5 Symptoms Of A Bad Distributor Cap and Replacement Cost

While the distributor is not so common in modern cars, they do still exist. Here's how to tell your distributor cap is bad and how much it costs to replace it.

Symptoms Of A Bad Distributor Cap

If you have an older vehicle, it likely runs with a distributor. With a faulty distributor, the car simply doesn’t run as it should, because this vital component supports the motor’s current and connects the plugs to the ignition coil.

I look at some of the symptoms of a bad distributor cap, helping you determine if this is the problem you are dealing with.

This article also touches on where to find the distributor cap and how it functions. In the end, you will know how much it costs to replace a distributor cap if you hope to keep your vehicle running longer. Let’s take a quick look at the possible signs.

Symptoms Of A Bad Distributor Cap

The most common symptom of a bad distributor cap is trouble starting the car during rainy or foggy weather. You may also notice a shaking or stalling engine. Squealing noises are also quite common, and you may also see a check engine warning light on your dashboard.

Here is a more detailed list of the signs of a bad or failing distributor cap to look for:

1. Trouble Starting

Hard Starting

As the distributor cap gets worse, you are going to have trouble starting the engine. You will notice the problem most prominently when the temperatures drop during winter. 

Cold weather cools the cap and can also freeze it. When you attempt to start the engine, the sudden heat can lead to cracks. To avoid this, it’s best to keep your vehicle parked in a garage during colder months. 

2. Shaking

If you are experiencing intense vibrations or shaking in your car, it could be due to the distributor cap causing misfires. The problem might be most prominent when you start the car or when it is shifting gears.

The shaking will feel uncontrollable, and can be felt throughout the entire vehicle. This is a major sign that the distributor cap is faulty. 

3. Stalling

If you can get the car started, but have trouble keeping it going, it could be due to the distributor cap. Inside the distributor, there is a rotor that spins to deliver voltage, and it must be working right to keep the vehicle running.

If there is a clog or crack, it can stop the rotor from spinning. This can cause not only stalling, but backfiring, too. 

4. Squealing Noises

Another sign that the distributor cap is bad is squealing noises from the bearings inside it. This problem creates a unique tell-tale sound that can easily be distinguished from others.

If you check the distributor cap, you might find a build-up of grease, dirt and other pollutants. This blockage of the air circulation is what is causing the squealing sound you hear. 

5. Check Engine Light

Even with an older car, you have a Check Engine Light that alerts you to trouble. However, when this light comes on, it can mean any number of issues.

The best way to tell if the light is on due to the distributor cap is to evaluate the other symptoms. If the Check Engine Light comes on with other symptoms we’ve touched on, you can bet on a faulty cap. 

The function of a Distributor Cap


When the engine starts up, a lot of voltage is produced. This voltage moves into the ignition coil and the electrode of the distributor’s rotor. This part takes the place of the modern ignition system in vehicles.

The rotor in the distributor starts to rotate, allowing power to transfer to the electrodes in the distributor cap. From here, the cap is transferring electricity to the various spark plugs with the help of the wires. 

This process that has been outlined occurs every time the cylinders need a spark to ignite the fuel/air mixture for combustion. Without this part functioning as it should, ignition becomes difficult, if not impossible. 

Distributor Cap Location

Distributor Cap

You can find the distributor cap under the car hood. When you open the hood, you want to search for a black, gray, or red component made from plastic. It is normally near the center of the engine.

Typically, the distributor cap looks like a crown with black or blue cables connected to spokes on the top. These black or blue cables are the spark plug wires, which are needed to transfer power to the plugs.

If you can’t find the distributor cap, you can follow the spark plug wires to see where they attach. You can also check your owner’s manual to help you locate it. If the cap looks cracked or worn out when you find it, you need to replace it.  

Distributor Cap Inspection

Distributor Cap Replacement Cost

The distributor cap replacement cost is $70 to $130 in total for parts and labor. In general, expect to pay about $25 to $60 for the parts, depending on what vehicle you drive. The other $45 to $70 will be the cost of the labor if you need a professional replacement. 

With some simple tools and general know-how, you can replace the distributor cap yourself and save on labor costs. However, you must be careful to label all of the spark plug wires you remove, or you could find yourself with a bigger mess on your hands than you started with. 

Magnus Sellén
Written by:

Magnus is the owner and main author of Mechanicbase. He has been working as a car mechanic for over 10 years, and the majority of them specialized in advanced car diagnostics and troubleshooting. Certified Automotive Diagnostic Technician.

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