OEM Bosch Voltage Regulator IB521

Specifications

• MFR: BOSCH
• FEATURE 1: 100% New
• NOTE 1: BSS
• SPECS FOR: Bosch IR/IF
• SPECS: 12 Volt

Used On

• BMW (2003-2006)

Replaces

BMW: 12 31 7 515 319
Bosch: F 00M 145 280, F 00M 145 679, F 00M A45 219

Lester Numbers

13986

Unit Numbers

Audi, Volkswagen: 059-903-015Q
BMW: 12-31-7-519-618, 12-31-7-519-620
Bosch: 0 124 515 105, 0 124 625 026

Vehicle Application

BMW Car
325Ci L6 2.5L 2494cc 152cid 2001-2006
325i L6 2.5L 2494cc 152cid 2004-2005
325xi L6 2.5L 2494cc 152cid 2004-2005
330Ci L6 3.0L 2979cc 2001-2006
330i L6 3.0L 2979cc 2004-2005
330xi L6 3.0L 2979cc 2004-2005
330xi L6 3.0L 2996cc 2006
Z4 L6 2.5L 2494cc 152cid 2003-2005
Z4 L6 3.0L 2979cc 2003-2005

BMW - Europe Car
Z4 2200, M54 22 6S1 2003-2005
Z4 2500, M54 25 6S5 2003-2006
Z4 3000, M54 30 6S3 2003-2006
Z4 (E85) Eng.M54 B22 (226S1) 2.2 i 125kW M54 B22 (226S1) 2003-2005
Z4 (E85) Eng.M54 B25 (256S5) 2.5 i 141kW M54 B25 (256S5) 2003-2005
Z4 (E85) Eng.M54 B30 (306S3) 3.0 i 170kW M54 B30 (306S3) 2003-2005

Features & Benefits

• Genuine OEM replacement part
• Manufactured to original factory specifications
• Regulates alternator output voltage
• Helps maintain proper battery charging
• Supports stable charging system performance
• Original fit, function, and electrical characteristics
• Ideal for alternator rebuilding and repair
• Engineered for long-term reliability

What Does a Voltage Regulator Do?

The voltage regulator controls the alternator's output by regulating current supplied to the rotor field winding. As electrical demand changes, the regulator continuously adjusts field current to maintain the proper charging voltage for the battery and the vehicle's electrical system.

A properly functioning voltage regulator helps prevent battery overcharging and undercharging while protecting sensitive electrical components from excessive voltage. Because charging system performance depends on the interaction between the regulator, rotor, stator, rectifier, and battery, replacing a faulty regulator is an important step in restoring alternator performance.

Common Signs Replacement Is Needed

Replace the voltage regulator if you notice:

• Battery overcharging
• Battery not charging
• Low charging voltage
• High charging voltage
• Battery warning light illuminated
• Intermittent charging problems
• Headlights that brighten or dim with engine speed
• Charging system failure during testing
• Voltage regulator failure discovered during alternator rebuilding

Installation Recommendations

Installation should be performed by a qualified technician or experienced alternator rebuilder. Before installing the new regulator, inspect the brushes, brush holder, slip rings, rotor, stator, rectifier, wiring, and electrical connections for signs of wear or damage.

Always verify connector configuration and mounting style before installation. After assembly, bench-test the alternator to confirm proper charging voltage and overall charging system performance.

While You're Rebuilding

Inspect other common wear components to help maximize charging system reliability:

• Bearings
• Brushes
• Brush Holder
• Slip Rings
• Rectifier
• Diodes
• Rotor
• Clutch Pulley
• Insulators

Why Buy From RC Auto Electric?

RC Auto Electric specializes in genuine OEM and premium aftermarket alternator and starter rebuilding components for professional rebuilders, repair shops, automotive technicians, and DIY enthusiasts. Our extensive catalog includes thousands of electrical components backed by accurate cross-reference information to help simplify part identification and reduce ordering mistakes.

Disclaimer

Compatibility information is provided as a reference only. Manufacturing revisions, production changes, and previous rebuilding modifications may affect internal alternator components. Always compare the original OEM part number, connector configuration, mounting style, voltage specifications, cross-reference numbers, and product photographs before installation. If you are unsure about compatibility, contact RC Auto Electric before ordering.