(I thought I'd post this proactively in case it's helpful to people searching in the future. I see related questions for other models here on MBWorld, but none specifically for the X166 to attach this to. It's very basic for anybody with experience, but not everybody has that. The task was technically simple, but dirty and a little frustrating at times.)

Problem: 2017 GLS450 windshield washer started losing pressure, then stopped altogether. (After fixing, wife thinks it had been degrading gradually for years.) Washer fluid reservoir had plenty of fluid, and weather was mild.

Likely candidates: Pump or Grommet (item 12 or 13 of https://www.mbpartsgiant.com/parts-l...her-components), but the gradual degradation & description on this forum of frequency of issues made me strongly suspect that (& that was it).

Tools needed: 8 & 10 mm sockets, clip puller (ideal, probably could manage with variety of flat screwdrivers).

Procedure I followed (not to say its the best, but it worked for me 1 out of 1 times):
- Remove fender inner liner (left):
- - (I removed the headlight access panel within the larger liner, but don't think it was necessary in retrospect.)
- - Remove pull clips around inside of liner. These are typical two-part auto clips with an inner pin that when pushed in expands the outer part for grip. First pull out the small inner button out (I used a tack puller because it was finer than my clip puller; doesn't need to be all the way out just ~3/16" but all the way works too), then once that's out pull the whole clip (I used my clip puller for this). I believe 3 of these.
- - - (Somewhere in the process I had to steer the wheels all the way left for access)
- - Unscrew two plastic nuts (one near top of inner fender facing down; other on inside of fender facing out)
- - Unscrew 4 screws attaching liner to splash guard under the nose of the car. These are all facing down, on underside forward of the wheel well.
- - Remove the semi-rigid liner completely
- Position container to catch fluid under the fluid reservoir (a pretty big one, since the fluid kind of fountains up once the pump is removed then runs back off the reservoir - not a compact stream)
- Pull the pump out: It is NOT latched in place in any way. It is retained only by gravity and seal friction (it has a long "nose" projecting down into the grommet), so just wiggle-rotate (within slight range of motion allowed) while pulling up. I didn't disconnect any wires or hoses.
- - (I was able to sit up between the wheel/tire and frame to work)
- Pull the grommet out
- For me, all I had to do was clean the grommet. I used soap, a fine brush, and hot tap water flowing the opposite direction of what fluid going into the pump would flow.
- - (If you needed to replace the pump, you'd have good access to hose connections & wire connector at this point. Though I looked at the hose connections a bit, and it was not obvious to me how they worked.)
- Reassemble reversing the whole process

 

Nice work! Thanks for sharing.