How To Test 3 Wire Coil On A Plug With A Multimeter?

In most car models, coil-on-plug (COP) ignition systems are the norm. But testing one for issues can be confusing, so below, I will explain how to test 3 wire coil on a plug with a multimeter.

If you are working on Direct Ignition Systems, you should know how they work, specifically how to test them. As a result, you will be prepared to respond if your ignition system malfunctions. The digital multimeter is one of the most reliable tools for checking the health of your Coil-On-Plug ignition coil.

How To Test 3 Wire Coil On A Plug With A Multimeter:

There are 3 ways to test the 3-wire coil on a plug with a multimeter. One method is the power circuit test, the Second is the ground circuit test, and the third is the triggering signal test.

Power circuit test:

First, check the battery voltage. If it is less than 13V, the vehicle is not running, or the coil pack is not getting power from the PCM. Next, check for power and ground at the coil pack terminals using a suitable test light or multimeter with an amp setting. If the power and ground circuits are not identified with a colored wire. Then use a test light to identify each wire. Finally, check the correct power level and ground at the coil pack. For most cars, this should be more than 10V on each wire with the key on or the engine running.

Ground circuit test:

To perform this test, locate the coil pack’s primary ground terminal. This ground terminal can be identified by looking at the plug connectors, which are often connected to a black wire. Once you have located the coil pack’s primary ground terminal, begin testing for ground using a multimeter or test light. If you are using a multimeter, set it to ohms. If the reading on your multimeter is lower than 10 ohms, then the ground circuit is suitable. Although, you should continue testing the triggering signal.

Triggering signal test:

To perform this test, you will need to locate the coil pack’s trigger terminal. This trigger terminal is often identified with a gray wire and can be found on the side of the coil pack. Once you have located the trigger terminal, begin testing for a triggering signal using a multimeter. If the reading on your multimeter is lower than 5V or 10kHz. Then the triggering sign is either missing or faulty, and you should replace the coil pack.

If your 3-wire coil-on plug is testing as healthy. Then you can rest assured that your ignition system is functioning correctly and move on to other areas of car maintenance and repair. However, if your coil pack shows any signs of wear or malfunction. It is essential to replace it as soon as possible to avoid further issues. Whether you are working on a DIY project or taking your car in for professional repair. However, knowing how to test the coil pack is essential for ensuring that your ignition system is working correctly.

Symptoms of a bad ignition coil

Following are the symptoms of a bad ignition coil if not working correctly.

Power reduction:

A bad ignition coil will reduce the power to the spark plugs, leading to a loss of power and reduced efficiency.

Reduced fuel economy:

A faulty ignition coil can also lead to decreased fuel economy and performance.

Surging or misfiring:

If the ignition coil is not functioning correctly, you may experience surging or misfiring when accelerating.


If the coil pack is faulty, you may also hear a rattling or buzzing noise from the engine.

If you are experiencing any of these symptoms, having your ignition coil checked as soon as possible is crucial to avoid more severe issues down the road. With the help of a multimeter, you can quickly and easily test your coil pack and determine if it is functioning correctly or needs replacement.

What are the three wires on the ignition coil?

An ignition coil, also known as an induction coil or spark coil, is a type of transformer that converts the low voltage of a battery into the high voltage needed to create an electric spark in the spark plug of an internal combustion engine. The three wires found on an ignition coil are typically referred to as the primary winding wire, secondary winding wire, and ground wire.

Primary winding wire:

The primary winding wire carries electrical current from your car’s battery or another electrical source to the ignition module. This current will travel through this direct winding wire, which creates a magnetic field within the core of your ignition coils. This magnetic field builds up until it becomes strong enough to break through its insulation, causing a short circuit across two output terminals (anode and cathode). This process causes what is called “induction,” – wherein electricity flows from one point (the primary windings) to another (the secondary windings). 

Secondary winding wire:

The second or “secondary” winding is connected between those Coil Output Terminals and consists of hundreds of turns (usually 800-100 turns)of excellent copper. It insulated with varnish insulation around all sides except where it connects with terminal screws. As electricity flows between those two terminals – creating sparks along its path – these secondary windings further amplify them by tens. If not hundred times more than their original strength at points where they jump out towards plugs resulting in higher level amplifications. The greater spark intensity enabling greater ignitions efficiency thus improving overall performance for engines. 

Ground Wire:

The third “Ground” Wire works as the ground connection for all other components. So every component can work correctly without any faults in general, such as misfires due to engine vibrations, etc. Ensuring proper operation at all times with batteries maintaining balanced charging/discharging cycles maintaining good State Of Health(SOH) status indefinitely.

Wrapping Up:

Here we discussed how to test 3 wire coil on a plug with a multimeter, including the function of each wire and what to look out for when trying your ignition coil. Whether you are a professional repair technician or just performing routine maintenance on your vehicle. It is essential to be familiar with your car’s ignition system’s critical components to ensure optimal performance and safety.