BenDaniel

I have an 03 E500 and had previously replaced the rear airmatic system with Arnott bags due to the "standard" failure, plus the right front a few weeks later. It's been running fine like that for 6 months, and now finally the left front was on the ground this morning. Picked up the new Arnott part locally this afternoon and installed it, so now all 4 corners are new Arnott parts.

Problem is now (and honestly, I didn't think to listen to the pump before I replaced the 4th corner today, so I'm not sure this is new to *after* what I did today or if it was happening before as well) that the pump won't turn on at all when I open the door or start the car as I would expect - not even if I push the "raise car" button in the center console, although the light does come on.

In troubleshooting, I checked the relay and it is correctly open when at rest and closes properly with 12v to the coil - I do not have a regulated power supply, so I can't test lower voltages (more on this in a second). I jumped the contacts at the relay socket (pins 30 and 87) and the pump comes on as expected, albeit somewhat rattle-y. When I test voltage at the relay socket with the key to "off", 85 and 86 are open with 0v to ground (this is the coil circuit, and this is expected when not energized). There are 12v on pin 30, and 87 is open (this is the pump circuit, which should close when the coil is energized by the Airmatic computer subsystem). With the key to "on", there are ~5v on 85 and only 11.4v from 86 - not sure why both are showing positive voltage, I would expect 85 to be ground if 86 is almost 12v... Since I can't test 11.4v to the relay without a different power source or more stiff wire that I don't have access to at 1 AM, I can't verify with a multimeter that the relay is in fact switching with 11.4v. It's rather noisy under there with fans and relays clicking all over, but with a stethoscope on the pump relay housing and an assistant turning the key, it *sounds* like the pump relay is clicking on and off when the key is turned from position "off" to "on" and back, but I'm only about 80% sure I'm hearing the right one. My back is hurt and I can't get under the car to put a multimeter at the pump connectors tonight to see if it is in fact getting voltage from the relay, but will try in the morning if I can muster the strength.

All of this leads me to understand that:
A.) There is power available to the relay coil (no fuses are blown upstream)
2.) There is power available to the pump on the relay socket (fuses ok again)
C.) The relay is functioning properly at 12v, and it appears to work at 11.4v but that's not verified yet
C.) The pump is functioning properly - or at least is capable of turning on if given 12v.
E.) I really need a lift in the garage

Assuming I'm correctly hearing the solenoid click in the relay and it is functioning at 11.4v, why won't the pump turn on to fill the new strut? I recall having to let it run for several minutes to fill the system when I did the other corners, but since the pump won't turn on at all right now, it's obviously never going to fill at this rate. I would expect that a bad connection at the sensor would have resulted in an airmatic warning on the dash, but all I get is the red "stop - car too low". Will double check the new strut's electrical connections in the morning as well.

Going to bed in agonizing pain, will check for overnight responses and answer any questions in about half a day.

Thanks in advance

BenDaniel

ok - little more info...across 85 and 86 (not sure why I didn't test ACROSS them before, was tired I guess) I get a floating value of 7.5v with the car off, and 7.21 exactly every time I turn it on. Obviously not enough to throw the relay over. That means there is no signal from the computer to turn it on, which I presume is for safety due to an unplugged or loose sensor (and I can't see the dashboard error due to the "car too low" screen which overrides everything else)

So I presume it's a sensor or other electric plug after all, will keep this thread updated for posterity once I fill my stomach with enough meds to get under it again

cmriv

If your pump is receiving 12vts or any voltage at all and your ride height doesnt adjust and you can here everything clicking and what not, you gotta bad pump.... simplistic. If you found someone with star youd be able to do the pnuematic test for these compressors....

BenDaniel

The relay itself was not being energized (meaning the pins supplying energy to the coil itself didn't appear to be turning on) - not sure how a bad pump could possibly cause that to happen...but just in case there was some sort of circuit sensing going on that wasn't switching on the appropriate current because the computer sensed the relay was failing, I replaced the relay - and the pump now turns on as expected and pressurizes the system properly. Went through several "up/down" cycles from the center console button, worked as it always has in the past. It even seems a little less noisy somehow, but that could be my imagination.

There is a small internal resistor across the coil of the relay, and out of curiosity I tested the resistance of the old and the new relays across pins 85 and 86.

The old relay was part # A002 542 13 19 and had a value of 75 ohms
The new relay is part # A002 542 72 19 and has a value of 90 ohms

Not sure if the difference in resistance was key or if there was a failure of the old relay (again, I don't have a bench power supply to test with a known current, but hooking directly to a 12v PC power supply makes the old relay close - perhaps there is a resistor farther up the circuit that limited the current to the point where it wouldn't energize enough to close...dunno.) Either way, a $15 part (on top of the 4 new Arnott struts and bags) fixed my issue. Hope that helps someone else down the line.

I still need a lift in the garage, though. Next house we build, even if it means the wife doesn't get a swimming pool.