Both driver and passenger seat lumbar adjustments on my 94 S350 do not work. Not sure if the vacuum supply pump is bad or is it not working because of some other cause. How can I test the system to find the cause of the malfunction?

Any help would be appreciated.

Sail42
94 S350
92 300SD / 500SD
87 E300D
85 300D
79 450SEL

The vacuum supply for the lumbar system is controlled by the pump underneath rear seat which is also for the rear backup indicators , trunk latch that pops out , central locking system , REST feature for a/c , and I think that is it . Usually the switches in the lumbar support go bad and leak vacuum. If there are any leaks in any of these systems it is best to have the problem fixed due to if the pump continually runs from leaks it will burn up. The new pumps have a update kit and they are not much fun to install. Best bet here is you may think about letting a shop do this , just for the fact of vacuum diagrams and knowledge of the system. Good luck

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euro 287
Mercedes Technician 7 Years (retired to Hyundai)
2000 Dodge Durango
98 Mazda truck

Check the fittings on the pump under the rear seat. Might be broken. If so, try to JB Weld them back on. MUCH cheaper to replace the pump yourself if it needs it.

__________________
1995 S-350
370K + SOLD
1952 220B Cabriolet
39K kilometers + SOLD
1998 E300D
310K +
2012 E350 BlueTec
120K

What kind of manuals do you have??

__________________
1995 S-350
370K + SOLD
1952 220B Cabriolet
39K kilometers + SOLD
1998 E300D
310K +
2012 E350 BlueTec
120K