BMW Alternator Pulley - Genuine BMW 12311247312

Product Information

BMW Alternator diagram for 318i, 318is, 318ti

An Alternator Pulley is the wheel attached to the alternator shaft that connects to the engine’s serpentine belt or drive belt. As the engine runs, the belt turns the pulley, which spins the alternator’s rotor and generates electricity to charge the battery and power the vehicle’s electrical systems.

Many modern vehicles use an Overrunning Alternator Pulley or Overrunning Alternator Decoupler, which has a clutch-like mechanism that allows the alternator to "freewheel" when engine speed suddenly drops. This reduces belt vibration and improves efficiency.

• Squealing or chirping noises – especially at startup or when revving the engine.
• Battery warning light on dashboard – alternator isn’t charging properly due to poor pulley function.
• Intermittent charging issues – lights dimming or electronics flickering from unstable alternator output.
• Excessive belt vibration or wear – serpentine belt jumps, slips, or frays.

About Genuine BMW

The original parts used by BMW to build your car are available as replacement parts under the “Genuine BMW” brand. When ordering a Genuine BMW part you are guaranteed to get the same part that you would pick up from your local dealerships part department. Genuine BMW parts have been built to BMW’s stringent standards and are the same quality of the original parts used to build your Ultimate Driving Machine.

You may not realize this, but the parts that make up your BMW are not necessarily manufactured by BMW. No cause for concern, as BMW designs the part, hires a manufacturer, and ensures its quality to you. In fact, many of these manufacturers have been making parts for BMW for decades. In our industry these manufacturers are called OEM (Original Equipment Manufacturers), and these are often brands you recognize, including Lemforder, ZF, Sachs, Bosch, Valeo, Zimmermann, Siemens VDO, Corteco, and more. Don’t be surprised to open that Genuine BMW parts box and find an OEM branded part inside, simply with the addition of a BMW logo.

Be sure to keep an eye out for OE tags on our product pages to quickly identify parts coming direct from OE manufacturers. That extra bit of insight could save you some serious money while shopping! Refer to our OE Academy for further information regarding the OE/OEM tags throughout the site.