Lost power steering and alternator at the same time
 

At slow speed, suddenly the power steering quit. Then I saw that the battery light was on, no alternator output. Then I smelled rubber burning. I shut off the motor right away.

It was the serpentine belt. I looked it over where it was visible but saw no obvious problem. I tried starting it up again and the belt started smoking before I had time to see where. I decided not to destroy the belt by troubleshooting it, shut the motor off again, and went to get our big trailer to tow the X5 home.

An hour later I jockeyed the X5 to put it on the trailer. The power steering worked for a few seconds, then quit again and the battery light came on. Once the trailer was in place, I started the X5 up to drive up the ramps, and the problem was gone. I had power steering and the battery light stayed off.

WTF could do this? Some component on the serpentine belt must be seizing up. I am going to leave the X on the trailer and take him to the indy tomorrow, if he has time to take it.

This is not a problem I have ever had before with a BMW or any lesser car. Weird! Has anybody BTDT? (been there, done that)

idler/tensioner pulleys when did you last replace them?

The indy did those in January. He showed me the old ones, which were well knackered, to say the least. Perhaps I got a defective unit.

Best to remove the belt and give all the pulleys, idler pulleys a spin and see if you feel or hear any roughness. Could be an alternator bearing that is seizing up.

Yup, looks like something dragging.

Removing the belt and inspecting the entire accessory drive system is a good idea.

If this is for the 3.0d m57 diesel motor, the main pulley likes to fail on those. The rubber damper could be failing or shredded already.

Yup, looks like something dragging.

Removing the belt and inspecting the entire accessory drive system is a good idea.

If this is for the 3.0d m57 diesel motor, the main pulley likes to fail on those. The rubber damper could be failing or shredded already.

Yep, it's the M57N. I had not heard about that main pulley issue. I've seen them fail on Saabs but the failure mode is freewheel instead of seize. Thanks for the tip!

I doubt this problem is going to be the main pulley. If it fails, it's not likely it could seize. More like fall off...

Unless it HAS fallen off and jammed against the radiator, but I'm guessing you would spot that. And you say it came right long enough to get the car onto a trailer. So not the main pulley then.

This has to be a failing driven component. Water pump? Thrown an impeller blade and it's jamming, then freeing up?

Let us know what the Indy finds.

*edit* Thinking some more about this, even if something else fails and the belt keeps moving (which it did - it was smoking), the alternator should have still been driven and producing an output. If the alternator output fails when the belt is smoking, it's likely that it's the alternator that is seizing. Maybe...

I dropped the X off at the indy and he showed me a crank damper. Once it's in hand, you can see how it would fail. Its large rubber inner component breaks down and de-laminates from the inner metal core and outer metal pulley. This produces 1) smoke and 2) little chunks of rubber visible below the area, whilst the serpentine belt is not fully driven. Hence the weak power steering if any, and the alternator warning light.

The little chunks are what we saw on my car. What I thought was smoke from the belt was in fact smoke from the damper. He says it's pretty rare, but obviously it does happen. He sees it more often on the E39.

Hope this post helps somebody else with a similar M57 problem some day!

So the smoke was from the failed main pulley (damper) and not the belt? Ok, that changes things. ;)

Glad you got it sorted and I'm glad we can all add this to our collective diagnostic knowledge - thanks for the update. :thumbup: