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Old 10-06-2003, 09:20 PM
Rookie DIYer
Join Date: Jun 2002
Posts: 106
Random Vacum Pump Noise from Trunk C280

I have fixed my headrests, rough idle, and trunk lock vacum problem. My only problem that i still have is the trunk vacum button not popping the trunk lid or the remote key opening the trunk with the double click of the button. I have no real urge to fix this but...

I hear the rear vacum pump which is on the right side of the trunk randomly go on and off when i am driving or in park. It makes a noise like it is working and then after about 45 secs. starts pumping again. I don't really know why, logic makes me beleive that there is a leak and it has to keep working due to a leak, but i dont really know.

I appreciate all the help, this forum has been a great learning tool for me
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Old 10-09-2003, 03:05 AM
David C Klasse's Avatar
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Join Date: Jan 2001
Location: Mission Hills in the City of San Diego
Posts: 2,352
SOUNDS to me like a vacuum leak... the pump will stay to perform it's duty if the vacuum is not correct. It automatically turns off if it's threshold/duty can't be performed. If it's cycling automatically when driving, and nothing is activating the pump (door locks, cruise control (?) or climate control vent doors) then it sounds to me like maybe a switch problem somewhere? (Maybe your trunk door sensor?)

Good luck.
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Old 10-09-2003, 08:17 AM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
A/C vacuum leaks are the most common. The fresh air vacuum element is a common failure. Try using the EC button for a while & see if the pump stops that on/off cycle.
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