SLS=Self Leveling Suspension
What it basically does is it raises the rear to normal ride height whenever an extra load is placed at the back so the car doesn't "sag" at the rear.
If the system isn't healthy it's usually a bone jarring ride...OR an ultra floaty ride (no fluid left)
How would you know if you had one? Look at your rear shocks/struts...if they have a hose of any kind going through them then you have SLS...or a much simpler check, see if you have a hydraulic fluid reservoir up front that isn't for anything obvious. (vague I know
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85 190E 2.3(SOLD)
86 230E (-->300D) sold
87 300D (-->300TD) sold
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant) traded
86 190E 2.3... current project