I have copy of the MB-WIS but for some reason it won't install on my new computer so I am hoping somebody can help identify a part and give some advice on what to do about it.

The problem is that when I start the car, I get a high pitched sound which I think is the serpentine belt rubbing against a frozen pulley. The offending part is at the left most side of the belt path (passenger side) and looks to be attached to a pump or something like that. It might be electrical since the ABS and traction control idiot lights are illuminated, and the owner's manual says something about a low voltage condition, but it doesn't look like an alternator to me since there are no cooling vents on the piece.

I assume the pulley should be more or less perpendicular to the shaft, but it seems to be cocked to one side by 5 degrees or so, which suggests that the bearing is shot. Should I replace the whole unit or can I just replace the bearing? It doesn't look like a huge problem to get to it but I would like to know what it is so I can get the right part on order and I don't think it is a good idea to drive it to the dealer in its present condition.

Sounds like an alternator, especially the fact the ABS light being on. ABS doesn't start till the alternator works.

If there is a change of position due to the failure it is unlikely that just a bearing will solve the total problem. The armature usually hits the field windings in such conditions.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Your Owner's Manual on page 126 has a diagram of the serpentine belt for the S320 which should allow you to identify the pulley.

Steve,

Thanks for the response, but after much Googling I found the answer and it is not the electrical (I obviously have more than one problem).

I found a description of my problem that fits exactly:

Emissions air injection pumps can seize up, causing a loud squealing noise possibly followed by smoke. The air pump pulley stops turning, but the drive belt does not and this friction causes the noise and smoke. If the engine is not turned off, the belt will snap, turning on the alternator/battery warning light.

My same question still applies - do I R&R the entire pump or can I repair just the bearing?

I was just going to post that the fact that you have pulley deflection probably means you have a air pump issue as it has a clutch on it which does really fall apart when failing. It is probably keeping the belt from driving the alternator properly which is the electrical problem.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician