JMK123

I've read through several of the other Airmatic issues on this site and don't think I've seen the solution for mine yet. I'm hoping you guys can help me out. I would like to avoid going to a dealer if possible (1hr drive + all the other reasons we avoid dealers). Vehicle is a 2011 GL450.

Initial Symptoms:

• Air compressor was running more frequently than normal for a few weeks
• “Malfunction” error message displayed, and air compressor would not turn on anymore
• Over the course of a few days the rear suspension was riding noticeably lower

Work done already:

• Replaced air compressor with Arnott P3214 (along with new relay)
• Replaced rear air bags with Arnott A2596
• Replaced the air suspension solenoid / valve with Arnott VB3267. (looks like VB3823 is also offered for this model year, I'm not sure if it matters)

My mechanic was able to raise the suspension and do a “re-learning” procedure with his service tool, but the Malfunction error would persist and the air compressor would never kick on by itself. My mechanic did a re-learning procedure again and the suspension would appear to work normally for a few minutes, but then the Malfunction error would come back and again the air compressor will never turn itself on, so the suspension gradually lowers over time. My mechanic has also checked the electrical circuits and he says they are ok. We later found that the original compressor would still turn on when

When I was away on a trip I didn't drive the vehicle for 3+ weeks and the ride height stayed in its proper position so I don't think I have a leak anymore. If I push the "raise suspension" button I can use a jumper wire to directly power the two big 40A fuses (compressor power and relay), and that will raise the suspension to the off-road height. But if I wait too long after key-on, the airmatic malfunction message will appear and the solenoid block won't kick on.

It seems to me that mechanically everything is functioning normally but the system is not turning on so there seems to be some issue with the electrical system or the re-learning procedure to reset the system after repair. Any ideas?

Max Blast

Have you swapped out the relay?

eric_in_sd

Yeah, swap the relay. You got a new one with the compressor.

By the way, I think the 3214 is the Arnott Chinesium, not AMK. Brace yourself for possible early replacement.

JMK123

Yes I did swap the relay with the new one provided by Arnott

eric_in_sd

Why did you replace the valve block? Just to be on the safe side? The OEM valve block is very reliable, although they can fail due to over-running a pump in humid conditions. If there was no good reason to swap the valve block, try putting the old valve block back in.

Since you can raise the suspension, the system is actuating the valves okay. However, it is possible the pressure sensor in the new valve block is not functional. The system looks for rising pressure when the pump is running. Hook up a scan tool to see if there is a pressure reading.

If your mechanic has a bidirectional scan tool, such as Autel MP808 or STAR, instructions can be sent to the individual valves and the results monitored. The single dash Malfunction error message is not very informative; you need to get a little deeper, like with a MBII, to see the DTC involved. I tore my hair out with a Chinesium valve block that was completely unfunctional out of the box, because I could not believe the new valve block was bad.

My bet is you have a valve block with a faulty pressure sensor, and the system is rightly concluding that the results from it are "implausible".

By the way, the "re-learn" procedure has never been necessary on my 2007.

Since you seem like an inquisitive fellow, here is a crude physical schematic of the Airmatic system:

JMK123

Thanks for the response Eric. My mechanic thought the valve block must be the issue because at that point it was the only thing left we hadn't replaced. Let me explain the timeline a little:

1. I noticed that the compressor was running at startup more frequently and longer than normal, so there was some leak initially
2. Malfunction message, compressor stopped turning on
3. Replaced rear air bags, compressor, and relay
   1. Note - my mechanic tested the compressor with 12V and it does turn on, so maybe it wasn't bad
4. Mechanic can raise suspension manually by providing 12V to needed circuits, tried some relearning procedure that didn't work
5. Replaced factory valve block with new VB3267 because that seemed to be the last remaining item
6. Still not raising, scan tool showed about 50 stored diagnostic codes, below are the ones related to Airmatic. I'm not sure if they were ever cleared so these might have been stored before any of the repairs / part replacements
   1. 5507 - Suspension Strut is Implausible;
   2. 5400 "Check component F58kG (air suspension compressor).";
   3. 5508 "The Pressure Line System Leaks."
   4. 5539 "One Or More Signals Sent From Control Unit N51 (AIRmatic With ADS Control Module) Via The CAN Bus Is Implausible"
7. Mechanic reached out to the dealer for guidance, the dealer provided a different re-learning procedure. I don't know the details, it involved some sequence of pushing buttons on the dash
8. Mechanic says that after the re-learning procedure the vehicle will kick on the compressor by itself for a few minutes but then trip the "malfunction" message after which it won't turn on the compressor any more or raise the suspension.
   1. I think it does lower itself from off-road mode to regular mode after exceeding a speed like 35mph, and it does seem to lower further for highway mode at higher speeds, so then I'm stuck with somewhat lower ride height.

