ML320 Year 2000 Petrol

Dean ML320

New Member
Jun 27, 2010
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Your Mercedes
ML 320
I wonder if anyone can help me?
I have owned an ml320 for nearly a year, low mileage , no problems.
Today I drove for about 3 miles and stopped and could hear what I thought was a fan running. I thought it is hot its just the fan, anyway after 20 minutes it was still running, its not a cooling fan its the fan under the engine plastic cover at the top of the engine right at the front. It wont turn off and I've had to pull the electrical connection plug to stop it running.

I have no idea what this fan is for , ( turbo prehaps ), can you help??!!!


Alex Crow

Senior Member
Jul 9, 2009
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Super Suffolk
Your Mercedes
W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
i think you are describing the secondary air injection pump - black plastic housing held in aluminium bracket at top center of engine. this should not be running at all when the engine is up to temp, and it is hard to understand why it is running constantly. its purpose is to aid catalytic convertor warming, and i have never heard of one running when it should not. from memory i am unsure of which output stage powers the air pump, but i would suggest it is worth checking the relay descriptions in the fusebox lid. if there is a relay dedicated to the pump then pull it out, reconnect the pump and see what happens. if it is not running then put the realy back in, if it still runs constantly and with a hot engine try swapping the relay with another one - there will be several similar ones in there. if this cures it you need a new relay.

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