Cupertino Auto Repair

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10100 Bubb Rd.
Cupertino, CA 95014

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Bad Alternator or Battery Might Stall Your Car

Written by maryp posted on Wednesday, April 6th, 2011

5.00 avg. rating (92% score) - 1 vote

Having a tow driver “fix” your BMW is like asking the person driving you to the hospital to diagnose your appendicitis attack! Think about it.

Your BMW or MINI won’t start and the battery seems like it has died. Now what?

It is time to check your battery for state of charge, and state of health. Age of the battery is also a consideration and should be recorded at your shop. If your battery is OK, it is now time for a complete charging system check which includes:

  • Checking belts,
  • tensioners,
  • pulleys,
  • test of the starter (initial and cranking) and the alternator performance (voltage and amperage output,
  • diode stator condition and voltage regulator control and voltage),
  • and parasitic drains.

Based on all of these test results vs. the BMW specs, we could recommended a battery or alternator, or continued diagnostics. Why? The battery test will tell us how much life is left in the battery approximately. Your battery may have just ended it’s useful life and that could be all that is needed. Or your battery could be damaged by a bad alternator and that could be a reason for a recommendation of both. Or your alternator has just begun to go bad and your battery is OK. BTW, we have to use a new battery to check the alternator outputs. That is the only way to get an accurate baseline of your alternator.

A BMW may keep running, but a weak alternator, and it’s lack of output will cause the battery to work harder. This in turn causes excessive heating in the battery, which will usually result in corrosion from out gassing as the condition continues. In other words, an alternator that is not working at it’s 120 amps can result in damage to not only a battery, but control units, too. You don’t want that to happen!

If at all possible, take care of problems on your BMW that if left undone, can lead to a more expensive repair down the road. That is not fun for either of us.

BTW, we know that summer driving will be here soon. The hot weather will bring on a spate of battery failures. Let’s check yours out now, before you get stranded. And please, if you are calling a tow driver, have them TOW only to your independent BMW or MINI professionals or a dealer.

5.00 avg. rating (92% score) - 1 vote

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