S-Class (W220) 1999-2006: S 320 CDI, S 320, S430, S 500, S 600

Front not rising after upper control arm replacement

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Old Sep 8, 2017 | 09:48 PM
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2000 S430
Front not rising after upper control arm replacement

Hi, recently acquired a MY2000 S430 LWB a few months ago as a hobby/project car. Nice low mileage (<120K km, single owner example). And enjoying learning about the vehicle.

First of all, just want to say how much I am impressed by these MB forums. They are a great source of info and I have been using them a lot.

I have an issue which I am hoping someone can provide some insights into.

I just replaced the front end lower ball joints, both lower control arms and upper control arms on the vehicle. (There were some tears in a couple of the ball joints). However, now both front ends are no longer lifting and tires are not clearing the fenders properly.
1. The front was OK before the job. The rear is fine - have good height there.
2. I can hear the compressor running
3. Struts seem OK, no obvious leaks with soap test at the top.
4. Am quite sure I replaced the height sensors back on the UCA correctly
5. Get STOP CAR TOO LOW messages sometimes when I adjust the height sensor links (see below)

The previous owner had installed adjustable lowering links so I played around with adjusting them but no effect so far. I checked the sensor voltage readings and height levels after each adjustment (using iCarSoft MBII) and they do vary with each adjustment, so I assume sensors are working. What is interesting is that even with the front end down, the iCarSoft height readings seem to fluctuate around normal height levels (i.e. +/- 10mm). Whereas the front end is obviously 40-50mm lower than normal. Which suggests to me that possibly Airmatic computer thinks that the current low height is actually the normal height and therefore is not inflating the front struts.

Lift button works (and activates the pump most times). The active damping button also works - BUT the dash display reads different from the button display (e.g. when two lights show on the button (shock setting 2), the dash reads 'Convenience' mode. Again, which suggests the Airmatic computer is confused about something.

Before I start seriously digging into the pneumatics, hoping someone can provide any insights what be going on. In particuar:

1. Is it possible Airmatic is confused and thinks the current (low) height is normal? Can this be reset/calibrated by the dealer or other shop with proper computer equipment?
2. Are there other ways of pumping up the struts? E.g. Can I try pumping with the struts extended (i.e. front end jacked up)?
3. Is there something else I can try in adjusting the links (I suspect the after-market UCA's have slightly different geometry from the OEM's so the link settings will be not exactly the same, but can't see the settings so far off that the front won't lift at all).

Thanks in advance. And look forward to participating more in these forums.
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