2009 BMW 135i Alternator Replacement Cost

When there is any failure in the starting and charging system, the entire system must be tested. Repair shops use professional test equipment that checks every component simultaneously and definitively. If the alternator is the problem, it will be identified.

When replacing the alternator, the technician must remove the battery cables to prevent electric shock. The accessory drive belts or serpentine belts must be removed from the alternator, along with electrical connectors and several bolts. Once the bolts are removed, the alternator is free from the alternator brackets, and can be removed. Replacement is in reverse order, and proper torque must be applied to prevent damage. The vehicle will then be retested.

Because the alternator requires the removal of the serpentine belt, this is a good time to replace that belt if it's worn, or the service interval has been reached. If the battery cables have physical damage or extensive corrosion, they should be replaced as well.

On some cars, it can be hard to access the alternator, and that can play a significant role in the repair cost. In some cases, suspension components, drive axles, cooling fans and even bumpers must be removed. If the vehicle has after-market electrical components installed, the new alternator should be strong enough to handle the additional power demands.

If the alternator is tucked away and hard to get to, the replacement should be left to a professional technician. If the alternator is more easily accessible, and you have a good understanding of the starting and charging system, you should be able to diagnose and repair this problem yourself.