Strange whining noise - possible alternator or AC compressor?

[Wolfie1]

Damn emissions control equipment! You know that stuff goes wrong more than anything else!

 

[JackBvmb]

Have a look at the vid i attached in post #10 he strips one down Jack.

It may be fixable but much easier to replace.

They are noisy things though they work on start up to blow air into the injection to help get the Cat converters going from from cold.

If anything goes wrong they usually throw a code P014 .... something i can't remember off the top of my head.

Mine makes the same noise but hasn't thrown codes up and is excellent on the emission from the car come MOT time.

I'll swap it out at some point but with no urgency do note though there is a relay that controls it i think (don't ask me which one) if it's on all the time it could be this.

In the summer months you may not notice it as much because the Cats warm up faster.

Brilliant, thank you for that. No it's not on all the time. Stays on for about a minute then goes off. Comes back on about 5 minutes later if the car is icy and left to idle to warm up.

So the car wont blow up if not fixed immediately.

I started watching the clip other day but it didn't sound the same. However it is the same part.

 

[chrisk2010]

Brilliant, thank you for that. No it's not on all the time. Stays on for about a minute then goes off. Comes back on about 5 minutes later if the car is icy and left to idle to warm up.

So the car wont blow up if not fixed immediately.

I started watching the clip other day but it didn't sound the same. However it is the same part.

As long as it is that then perfectly normal to me might be worth having the codes read to make sure there isn't an air injection problem and the emissions are correct then it sounds fine.

It scared life out of me the first time i noticed it so looked into and pointed it out to Mercedes at a service but they said they couldn't find anything wrong.

After some googling it seemed pretty common but there is this thread another member done with a similar problem:

W203 annoying secondary air pump fault

 

[JackBvmb]

As long as it is that then perfectly normal to me might be worth having the codes read to make sure there isn't an air injection problem and the emissions are correct then it sounds fine.

It scared life out of me the first time i noticed it so looked into and pointed it out to Mercedes at a service but they said they couldn't find anything wrong.

After some googling it seemed pretty common but there is this thread another member done with a similar problem:

W203 annoying secondary air pump fault

Thank you

 

[chrisk2010]

You're welcome