An ignition coil is a critical component in an internal combustion engine’s ignition system, responsible for converting low-voltage current from the battery into high-voltage electricity necessary to create a spark at the spark plugs. A faulty ignition coil can lead to a range of engine problems, including misfiring, rough idling, and difficulty starting.
Testing an ignition coil with a multimeter is a straightforward process that can help you determine if the coil is malfunctioning. Before you begin, ensure you have a multimeter set to the appropriate resistance setting and follow safety precautions such as wearing gloves and eye protection. Start by disconnecting the negative terminal of the battery to prevent electrical shock. Then, locate the ignition coil, typically situated near the engine’s distributor or spark plugs.
Once you have identified the ignition coil, follow these steps:
1. Disconnect the electrical connectors from the ignition coil.
2. Set your multimeter to the resistance setting (usually denoted by the Greek letter “Omega”).
3. Touch one probe of the multimeter to the positive terminal of the ignition coil and the other probe to the negative terminal.
4. The multimeter should display a reading within the specified range for your particular ignition coil (refer to the manufacturer’s specifications).
5. If the multimeter reading is significantly lower or higher than the specified range, the ignition coil may be faulty and should be replaced.
Introduction to Ignition Coils
Ignition coils are crucial components in an internal combustion engine’s ignition system. They transform the vehicle’s low-voltage electrical current into high voltage, enabling the spark plugs to ignite the air-fuel mixture in the engine’s cylinders. Ignition coils consist of a primary winding and a secondary winding, typically wrapped around an iron core. The primary winding is connected to the vehicle’s battery, while the secondary winding is connected to the spark plugs. When a signal is sent from the ignition module, the primary winding becomes energized and creates a magnetic field within the coil. The collapsing magnetic field induces a high voltage in the secondary winding, which then travels to the spark plugs, creating the spark necessary for combustion.
Ignition coils can fail over time due to various factors such as heat, vibration, or electrical overload. A faulty ignition coil can lead to difficulty starting the engine, misfires, reduced engine power, and poor fuel economy. Therefore, it is essential to check the condition of the ignition coils periodically to ensure proper engine performance.
Types of Ignition Coils
| Type | Description |
|---|---|
| Conventional Ignition Coils | Single ignition coil serves multiple cylinders |
| Coil-on-Plug (COP) Ignition Coils | Separate ignition coil for each cylinder, mounted directly on the spark plug |
| Coil-Near-Plug (CNP) Ignition Coils | Ignition coil located near the spark plug, but not directly mounted on it |
Troubleshooting Ignition Issues
Ignition issues can be frustrating, especially when you’re in a hurry or far from home. There are several potential causes of ignition problems, including faulty spark plugs, ignition coils, or electrical issues. One way to test your ignition coil is with a multimeter.
**Note:** Always refer to your vehicle’s service manual for specific instructions when troubleshooting ignition issues.
Testing the Ignition Coil with a Multimeter
1. Gather Your Tools and Identify the Ignition Coil
You’ll need a multimeter, a wrench or socket set, and a spark plug tester. Locate the ignition coil, which is usually located near the engine’s distributor cap or spark plugs.
2. Testing the Ignition Coil’s Primary Circuit
Warning: Disconnect the negative battery terminal before proceeding.
- Set the multimeter to its ohms (Ω) setting, which measures resistance.
- Disconnect the wiring harness connector from the ignition coil.
- Connect one multimeter lead to the positive (+) terminal of the ignition coil and the other lead to the negative (-) terminal.
- The multimeter should display a resistance reading between 0.5 and 2.0 ohms. If the reading is significantly higher or lower, the ignition coil may be faulty.
3. Testing the Ignition Coil’s Secondary Circuit
- Set the multimeter to its volts (V) setting, which measures voltage.
- Reconnect the wiring harness connector to the ignition coil.
- Connect one multimeter lead to the center terminal of the ignition coil and the other lead to a ground point on the engine.
- Have an assistant crank the engine while you observe the multimeter. You should see a voltage reading of several thousand volts. If the reading is significantly lower, the ignition coil may be faulty.
- Normal: Resistance falls within the specified range, indicating a functional primary winding.
- Too Low: Resistance is significantly lower than the specified range, indicating a short circuit in the primary winding.
- Too High: Resistance is significantly higher than the specified range, indicating an open circuit in the primary winding.
- Intermittent: The resistance reading fluctuates, indicating a loose connection or damaged primary winding.
- Open circuit in the primary or secondary winding.
- Shorted turns in the primary or secondary winding.
- Damaged insulation between the primary and secondary windings.
- Worn or damaged contacts in the distributor cap or rotor.
- Disconnect the vehicle’s battery: Before any testing, disconnect the negative terminal of the battery to prevent any electrical shocks or shorts.
- Wear appropriate gear: Insulated gloves and safety glasses should be worn throughout the process to protect against potential sparks or debris.
- Use caution around high voltages: Ignition coils handle high voltages. Avoid touching the terminals directly and use insulated tools to prevent electric shocks.
- Do not perform tests on a running engine: Working on a running engine can be dangerous. Always shut off the engine and allow it to cool before beginning testing.
