at trafflic lights, i can hear some motor kick in and my lights dim. what is this? - PeachParts Mercedes-Benz Forum

ProV1 · #1 12-21-2006, 10:19 AM

once a while when i'm stopped at a traffic light, i can feel/hear some motor kick in for a few seconds and then it stops. when the motor kicks in, my dash cluster lights dim for a split second too.

what is this motor and what does it do? it must be drawing lots of current to dim the cluster lights

GSMITH · #2 12-21-2006, 11:03 AM

Can you tell where the motor noise is coming from?

whunter · #3 12-21-2006, 11:12 AM

Normal operation.

This is your electric auxiliary cooling fan turning on.

Have a great day.

ILUVMILS · #4 12-21-2006, 12:11 PM

It's probably the secondary air injection pump. Some people say it sounds like a vacuum cleaner. Is it a really high-pitched whine?

whunter · #5 12-21-2006, 01:28 PM

Quote:

Originally Posted by ILUVMILS

It's probably the secondary air injection pump. Some people say it sounds like a vacuum cleaner. Is it a really high-pitched whine?

Possible:
I only had one bad enough to dim the lights, and it shorted seven days later.

ProV1 · #6 12-21-2006, 02:20 PM

Quote:

Originally Posted by ILUVMILS

It's probably the secondary air injection pump. Some people say it sounds like a vacuum cleaner. Is it a really high-pitched whine?

yes, sorta sounds like a high pitched whine. is that bad?

ILUVMILS · #7 12-21-2006, 06:17 PM

Quote:

Originally Posted by buckwheat

On my motor's program (119), air pump is only on during initial start for 60 seconds. Blows more O2 into the cats to help them come up to temp. I have never found a trigger for this at other times - please help me verify. And you're right, it's quite similar to a vacuum cleaner/blower.

Air injection does indeed take place following cold-engine start, but the system self-test takes place after the coolant temperature is above 60C, and the vehicle comes to a stop.