How to Test a CDI Box with a Multimeter: A Step-by-Step Guide

Of all the component parts of a motorbike, there is one that is most important for the bike's proper functioning. That is the CDI or black box, a part essentially functions as the heart of the motorbike or any other device or vehicle it is a part of. You can find the CDI box on mopeds, scooters, lawnmowers, chainsaws, motors, motorcycles, etc.

Even though the CDI box is always built with high-quality materials, it can sometimes suffer damage. It can be the box case or one of the parts that become damaged and cause problems with the motorcycle's ignition system. If that ever happens to you, you should know how to test the CDI box and determine whether the problem comes from within the box or some other part.

In today's guide, I will tell you what the CDI box is, how it functions, and how to test it using a multimeter if you suspect it is faulty. If you want to learn more about these topics, stick around for the rest of the guide!

What is a CDI Box?

So, I mentioned in the introduction that the CDI box is one of the most critical parts of a motorcycle, and that is true. You need the CDI box to turn on the ignition system and drive the bike. Without you, you cannot turn on the motorcycle or drive it.

CDI stands for capacitive discharge ignition system. It comes in its own box, located under the motorcycle's seat. It is usually connected to the bike stator with a blue and white wire. If you want the CDI to function properly, you must always ensure it stays connected to the stator.

Usually, problems with the CDI box are challenging to diagnose as there are quite a few parts in the box that could be causing the faulty CDI box. You might be dealing with a worn-out ignition coil, a dead cylinder, or even a bad diode, causing unusual motorcycle behavior.

How does the CDI box work?

To turn on your motorcycle, you use a key. When you turn the key, the excitor coil will notify the ignition system to start working. So, the coil will get voltage induced into it, which will cause the capacitor to fill up. A trigger mechanism causes the capacitor to discharge as soon as it fills up.

The capacitor discharge ignition is the part that sends the voltage from the excitor coil to the ignition coil. The electrical current moving through the contacts of the spark plug help start the bike ignition.

This may sound strange to people who have never dealt with bike parts. The only thing worth noting is that those not professional at working with bike parts are better off consulting a professional mechanic. That way, they ensure their motorbike gets the proper repairs, with all faulty parts replaced.


How to know if you have a bad CDI box?

If your motorbike is acting differently than usual, it could be because of a faulty CDI box. If your bike has a bad CDI, it will have problems such as a backfiring or misfiring engine or even engine stalling.

Should you suspect a problem with the capacitor discharge ignition system, you can do a few tests to find out what is causing the issues. More on that in the following section!

How to Test a CDI Box with a Multimeter [Step-By-Step Guide]

cdi box

There are many ways to test the CDI box, although I have found that using a multimeter is the easiest. Suppose you need to learn what the multimeter is. In that case, it is a device that can measure voltage, resistance, or electrical current going through any piece of electrical equipment. It has two probes that you attach to the part you are testing.

I recommend the multimeter instead of any other piece of equipment because it is effortless and inexpensive, so anyone can use it. There are analog and digital multimeters, which are more convenient because of the detailed information it gives.

If you decide to perform the CDI box tests with a multimeter, follow these five straightforward steps to get accurate results. Here is what to do:

Step 1 - Safety Measures

The first and most important thing is to stay safe while performing the tests. You must turn off the ignition and give the motorbike at least half an hour to cool down. Otherwise, it would be more challenging to perform the tests.

At the same time, I recommend wearing protective eyewear and waterproof and cut-resistant hand gloves. At this point, you can also check whether you have all the needed equipment: your bike and the multimeter with the two probes. If you have everything, you can move on to the next step.

Step 2 - CDI Box Removal

The second step would be to remove the CDI box to perform the first test, called the cold test. The position of the CDI box could vary depending on the vehicle or device you are testing. Still, when it comes to bikes, it is usually located under the bike seat.

So, go ahead and look for it there. When you find it, you will see two blue and white wires going from the CDI box to the stator. You need to disconnect the two pin connectors and free the CDI box.

After doing this, you can remove the CDI from the bike and leave it to rest for 30 to 60 minutes. During this time, you allow the capacitor discharge ignition to discharge, making the part safer for you to work with.

It is also wise to do a quick visual inspection just to see if there are any abnormalities on the CDI ignition battery or the box itself. If you can see damage on the CDI box, you can replace it immediately. But if there is no visible damage, you can start testing the CDI box.

Step 3 - Cold Test

The first test I recommend you do is the cold test. For this test, you will need the CDI box and the multimeter. After removing the CDI box from the motorbike, you should find two spots to connect the multimeter probes. They should be on the front side of the CDI box, and they can be in different sizes.

So, grab your multimeter and set it to continuity mode by turning the knob. Then, connect the multimeter probes to the CDI box and do the test. If you have a bad CDI, the multimeter will start making a beeping sound. If it is okay, you will not hear anything.

The beeping sounds indicates that something is wrong with the CDI box. It could be a dead cylinder, faulty capacitor, or diode problem. Whatever it is, you need to repair it or replace the CDI box with a brand-new CDI box.

Step 4- Hot Test

The second test you can try doing is the hot test, where you need both the CDI box and the stator end. Again, you will be using a multimeter to do the test.

This test is more complicated than the previous one, as you deal with several wires. Namely, while the CDI box is still connected to the stator, you should connect the wires. The white wire will serve as the ground wire and go into the ground, whereas the blue wire will be connected to the white wire.

After setting this up, you should set the multimeter to ohms for testing resistance and connect it to the CDI box. You should get 77 to 85 ohms reading on the blue-to-white wire connection, whereas the white-wire-to-ground link should have resistance between 360 and 490 ohms.

If the tests show that the resistance is within these limits, the CDI box functions properly. If it goes above or below the limits, there is a problem with the CDI system, and you should have a qualified mechanic look at it as soon as possible.

With CDI boxes, replacing them is always better than repairing them. So, try to install new CDI boxes instead of the faulty ones as soon as possible.


Thank you for reading this detailed guide on the CDI box you can find on motorbikes and how to test it using a multimeter. I hope you know how to perform the cold and hot test on your CDI box and the visual inspection mentioned above.

Remember that working with such essential bike parts should not be taken lightly. If you do not have experience with CDI box testing or repairs, consider taking your bike to a professional mechanic who will tell you whether it works properly. A faulty CDI unit should be replaced immediately to bring your bike back to its former glory.

If you have experience with faulty CDI boxes, let us know your tip testing tips and tricks in the comments below. I cannot wait to read all about it!

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