemingly, has no leak and therefore is not creating a need for air.
So if there is no leak there would be no leak i.e. actual need for air when under way either would there ? But it would seem that something in the system THINKS there is a need for air and so tells the compressor to run. What do you think of that theory ? And what component could cause the system to think that and run the compressor to fill the 'need' ?? And why turn off every time I come to a stop; though I do hear the burst of air sometimes going down the road as well.
If I do the labor to get me to the pump for a rebuild (if I can quantify a sub-par out put) then I would probably change out the valve block with a used one just because I am there in case it does have some bearing on the problem. What say you ?
Looking at the air suspension diagram below. There are 2 things that can cause the compressor to turn on constantly while driving: False pressure reporting by G291(11) in the Valve Block, leaking compressor exhaust valve(5). The accumulator(12) pressure should be @ 16 bar. When the accumulator has less than 16 bar, valve 10 will open to fill it up, I assume when the everything is good and air tight, the line to G291 should be at 16 bar also. When the line is less than 16 bar, reported by the G291(11), the compressor will turn on. So, if G291 is good, the only way the pressure gets lower than 16 bar is if it's leaking through exhaust valve 5. Since your system releases air when you stop (over inflated pressure), I believe the line has 16 bar but the pressure reporting is wrong the whole time. About the level sensors, I believe they're only used for self leveling and heights warning and not for the compressor to activate. The compressor ON/OFF is totally dependent upon the pressure inside the VALVE BLOCK.
The compressor can’t/won’t run if the car is off. The auto level whilst it’s “asleep” uses air from the accumulator. If there is insufficient pressure in the accumulator, the car will eventually sink down.
In its simplest form, all the compressor does is try to pump the system up to the required pressure to maintain the required level. It will only shut off once the ride height is reached, and the accumulator is pressurized, or it overheats.
If your compressor is literally running ALL the time and never shutting off, then the root cause is almost certainly a dynamic airbag leak. Just because it holds height whilst stationary in Jack mode, doesn’t 100% mean that when in motion there isnt a leak in an airbag that opens and closes as the suspension goes up and down.
I just browsed Level Control Measuring Blocks in VCDS. There are something like a dozen groups. I also ran the tests. ( Tests seemed good, but I do have a leaky left front strut)
OK - you can look at the status of the Compressor RELAY = ON/OFF.
Compressor temperature (Mine was 25DegC and up to 38 DegC after I lifted the car, ambient is 8 DegC)
There is a DRAIN VALVE OPEN/Closed.
Accumulator Valve Open/Closed
And various pressure readings - at each corner plus system pressure (?)
What caught my eye for this discussion is the drain valve. I would check that status, monitor the compressor status and temperature. If the drain valve is somehow compromised then the compressor will stay on unable to make pressure. Could also explain the air wooosh sound.
01-19-2018, 04:06 PM
how to get suspension compressor output reading ?
