Comprised of diodes which can exert 12 to 14 volts DC, the BMW 740il alternator powers various electrical components in your car such as a power sunroof, built-in DVD player, and heated seats. More importantly, the alternator is responsible for providing your car batteries with the necessary electrical charge. When the alternator of your car goes bad, you can expect a number of malfunctioning symptoms such as misfire and an ABS light on. It can even get worse and cause start failure because of the uncharged car battery. To help you figure out what's wrong with your BMW's alternator, here are some signs to watch out for and what they usually indicate:
Your BMW 740il's alternator has diodes inside it that transform the alternating current into a direct current. This conversion leads to the creation of a charge that powers the battery. To check if the alternator is bad, disconnect the battery while the vehicle is running. If the car continues to run like nothing happened, then your alternator is doing just fine. However, if the vehicle immediately stalls and shuts off, then your alternator is obviously busted.
The alternator has a rotor inside it, which spins on a set of ball bearings. When these bearings within the alternator become worn, they can "catch" as they develop flat spots. This results in a horrible racket and can turn into a sustained grinding noise. Verify bad alternator bearings using a tubing to listen for noise. While your car is in idle, put one end of a 12-inch piece of tubing near the alternator, while the other end of the tubing is placed near your ear. If the noise is louder near the alternator, then that's an indication of a bad alternator.
When your car's alternator loses ground, it can lead to expensive damage as the alternator surges, posing a malfunction possibility to the voltage regulator inside it. Inspect your alternator's primary mount to see if it's still wired to the vehicle's frame. A large cable usually connects the alternator to the car. Over time, this cable can become loose or disconnected. Make sure that you tighten the connection of the ground wire to the alternator mount, and inspect it regularly.