If you’ve noticed problems with your car’s electrical system, testing the electronic voltage regulator can help you determine which part of your car’s electrical system is causing the problem.

Fortunately, testing a voltage regulator is pretty straightforward, but it does require a multimeter.

Note: This test is for cars that don’t have computerized voltage regulation. 

Follow these steps to test your voltage regulator:

Step 1: Set The Multimeter To Voltage

Ensure your multimeter is on the voltage setting.
The voltage setting often looks like ∆V or a V with a few lines above it.

Set it to 20V. Testing an alternator regulator with your multimeter set to Ohm or Amp can damage your device.

Step 2: Connect The Multimeter To Your Battery

To check an alternator regulator, we need to check the battery voltage.

With your car off, connect the multimeter’s black lead to the black (negative) battery terminal and the red lead to the red (positive) battery terminal.

Step 3: Check The Multimeter

The multimeter should be displaying a little over 12 volts with the engine off if your battery is working correctly. If your battery voltage is below  12 volts, it could mean your battery is failing and you may need a replacement soon.

Step 4: Turn Your Vehicle On

With your car in park or neutral and the emergency brake engaged, turn the engine on. Have a look at the multimeter and you should see the reading increase to around 13.8V while the car idles.

If you see 13.8V on your multimeter, you can rule out your car’s alternator as the cause of your electrical issues. 13.8V suggests everything is working correctly and the alternator is charging your battery as it should.

If your output voltage drops below 13V right after starting the engine, you may have a problem with your electrical system. Consider performing a voltage drop test.

Lastly, if you notice a steady or intermittent high or low voltage output, it suggests your alternator voltage regulator is the problem.

Step 5: Rev The Engine

You’ll need an extra set of hands here. Have someone rev the engine while you keep an eye on the multimeter. Slowly build up the car’s revs until it reaches 1,500 – 2,000 RPM.

Step 6: Check The Multimeter Again

If your alternator voltage regulator is working correctly, your battery’s voltage output should cap around 14.5V. If the reading is above 14.5V, you likely have a faulty voltage regulator. If the reading is below 13.8V, your battery is weak and will probably need a replacement.

Now, let’s go over some regulator FAQs:

5 Car Voltage Regulator FAQs

Here are a few common voltage regulator questions and their answers:

1. Where Can I Find The Voltage Regulator?

You can often find the voltage regulator mounted inside or outside of the alternator housing. If it’s mounted outside, you should see a wire harness connecting the regulator to the car’s alternator.

2. Can A Bad Voltage Regulator Ruin A Battery?

Yes, a bad voltage regulator can definitely ruin your car battery.

If too much voltage is flowing to the battery, it can warp the platers and destroy your battery. Alternatively, if there’s low voltage, the battery won’t be able to charge fully and you may struggle to turn your car on.

If the voltage regulator fails completely, the battery power will deep-discharge. While your standard 12 volt lead-acid car battery is supposed to discharge, discharging too far can cause irreversible damage to the plates within the battery, significantly reducing its lifespan.

3. Can I Drive With A Faulty Voltage Regulator?

Technically, you can drive with a faulty voltage regulator, but doing so is risky.

You might be fine and nothing happens, but you run the risk of blowing some expensive electrical components without constant voltage. If you have a faulty voltage regulator, you should have it replaced as soon as possible.

4. How Much Does A Voltage Regulator Cost To Replace?

An alternator voltage regulator replacement is quite an expensive job.

Your car’s make and model will have the greatest impact on the cost of a new voltage regulator. For the part itself, though, you can expect to pay anything between $40 and $140.

However, labor costs also play a big role here.

This is because most voltage regulators sit inside the car’s alternator, making it difficult to access. As a result, labor costs should be somewhere between $140 and $240.

You might pay a little less if you have an external voltage regulator (i.e., your voltage regulator is mounted outside the alternator).

Having said all that, the total cost of replacing a voltage regulator should be somewhere between $180 and $380. Of course, if the faulty regulator damages any other electrical components, the cost will be higher.

5. What Should I Do If I Need A Voltage Regulator Replacement?

If you need a voltage regulator replacement, don’t drive your car to a repair shop as doing so can damage expensive parts.

When looking for a mechanic to perform a replacement, always call for a mechanic to come over and double-check they’re:

• ASE certified
• Offer a service warranty on repairs
• Use only high-quality tools and replacement parts

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