Based on your response I'll try the following steps next:

1. Check for pressure reading
2. Try sending signal to individual valves with bi-directional scan tool (any particular result to check for? Just proper function that I can raise/lower each corner independently?)
3. Troubleshoot relay by testing voltage across terminals (saw this in another thread, it's easy to do and seems like a bad relay could explain my issue)
4. Somehow check which DTCs are currently active, might need to clear the stored DTCs and see what trips again
5. Swap back to the original valve block

I will plan to go to my mechanic on Monday afternoon to try some of these steps. Anything else I should add? Thanks for sending the diagram, it is helpful to visualize how the system works

Max Blast

Check that your level sensors havent been overtravelled and are flipped. They will still give a readout like this but it will be implausible as the suspension flexes.

What about your front air springs, do they leak?

eric_in_sd

I did not realize you changed the valve block after finding no relief changing the compressor. In the future, try to sort everything chronologically; I learned this from reviewing a dealer mechanic's notes. Result - action - result and so on. Since you changed the valve block after changing other stuff, the valve block is much less likely to be the culprit.

You can check the pressure sensor with a bidirectional tool. Just query the pressure at one of the springs or the reservoir. The system will (audibly) click open the valve to that item, and display the pressure.

Also, the fact you have ADS is important. It may desire - but probably not need - a re-learn. My 07 has no ADS, thank heaven.

Definitely clear the errors and see what is current. The last of the errors is worrisome, and indicates you have a failed control module.

The relay is probably not bad if you can get the pump to work sometimes with the relay; but it is easy to swap with other relays, or even the one you took out. I have accumulated spare relays because I have changed pumps several times and never replaced them.

Here is the order I would do things:

1. Clear the stored DTCs and see what trips again (get used to doing this; I have worn a flat spot on my index finger)
2. Check for pressure reading by sending signal to individual valves with bi-directional scan tool (this will also tell you whether the control module is sending signals!)

Max Blast

@eric_in_sd , where is it stated that OP has ADS? Late run X164 450s usually don’t.

that complicates things, if so.

eric_in_sd

> 5539 "One Or More Signals Sent From Control Unit N51 (AIRmatic With ADS Control Module)

Max Blast

Yeah, I suspect most of these codes are garbage.
Troubleshooting airmatic is a pressures and sounds kind of thing and the codes don’t really do much… They just tell you in the vicinity to hook your peepers and plant your ears.

Not aware of any late model X164 that had this option, and that the signal is implausible from the ADS module could mean that the ADS isn’t there.

Also, I have a public service announcement because today I learned: the car will not lower itself with any door open. So for those of your troubleshooting saying that your cars are stuck in high mode, be sure that all doors are closed.

JMK123

Thanks, I will try that

eric_in_sd

lol remember my intake valve carbon problem? I stared at DTCs for hours, but it was not until I put a borescope in the combustion chamber that I figured out what the issue was. Getting info from the computers is like getting directions to the party from a drunk chick.

The doctor doesn't like it any more than you, but to diagnose your prostate the best method is to stick his finger up ... never mind.

@JMK123 Confirm that you have ADS.

JMK123

I don’t think I have ADS. No sport/comfort setting. Here’s a picture of my front left shock.

Max Blast

You do not have ADS.

Max Blast

OP, have you swap back to original valve block?

JMK123

Not yet - planning to do next steps on Monday when my mechanic is available.

eric_in_sd

Note the valve block was replaced in response to the problem, not as part of a parts dump.

eric_in_sd

Get fresh DTCs before doing anything else.

