W211 Self Levelling Headlight System

[MJH]

I seem to have an intermittant problem. Occasionally when I get in and start the car the lights stay in their lowest setting and don't adjust themselves. It then doesn't matter how many times I switch the lights on or off they won't reset.
If I then switch everything off, get out and leave the car, 9 times out of ten when I get back and set off again the lights will level up. But it seems completly random when it decides to stick.

Is there anything simple that can be checked or is it a diag's job ?

Thanks

Mike

 

[whitenemesis]

You could check the level sensors (attached to the front and rear ARBs). It may be one or other is very close to it's limits and depending how the car is sitting giving invalid values, the lights will default to lowest setting.

This really is easiest done on STAR

 

[MJH]

You could check the level sensors (attached to the front and rear ARBs). It may be one or other is very close to it's limits and depending how the car is sitting giving invalid values, the lights will default to lowest setting.

This really is easiest done on STAR

Thanks , that gives me something to go on. I wasn't sure where to start looking, as you say if all else fails she'll have to go in now the nights are drawing in.

 

[andy27168]

Hi,
I personally think this sounds like the levelling ECU is playing up, or possibly loosing its supply probably via a relay or such.
Either way i think you need to get it plugged into STAR for a diagnostic.

 

[Diesel Benz]

Hi,
I personally think this sounds like the levelling ECU is playing up, or possibly loosing its supply probably via a relay or such.
Either way i think you need to get it plugged into STAR for a diagnostic.

I think it is the levelling motor at the head light. Common issue, has been discussed at the forum before. I think Miro or some of the experts pointed to a spare part, for most current models the motor is not available as a spare part but a spare for another model may fit.

 

[andy27168]

I think it is the levelling motor at the head light. Common issue, has been discussed at the forum before. I think Miro or some of the experts pointed to a spare part, for most current models the motor is not available as a spare part but a spare for another model may fit.

The fault is effecting both of the headlights, both levelling motors to go at the same time seems unlikely to me

 

[Diesel Benz]

The fault is effecting both of the headlights, both levelling motors to go at the same time seems unlikely to me

Right, I missed that. If it appeared on both sides simultaneously, it sounds like it was somewhere else, not the levelling motors.

 

[MJH]

OK latest on this one, I bit the bullet and dropped it into a local indy last night. The diags are telling him that it's a communication problem between the two control units, one under the seat and the other under the bonnet. He's pulled the wiring and continuity tested it but can't find a problem and is struggling to work out what else it could be other than electronics. I've asked him to touch base tonight to let me know where's he's got to as it's sounding like he's not going to fix it and I need the car back tomorrow and also don't have a bottomless pit to pay him to carry on farting around with it for hours on end

 

[MJH]

Well the diagnosis now is that he thinks its the levelling control unit under the seat rather than the front SAM. So for now he's disconnected the light control and manually set the headlight levels so it's usable. The guy reckons he's spent the best part of 4 hours on and off through the day, he's also diagnosed an alarm sounder fault on the rear SAM and will give me the printout from the Star and the cost.... £100, which isn't as bad as I thought considering Merc quoted me £90 to book it in for the diags to run on it before any work. So for now the mystery continues and I need to go and find a control unit to try...........ebay here I come

 

[Nidjet]

Hi MJH,

Just wondering if you have solved this issue? If sodoyou have a part number for the control unit, as I think I may have the same issue.

Cheers

Chris

 

[MJH]

Hi MJH,

Just wondering if you have solved this issue? If sodoyou have a part number for the control unit, as I think I may have the same issue.

Cheers

Chris

Not yet, they're manually adjusted and module removed. So fine for now but I'm keeping my eye open for a module on the bay of evil or local scrap yards

Unfortunately the module is on the desk at work so I can't tell you what it is but to be honest I would say go and have the diags done first as it may not be the same and mine certainly isn't proven. The module I've removed is a small black unit under the drivers seat.

Mike

 

[Nidjet]

Cheers Mike, I'll get it checked out.

 

[MJH]

Bit of an update on this issue, not long after my last post I picked up a used unit for 40 notes. Fitted and all has been good since, but today it's back. Sometimes they adjust other times they don't, so either it's the same unit again or coincidence that when I changed it first time the original fault disappeared. So back to the drawing board for now, it can wait for it's next service.

 

[Khan80]

Hi, I had the same problem and booked in today and my garage has come back with load sensor problems. So they need to book the car for two days so find out which one is playing up.

I will update later when i receive the car back with the solution.

Thanks

 

[b1g1an]

You could check the level sensors (attached to the front and rear ARBs). It may be one or other is very close to it's limits and depending how the car is sitting giving invalid values, the lights will default to lowest setting.

This really is easiest done on STAR

If you've got air suspension does that do the levelling instead as mine don't nod like every other car I've had but they've all been normally suspended.

 

[BlackC55]

I would try a star re-set first.

 

[PR1]

If you've got air suspension does that do the levelling instead as mine don't nod like every other car I've had but they've all been normally suspended.

I have the estate (s211) with rear air suspension, but my lights still nod as you put it. Well they did until they got stuck in the low position.