Mika Riikonen

Had the car in a MOT test.

While there were three struts with a damping efficiency of 71...77%, the rear-right strut only showed 39% efficiency.

- is there anything 'serviceable' a home mechanic can do to overhaul a rear strut?
- if a new strut is installed, does it require any 'resetting/calibration' using an MB specific scan tool?
- is replacement a PITA for a home mechanic?

Maj. Dundee

The answer is yes and no but you should always have the codes read in the Airmatic Module.

texterted

Well, that's for the airbag Major!
There's nothing you can do with the damper unit it's integral to the strut assy. unfortunately.
But the strut is an easy job, two bolts on the inside, near the rear sam cavity. You may get enough access by prying the liner away but watch the wiring!

When you secure the bottom nut and bolt, do it with the weight of the car on the wheel, or use a jack or something. You don't want that bushing twisted.

However, check the electrical connections first. It'd be a shame to change it due to crusty contacts. The struts do fail tho. In fact I had one damper unit detach from a rear strut on mine!

Maj. Dundee

Tex, my mistake and will edit my post with correct procedures.

Maj. Dundee

Is this what he is referring to?

texterted

No, an easier description would be the "shock absorber".

Maj. Dundee

But he has Airmatic.

texterted

Of course but he means the other part of the suspension that isn't the airbag!

Maj. Dundee

Thanks Ted, got it.

Mika Riikonen

Sorry for the strut/shock confusion - my bad!

I did not know until now that the air spring and shock absorber are separate units...Thought they were combined...

- there appear to be shocks with and without 'electronic damping control'. Can I see which one I have just by removing the wheel, or is there a good VIN decoder which could tell it right away?
- is the rear differential really sturdy enough as a jacking point, so that I could put jack stands under the sill jacking points?

Thanks for service instructions and other advice!

Maj. Dundee

Here is a vin decoder. https://www.vindecoderz.com/EN/Mercedes-Benz

Jack up each side and place jack stands.

Mika Riikonen

Well, my wife called and told that the suspension is now rock-hard.

Googled the symptoms and found that the Airmatic control unit is in limp mode and shocks have thereby been set to their hardest setting. It was suggested that the control unit should be calibrated or the issue might stem from a bad connector to the shock, a faulty acceleration sensor on the shock or a fault in the ESP system.... What a drag!

I'll take the car to MB and have them read DTC's and perform calibration, to start with.

Mika Riikonen

I finally got the car for a test drive and scanned it using a Delphi 150E scanner (Chinese piece of s*** replica).

- from the outside, the car sits low. The wheels, however, are not sunken into the wheel wells but you can fit two fingers sideways between the tyre and fender arc in the front and three fingers in the rear. There is no difference between left/right, and Delphi shows ride heights -106 mm (front) and -110 mm (rear). When watching images of S or E models with wheels deeply into the wheel wells, I am not sure if the chassis is resting on the emergency rubber pads or not.

- when starting up the engine, there is no alarm on display. The Airmatic symbol with 'Malfunction' text comes while driving - the appearing is not clearly related to driven distance, time or speed. When the malf symbol appears, Tempomat cannot any longer be adjusted or engaged and the 'Parking' chime does not sound when engaging P.
- when driving, the suspension is very stiff on compression and very loose on rebound. So, very harsh on any bumps and then remains rocking up/down. Engine power is all there. There is never a "go to workshop" alarm.

- I checked the fuse and replaced the relay - to no avail

- Hooking up the Delphi was quite problematic, with plenty of connection problems into and within various control units. Therefore, I cannot tell whether certain test function issues arise from the Delphi or the control units themselves

- the following DTC's were in the Airmatic unit:

5505 - Recovery times during filling of air suspension strut is too long. - Intermittent
5503 - Recovery time during filling of central pressure reservoir is too long - Intermittent
5508 - Hydraulic Pressure Unit Leakage - Intermittent

- having erased them and done a test drive, 5508 - Hydraulic Pressure Unit Leakage - Intermittent, had reappeared

-Here are various data derived from the CU:

- Ride heights: LF (4.3V, -106mm); RF (0.7V, -106mm); LR (0.9V, -110mm); RR (4.2V, -110mm)
- Pressure sensor: 0.41 Bar, 0.45V
- Compressor locked: NO
- Terminal 87: ON
- Terminal 30: 12.5V
- Steering angle display responds to steering wheel movement
- Damper valves could be activated (clicks heard upon commanding)
- 'Pressure change in central pressure reservoir test' was difficult to perform; possibly due to the Delphi being such a crappy thingy. The original pressure shown was 4.25 bar and using 'Pressure reduction' function I could run it down to 1.1 bar. Car height or height readings remained unchanged. 'Pressure increase' test would be immediately aborted. After these experiments, a.m. 'Pressure sensor' value (initially 0.41 Bar, 0.45V) showed the same as during the test.


Does anyone have any advice? Would you say that the car is resting on the rubber pads or not?

Maj. Dundee

Check for leaks.

Mika Riikonen

My wife had taken the car to an indie workshop.

Now, the story is somewhat vague as she is not technically inclined/interested. But here we go...

According to what they had told her, they had removed the compressor to test if it works, and after that reinstalled it. They had wiggled the wiring and connectors -and presto- the Airmatic works again. The workshop has no idea why the suspension works again, because all they had done was to remove and reinstall the compressor. So, no new parts, no nothing.

I am sorry that there is no better description available.

BlackML550

Reading up on this elsewhere it seems that one of the electrical connections to the compressor becomes worn with time due to rubbing on the frame. Thats probably why the giggling of the wires sorted it. Sorry i can't recall where I saw it (probably on this forum) but it was a consistent theme for many. If so, you'd want to reinsultate the connector which was one that went straight into the compressor.

Mika Riikonen

Thanks for your comment - I'll keep it in mind if/when the issue reappears.

So far the suspension has been working normally.

I just wonder why there never was 'Car too low' or 'Visit workshop' alarms...

BlackML550

I'm not convinced that the air Matic shows the right codes or notifications on the dash. All problems I've had with air Matic have never really shown up

Maj. Dundee

The Inst. Cluster does not show codes, it only tells you there is a problem.

BlackML550

Yes I could have worded that more appropriately. I didnt intend to imply you'd get a code on the dash. I've had both front and rear airbags fail and no notifications on the dash at all.

Maj. Dundee

You need this scanner.

Autel Scanner MD802 Maxidiag Elite

BlackML550

Thanks for the suggestion. I bought the icarsoft and am waiting for it to arrive. I know its not perfect but I'm hoping it will give me enough to do what I want to. There seemed to be enough positive reviews and its better than nothing. I have access to a Launch scanner as well if desperate so thats a backup.