Then try sending instructions to the valves, etc., to see what responds and what doesn't. You may have to clear DTCs before doing this; the module being probed may shut off in response to the error condition.

JMK123

I was able to do some troubleshooting with my mechanic last week, it's still a bit of a puzzle. Here's what I found:

• Stored DTCs were as previously posted:
  • 5507 - "Suspension Strut is Implausible.";
  • 5400 "Check component F58kG (air suspension compressor).";
  • 5508 "The Pressure Line System Leaks."
  • 5539 "One Or More Signals Sent From Control Unit N51 (AIRmatic With ADS Control Module) Via The CAN Bus Is Implausible"
• We cleared DTCs, keyed off, and re-started the engine, and these DTCs logged again:
  • 5507 - Suspension Strut is Implausible (Stored)
  • 5400 "Check component F58kG (air suspension compressor). (Current and stored)
  • 5508 "The Pressure Line System Leaks. (Stored)
  • 5503 Recovery Time During Filling Of Central Reservoir Is Too Long. (Stored)
  • Additional non-Airmatic faults are also logged, I posted that in a picture below
• Airmatic Pressure Sensor read 0.55 bar (this looks like a reasonable reading to me - pressure sensor seems to be working?)
• We were unable to read pressure at any other location other than listed above, when trying to read pressure at one of the struts or the reservoir we would get an error message. I wasn't familiar with the error so I can't say if it was a problem with the scanner or if the signal wasn't going through to open the necessary valves
• Voltage query showed a result of Terminal 30 = 14.2 V and Terminal 87 = "ON"
  • Does this indicate a properly functioning relay? Or should I break out the multimeter to verify? It has the new relay from Arnott right now, I still have the old one.

If a re-learning procedure is not required, it seems there must be an electrical (either power or signal) issue going on here. I've already replaced the valve block to no effect, and I've observed that the suspension holds its height indefinitely when parked, but lowers itself when driving, so I think I can rule out the valve block. So I'd be thinking I may need to go around with a multimeter to check where a signal is getting dropped? Is there a more efficient way to troubleshoot that deeper? Any other ideas? Thanks for the help!

DTCs logged again after clearing:

• 
  System Fault Codes after clearing
  

eric_in_sd

If it would not send signals to the valves, then the airmatic control module is probably glitchy. You should be able to take a pressure reading of any one pressure component by clicking open the appropriate valve and reading the sensor. This is assuming you (your mechanic) is using a respectable bidirectional diagnostic computer.

The other possibility, looking at the other faults, is that you have generalized faults in the computer system. This could be water penetration damaging the front SAM (see last fault). Or it could be you have a marginal / dying battery &/or alternator (unlikely given 14.2V reading).

The half bar (that's 8 psi) pressure is reasonable with no valves open; the pressure in the line has simply bled down. If you were to watch that pressure with the pump turned on but no valves actuated, it would quickly rise to the maximum pressure the pump is capable of - like 20 bar. Needless to say, this is not an experiment you want to run for long!

Max Blast

Eight psi is much too low. That’s only half a bar and the reservoir pressure should be 16.

I don’t know where this measurement was taken. But again you need to retrace your steps and I would start with the valve body being suspect since you replaced OEM valve body with possibly Chineseium.

you simply have too much going on here, but if I’m reading the codes and these are correct, it is that your compressor isn’t putting out the pressure it is required to do, and as a result, the level sensor output doesn’t make any sense and it triggers and implausible code. The problem is air compressor is not putting out enough pressure to the Reservoir. Ask yourself why. If you have a proper scan tool, you can run the compressor output test that measures the pressure from the compressor to the valve block. Then you can measure the pressures in individual lines as well as the pressure in the central Reservoir, the pressure in the central Reservoir should be 16 bar.

eric_in_sd

Recall he said he was not able to measure individual pressures. Thus the pressure reading is just on the manifold with all valves closed. It is a meaningless number without valves opened.

EmilyMB

Have you checked the fuse block circuit board.
It may have weak solder joints , etc….
Don’t assume anything, just try to eliminate every thing that relates to the problem
Merc has many weird problems.





Pictures from google.