I'm having issues starting my '09 S80. It wouldn't start a couple days ago, and the battery was reading low, so I put a trickle charger on it over night. I also cleaned considerable corrosion off the negative post. Started fine the next day. Today, the same thing happened. Battery was reading 11.6 volts. Took the connections off the battery and reattached, and it started just fine. With the car running, it was reading 14.2 Volts, so I assumed the alternator was fine. Here's the kicker: After turning off the engine, the alternator made a constant whine for about two minutes, and the volt meter showed it dropping from 12.6 to 11.2. Once the whine stopped, the draining stopped. I'm thinking a leaky diode, but don't know a whole lot about alternators or about Volvo's in general (it's my wife's car)

 

Those batteries tend to crack at the negative post which is what cause the corrosion. Maybe it is just the battery being bad not holding the charge. Are you sure the sound is coming from the alternator? Did you put a stethoscope onto it? Or was it coming from that general area?

 

Didn't put a stethoscope to it, but put my ear right on the alternator and it seems like that's where it's coming from.

 

Did you take off the entire intake system to listen to that? There are a lot of electrical component around the alternator .

 

No the intake system is between the alternator and the battery. The alternator is pretty accessible. I'm 99% sure that the whining is coming from the alternator.

 

The alternator is under the intake...

 

That's what I'm not understanding. I'm not entirely sure he knows where the alternator is or the correct year of the vehicle.

 

 

The silver thing with the two refrigerant lines going to it is the AC compressor.

 

Ahhh well that's my mistake then!

 

In that case, would it make sense for the compressor to be whining after the engine is shut off, and for that to somehow be draining the battery to 11 volts? It's just weird that the volts drop until the whining stops (about 2 mins).

 

If the clutch is staying engaged for some reason, yes, it could drain the battery. I've never seen this make a whining noise though.

Looks like you're gonna need a new battery and possibly ground cable too.

 

Ok thanks for the help. Going to change the battery and see if that fixes the problem.