How to Test 4 Wire Coil on Plug With Multimeter

How to Test 4 Wire Coil on Plug With Multimeter

Coil on plug (COP) ignition systems are commonly used in modern vehicles to provide a more efficient and reliable spark to the engine. Each coil on plug unit consists of a coil pack and a spark plug wire, making it easy to diagnose and test individually. In this article, we will guide you through the process of testing a 4 wire coil on plug using a multimeter.

Before we begin, it’s important to note that a multimeter is an essential tool for this task. Make sure you have a digital multimeter with the ability to measure resistance and voltage. Additionally, consult your vehicle’s repair manual for specific instructions and specifications.

Step 1: Preparation
Start by opening the hood of your vehicle and locating the coil on plug units. These are usually mounted on top of the engine, directly above the spark plugs. Remove any plastic covers or components that may be obstructing access to the coil packs.

Step 2: Disconnecting the Coil on Plug Unit
To isolate the coil on plug unit, you need to disconnect it from the wiring harness. Gently remove the electrical connector by pressing the release tab and pulling it apart. Be cautious not to damage the connector or the wiring.

Step 3: Testing for Resistance
Set your multimeter to the resistance (ohms) mode. Connect the positive lead to the coil’s primary winding terminal and the negative lead to the case or any metal part of the coil. A good coil should have a resistance reading within the specified range mentioned in your vehicle’s repair manual. If the resistance is significantly higher or lower, the coil may be faulty and require replacement.

See also  How to Test Spark Plug Wires Without Multimeter

Step 4: Testing for Voltage
Set your multimeter to the voltage (volts) mode. Reconnect the electrical connector to the coil and start the engine. Be cautious of moving parts and the high voltage present in the ignition system. Carefully probe the positive and negative terminals of the coil with the multimeter leads. You should see a voltage reading within the specified range mentioned in your vehicle’s repair manual. If there is no voltage or an abnormal voltage reading, the coil may be faulty.

Step 5: Repeating the Process
Repeat steps 3 and 4 for each coil on plug unit in your vehicle. Remember to disconnect and reconnect the electrical connector each time to ensure accurate readings.


Q: Why should I test my 4 wire coil on plug?
A: Testing the coil on plug units is essential to diagnose ignition system problems, such as misfires, rough idle, or lack of power. It helps identify faulty coils and prevents unnecessary replacement of other components.

Q: What are the symptoms of a faulty coil on plug?
A: A faulty coil on plug can cause engine misfires, rough running, hesitation, or a complete failure to start. These symptoms are often accompanied by a check engine light or diagnostic trouble codes related to the ignition system.

Q: Can I test the coil on plug without a multimeter?
A: While it is possible to test the coil on plug without a multimeter, using a multimeter provides more accurate and reliable results. It is highly recommended to use a multimeter for precise testing.

Q: Can a faulty coil on plug damage other engine components?
A: Yes, a faulty coil on plug can cause damage to other engine components, such as the catalytic converter, oxygen sensors, or spark plugs. It is crucial to diagnose and replace faulty coils promptly to prevent further damage.

See also  Where to Buy Posi Tap Wire Connectors

In conclusion, testing a 4 wire coil on plug with a multimeter is a straightforward process that can help diagnose ignition system issues. By following the steps outlined in this article and referring to your vehicle’s repair manual, you can effectively identify faulty coils and ensure the optimal performance of your vehicle’s engine.