The alternator is driven by belts in the engine, where it produces an alternating current, which is converted internally to 12 volts direct current by the diode bridge or rectifiers. Diagnosing your BMW 435i alternator can be tricky because when this part fails it can present a whole host of different symptoms. In addition, a failing BMW alternator will fail gradually until all electrical accessories in your car will not work and your car finally dies. Fortunately, we offer a great selection of new and remanufactured 435i alternator products, including high-output replacements for you electronics junkies.