I am getting code 21 (pressure switch). The ASR pump is running, but doesn't seem to be making any pressure, and when I open a line there in no fluid coming out, tore the pump down, it all looks good. So is the Charging pump responsible for getting the fluid to the ASR pump? I have been searching for a schematic to help me see exactly how the system works and what lines supply what, but to no avail.

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Mercedes Fleet:
2004 CL600 Designo Espresso SPORT
2004 S600 Designo Espresso SPORT/Lorinser Pkg.
1999 S320
1988 300TE
1972 280SEL 4.5
Diesel Fleet:
2014 GL350 Blutec
1987 300SDL Blk/Blk 4 place seating #18 head
1987 300SDL Smk Slv/Burgangy #17 head
1986 300SDL Blk Pearl/Palomino #14 head w/ 280K
1984 Lincoln Mark VII Fact BMW Turbo Diesel