W211 air suspension relay low voltage

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chris116

Member
Joined
Oct 13, 2014
Messages
49
Car
w205
Hi,
Any assistance on the following would be much appreciated.
Returning to to car I found the rear end fully down with the red ‘car to low’ dash warning.
Early stages of checking things through found the compressor relay Ok but no voltage at relay block terminal 2 (load supply from pre-fuse 74) dead short at terminal 8 (load supply to compressor). Suspect compressor or wiring fault and blown fuse 74 unable to confirm as yet due to poor weather and having to work outside. ⛈
However terminal 4 (relay coil voltage from controller) only shows 4.2v as my OBD reader can’t access suspension fault codes so I’m unsure of any pending codes in the controller.
Can anyone please answer the following;
is the low voltage likely to be the controller thats u/s or can this be caused by an error code?
How do you gain access to the Pre-fuse box? are the fuses a standard blade fuse and how are they removed?
Where is the controller located?. Is it possible to obtain a part number for this? Vin is WDB2112222 2006 wagon RH drive

Many thanks in advance
Chris
 
Position the prefuse unit varies- the front one is often found under a kickplate in the passenger/driver footwell or beside the battery- rear one under the rear seat or behind boot side trim /wheel well --difficult to tell from rhd/lhd images. The prefuses are fusible links bolted in place [ can be found online , ebay etc] I think MB only supply complete prefuse units? Plenty of info on here if you do a search on "prefuse"
Help please Urgent?
 
2002-2009 Mercedes-Benz W211 (E-Class) Fuse Box Diagram
There's about 3/4 different fuses and relays for the airmatic
Thanks all fuses and relays are good the fault I was referring to is low voltage from the control unit and no voltage from the front pre fuse for the compressor. I still need to check compressor and wiring but without 12v at the relay from control unit I believe I’ll still have a fault
 
Position the prefuse unit varies- the front one is often found under a kickplate in the passenger/driver footwell or beside the battery- rear one under the rear seat or behind boot side trim /wheel well --difficult to tell from rhd/lhd images. The prefuses are fusible links bolted in place [ can be found online , ebay etc] I think MB only supply complete prefuse units? Plenty of info on here if you do a search on "prefuse"
Help please Urgent?
Thanks for this that sounds a PIA to get to then. Any thoughts on the low voltage from control unit to relay? I think that is where I’m going to be stuck
 
Very useful mate thanks. I’ve got an auto electrician coming to scan the OBD to try and locate the low voltage at the relay coil. I’m hoping to check compressor and wiring Saturday but rain forecast again getting too old to be laying around on the wet floor. I’ll post an update if I find the answers
Thanks for your help on this
 
Hi,
Any assistance on the following would be much appreciated.
Returning to to car I found the rear end fully down with the red ‘car to low’ dash warning.
Early stages of checking things through found the compressor relay Ok but no voltage at relay block terminal 2 (load supply from pre-fuse 74) dead short at terminal 8 (load supply to compressor). Suspect compressor or wiring fault and blown fuse 74 unable to confirm as yet due to poor weather and having to work outside. ⛈
However terminal 4 (relay coil voltage from controller) only shows 4.2v as my OBD reader can’t access suspension fault codes so I’m unsure of any pending codes in the controller.
Can anyone please answer the following;
is the low voltage likely to be the controller thats u/s or can this be caused by an error code?
How do you gain access to the Pre-fuse box? are the fuses a standard blade fuse and how are they removed?
Where is the controller located?. Is it possible to obtain a part number for this? Vin is WDB2112222 2006 wagon RH drive

Many thanks in advance
Chris
Ok I found and replaced the 40amp prefuse number 74 can somebody tell me where the rear axle level controller is located? Still only getting 4.2v at the relay. Wiring diagram shows this as fed from N97 rear axle level system control unit pin no 16. I believe my part number is A 2515450432 but I can’t find it.
Any suggestions welcome
Many thanks in advance
 
Well it is normally just in front of the rear axial on the passenger side,it looks like a box the size of a packet of fags with a small arm coming from it, it is a potentiometer ,if you look on ebay there are some for sale it would give you a idea what they look like,one of the faults is that the arm on many is made out of plastic and it cracks,and I believe you can only get the whole unit from MB.
 
Well it is normally just in front of the rear axial on the passenger side,it looks like a box the size of a packet of fags with a small arm coming from it, it is a potentiometer ,if you look on ebay there are some for sale it would give you a idea what they look like,one of the faults is that the arm on many is made out of plastic and it cracks,and I believe you can only get the whole unit from MB.
Cheers Zipdip, If it has an arm I think the part you’re referring to is the level sensor I’m I correct? the item I’m looking for is the level controller as far as I can make out it’s in the passenger side footwell near the prefuse. I’ve exposed the prefuse unit to change fuse 74 but no sign of the control unit
 
Cheers Zipdip, If it has an arm I think the part you’re referring to is the level sensor I’m I correct? the item I’m looking for is the level controller as far as I can make out it’s in the passenger side footwell near the prefuse. I’ve exposed the prefuse unit to change fuse 74 but no sign of the control unit

Thats where I would expect to find it. [ any other kick plates towards the bulkhead area of the footwell?? other locations might be under the rear seat squab or behind the load area/boot side trim sapre wheel well.
https://www.google.com/url?sa=t&rct...airmatic.pdf&usg=AOvVaw2eqp20ZaZgijgQ3YSQjlVM
 
Thats where I would expect to find it. [ any other kick plates towards the bulkhead area of the footwell?? other locations might be under the rear seat squab or behind the load area/boot side trim sapre wheel well.
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=2ahUKEwjd0s_kwoDmAhWisXEKHewRDEMQFjACegQIAxAC&url=https://mbworld.org/forums/attachments/e-class-w211/422042d1567884612-diagnosing-airmatic-compressor-airmatic.pdf&usg=AOvVaw2eqp20ZaZgijgQ3YSQjlVM
Many thanks for this what a great article really useful. I’ve not had another look for the module yet as I’m fed up getting wet and cold after removing the compressor but judging from the pics I think it’s under a plastic cover on the floor pan I’d not looked under this as I thought I was just a cover for the seat wiring. After speaking to an auto electrician he thinks the relay coil voltage at 4.2v maybe normal if fed from a control module I assumed it should be 12v. A simple test with a test lamp to the compressor feed cable will prove this
Many thanks again for your help on this
 
I get the replacement compressor tomorrow hopefully a warranty replacement from ecp as it’s only 6 months old I want to replace the filter and relay. I replaced the relay last time From ecp and it still appears to be Ok but the part number appears incorrect mine is a Tyco A0025421319 the parts catalog lists this as a secondary air pump relay with the correct number as A0025422319 when compared to other posts I’ve seen on here the umber is for a Hella A0025427219. Can anyone confirm if mine is correct and/or confirm the upgraded part number and where to get one please. Car is 2005 W211 320CDI estate
Many thanks again
Chris
 
HELLA Aftermarket Catalog - Multifunctional Relay
these are general purpose relays and are used for many switching applications in many MB models- see the listing They all have the same pin connections with a relay coil wired in parallel with a resistor but may differ in their current switching capability- this one is 40 amps@12v
Relay, main current HELLA 4RA 007 791-011 — Buy now!
Many thanks again Graeme, you’ve been a great help with this. The car’s now up (pun intended ) and running. Old compressor was exchanged under warranty I’ll be keeping an eye on it as the old unit was only fitted in April. BTW the exchange unit was supplied with an unbranded relay
 

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