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Alternator and crank sensor failure in BMW 128i

I have a 2008 BMW 128i with approximately 60,000 miles. I was recently told by the dealer that a rockl got lodged in the alternator, breaking the fins - which in turn caursed the crank sensor to fail. We have a good friend who is a mechanich and he tells us this is unlikely. Who is right? The BMW dealer also tells us this is not covered under warrenty. Could the fin braekage be caused by a manufacturing problem?

It is possible but EXTREMELY unlikely. Your engine compartment is pretty much surrounded by plastic shrouds, so the chances of a big rock getting into the blades on your alternator are very slim, unless your kid has been tossing rocks into your engine compartment while the hood was up. Your alternator is probably cooled by air that is ducted in from above the radiator to the rear of the alternator, drawn through the alternator by the fan at the front of the alternator.

What happened just before this problem manifested itself? Was anyone working on the car? A screwdriver or wrench left under the hood is much more likely to have fallen into the alternator and taken out the crank position sensor as it flew out. You are lucky that is all it destroyed.

I was at a light the car stalled it took a few times to restart. I took it to the dealer and they said it was the crank sensor a few hours later they called and said it was also the alternator- a rock got lodged in it and scraped the fins and seized the alternator and that then broke the crank sensor.

You most likely could never prove that they broke the alternator, but I have a real strong suspicion that you are paying for an alternator that they broke. Nothing you can do but pay the bill at this point.

The Lexus dealer damaged a couple of teeth on the wheel that the crank position sensor ‘reads’ on my brother-in-law’s GS while they were changing his timing belt. It still ran, but not quite right. He took it back and when they discovered the damage, they were very up front about it and gave him a loaner while they waited for the part and fixed it at no cost. Now they have a customer for life who trusts them completely.

Thanks, is it likely that a crank sensor would go at 60,000