I read somewhere that there is a vacuum hose between the pump and the valves to each door. I think a common failure is for this hose to split . When the pump is called to action no vacuum makes it passed the hose so the pump continues to run intil it overheats and trips out. Replacing the hose can fix the problem in some cases. Good luck. YMMV

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Tom Savage
Vienna, WV
1984 300D Euro
1995 S320