Granted, this procedure almost unworthy of a Photo DIY! But I think many (such as myself) left most underhood matters to the dealership technicians while the car was under factory warranty coverage. And given the expensive implications (pump damage, etc) if your ABC fluid level isn't maintained, this is probably something everyone should stay on top of.
Sample car is my 2005 CL500, chime in if there are significant differences in other years/models. We are at the right front of the engine compartment (driver's side for left-hand drive cars) as you stand at the bumper looking back toward the engine.
First, the location of the filler/dipstick plugs. (Indicated here by yellow arrows.) There are two and they merely pop off with a squeeze and a pull (they are not threaded). Although the power-steering and ABC systems are interconnected, their reservoirs are separate. The upper, larger one is ABC and the lower, smaller one is for power steering. The larger fittings with the teal-colored labels are the filters.
Once removed, the dipsticks look like this (this is the p.s. one; the ABC one is longer). There are two markings... ***Edit thanks to our resident expert Eric:
"Fluid should never be mid range, at the upper detent with engine off, lower detent with engine on." If mid range with engine on then there is too much fluid.
Apparently you can
remove them while the engine is running because my mechanic filled them through a clean
funnel (highly advised) while the car was idling. And you thought this was DIY
note 'official' instructions
indicate that engine should be switched off!
And now, the secret elixir: M-B Hydraulic Oil Q1 32 0001 (Pentosin CHF 11S; Product Code 1408107). Known colloquially as "ABC Fluid"!
Upon which it clearly states: Do NOT mix with other fluids
. Insofar as a couple of members here have apparently experimented with admixtures of this and power-steering leak stop. I cannot in good conscience recommend such a strategy, particularly since those members were never heard from again!
This stuff costs about $37.50 per liter at your dealer. If your W215 has more than 25,000 miles, though, I'd consider the investment. You may never need it, but if you did, wouldn't you want some handy?
PS: See this post
for a less-costly alternative Pentosin source. We still need some confirmation on any possible issues with respect to the alternates though. I expect it's the same thing.