PeachParts Mercedes-Benz Forum - View Single Post

tinypanzer · #3 11-29-2010, 11:05 PM

I agree. Either a leaky diaphragm is robbing vacuum from the system OR the vacuum pump is starting to get weak and doesn't like being cold.

Listening for the pump running is the next step either way. When healthy, you'll hear it kick on after locking the doors and a second or so after the doors all lock, the pump starts to slow down as the vacuum rises, then quickly stops as the negative pressure sensor engages.

If it's leaking, you'll likely hear the pump run for a bit longer than normal. Once we verify that, the next step would be to remove the vacuum line from the pump and cap (seal) the pump. Running the same lock-time test this time, the pump should run only very briefly and shut off quickly since its output is now sealed. If so, then you likely have a leaky diaphragm as mentioned before. If the pump still runs a long time, or sounds like its struggling, then its probably the pump motor, or the pressure sensor inside the pump is out of whack.