Genuine VW/Audi 03L903803C Voltage Regulator – Audi, VW | 059903803M VW03L903803C

• 059903803M
• VW03L903803C

Voltage regulators maintain a constant range of alternator voltage output and convert the alternate current (AC) produced by the alternator into the direct current (DC) the vehicle operates on. As the alternator turns, it uses coil windings and magnets to create the alternate current. The faster the alternator turns, the more current and voltage is produced. The voltage regulator uses diodes to convert the AC to DC, limiting the alternator’s voltage output to 12-14 volts.

Voltage regulators fail when they can no longer convert alternate current to direct current or when they can no longer maintain a consistent voltage that the vehicle requires to operate.

Signs of a faulty voltage regulator include:

• Surging lights
• Flickering interior lights
• Instrument cluster or panel malfunctioning
• Battery light or check engine light illuminated
• A battery not being charged

Checking battery voltage or alternator output are simple ways to test a voltage regulator. Fluctuating battery voltage or drops in alternator output when the engine is at idle indicates the voltage regulator has failed and is not regulating voltage or not converting alternate current to direct current.

Replacing Your Vehicle’s Voltage Regulator

Some voltage regulators are external to the alternator and can be removed and replaced in series with the alternator output circuit. Other voltage regulators are mounted inside of the alternator and may be removable and replaceable, but some will require the replacement of the alternator to replace the voltage regulator.

Genuine VW/Audi Voltage Regulators.