How to Check for a Bad Voltage Regulator

Updated February 21, 2017

The voltage regulator in your vehicle, although one of the smallest components in your engine compartment, serves as a major vehicle safety feature. Your automobile's electronics and battery depend upon even, steady voltage and current for proper operation. When your car begins to show signs of running rough, electronics malfunctioning or headlights alternate between bright and dim at night, it is essential that you test the voltage regulator as soon as possible to prevent permanent damage to components in the vehicle.

Consult an automobile manual for your year, make and model of vehicle and turn to the section that details your vehicle's electrical system. Look up the location of the voltage regulator, which is normally found near the battery in the engine compartment.

Plug in the multimeter probe wires into the meter, plugging the black wire plug into the negative (-) jack and the red wire plug into the positive (+) jack.

Activate your vehicle's parking brake, if it has one, and start the vehicle. Allow the vehicle to warm up and to settle into an even idle.

Open the engine compartment bonnet of your vehicle and locate the voltage regulator per the diagrams in your chosen automotive repair manual. The regulator will have several wires coming off it, and you are looking for the black (negative) and red (positive) wires for testing purposes. Turn the meter on to measure volts and carefully touch the black probe to the negative terminal of the voltage regulator and then touch the red probe to the positive terminal. If the wires are identical in colour, or there are no polarity markings, it is of no concern as the multimeter will simply display a minus sign (-) if you have the probes reversed, and this can be safely ignored in this test.

Watch the voltage display on the LCD of your multimeter. The voltage should remain constant without much fluctuation, although you will notice the numbers varying slightly. If the voltage coming from the regulator falls between 13 and 14 volts, the regulator is functioning properly. However, if you notice the voltage falls below 12 volts or rises erratically above 14 volts, sometimes going as low as 8 volts or as high as 18 volts, turn the car off immediately and replace your regulator, as it is faulty.


If you smell something akin to burning match heads (sulphur), use extreme caution when working around the battery. This smell is the result of the battery overheating, which is a good indication that your voltage regulator is permitting a state of overcharging the battery. If the smell is strong, turn the car off and allow the battery to cool for several hours, as there is a serious risk of the battery exploding, which may cause serious injury or death.

Things You'll Need

  • Manual for your automobile (Haynes, Chilton, factory)
  • Electronics multimeter
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About the Author

Kurt Schanaman has had several editorials printed by the Star-Herald Newspaper publication in Western Nebraska. He attended Western Nebraska Community College.