- Check for cracks or damage: Before connecting the multimeter, visually inspect the coil for visible cracks or damage to the housing or terminals.
- Ensure proper ventilation: Ignition coil testing might release fumes or vapors. Ensure there is adequate ventilation in the work area to avoid inhalation of these substances.
- Avoid contact with hot surfaces: Ignition coils can become hot during operation. Allow them to cool down before handling.
- Use a multimeter with an appropriate range: Select a multimeter with a voltage range capable of measuring the high voltages present in ignition coils.
- Ground the test equipment: Connect the multimeter’s ground lead to a reliable ground point on the vehicle’s chassis to ensure accurate readings.
- Follow all manufacturer’s instructions carefully: Refer to the specific vehicle’s repair manual or the ignition coil manufacturer’s guidelines for correct testing procedures and precautions.
- Set the multimeter to the ohms setting.
- Connect the positive lead of the multimeter to the positive terminal of the ignition coil.
- Connect the negative lead of the multimeter to the negative terminal of the ignition coil.
- Read the display on the multimeter.
- Engine misfires
- Difficulty starting the engine
- Reduced engine power
- Poor fuel economy
4. Interpreting the Results
If the ignition coil fails either of these tests, it is likely faulty and should be replaced. Before replacing the ignition coil, ensure that any other potential causes of the ignition issues, such as spark plugs or electrical connections, have been ruled out.
| Test | Normal Reading | Possible Issue if Reading is Abnormal |
|---|---|---|
| Primary Circuit Resistance | 0.5 to 2.0 ohms | Faulty ignition coil |
| Secondary Circuit Voltage | Several thousand volts | Faulty ignition coil, spark plug, or electrical connection |
Identifying a Faulty Ignition Coil
Identifying a faulty ignition coil can be crucial for maintaining a smooth-running engine. Here are a few symptoms that may indicate a problem with the ignition coil:
Misfiring and Rough Idling
Ignition coil problems can lead to misfiring, causing the engine to run roughly or sputter. This is because a faulty coil may not deliver the necessary voltage to the spark plug, resulting in incomplete combustion and reduced engine performance.
Difficulty Starting
A failing ignition coil can make it difficult to start the engine. When the coil is unable to generate a strong enough spark, the engine may struggle to turn over or may not start at all. This is particularly noticeable during cold starts, when the engine requires more voltage to ignite.
Reduced Engine Power
If the ignition coils are not functioning properly, the engine may experience reduced power and acceleration. This is because the lack of a strong spark can lead to inefficient combustion, resulting in lower engine output and performance.
Backfiring
In some cases, a faulty ignition coil can cause backfiring, which occurs when the air-fuel mixture in the cylinder ignites prematurely. This can be due to a weak spark or improper timing, resulting in a loud popping sound from the exhaust system.
Illuminated Check Engine Light
Many modern vehicles are equipped with an engine control module (ECM) that monitors engine performance. When the ECM detects a problem with the ignition coil, it may illuminate the check engine light on the dashboard, indicating the need for further diagnosis.
Checking for Spark
To test for spark, follow these steps:
| Step | Action |
|---|---|
| 1 | Locate the ignition coil. |
| 2 | Disconnect the spark plug wire from the spark plug. |
| 3 | Connect a spark tester to the spark plug wire. |
| 4 | Ground the spark tester to the engine block. |
| 5 | Start the engine and observe the spark tester. |
If the spark tester generates a strong, blue spark, the ignition coil is likely functioning correctly. However, if the spark is weak or intermittent, the ignition coil may be faulty and require replacement.
Multimeter Basics for Coil Testing
What is a Multimeter?
A multimeter is a versatile electrical testing tool that combines the capabilities of a voltmeter, ammeter, and ohmmeter. It allows for a wide range of electrical measurements, including voltage, current, and resistance.
Multimeter Modes
Multimeters typically offer three main modes of operation: voltage measurement, current measurement, and resistance measurement. Each mode requires a specific set of test leads and connection points on the multimeter.
Measuring Resistance with a Multimeter
To measure resistance with a multimeter, set it to the ohms (Ω) mode. Connect the positive test lead to one end of the coil and the negative test lead to the other end. The multimeter will display the resistance value in ohms.
Interpreting Resistance Readings for Ignition Coils
The resistance of a good ignition coil typically falls within a specific range. Most primary coil windings range from 0.4 to 2 ohms, while secondary coil windings range from 5,000 to 20,000 ohms. Deviations from these ranges may indicate a problem with the coil.
| Coil Type | Resistance Range |
|---|---|
| Primary Winding | 0.4 – 2 Ω |
| Secondary Winding | 5,000 – 20,000 Ω |
Testing Primary Resistance
To test the ignition coil’s primary resistance, follow these steps:
1. Set Multimeter to Resistance Mode
Switch your multimeter to the ohms (Ω) scale, typically ranging from 200 ohms to 20k ohms.
2. Identify Ignition Coil Terminals
Locate the two terminals on the ignition coil, typically labeled “+” and “-“. These terminals are where the power supply and ignition switch connect.
3. Touch Probes to Terminals
Touching the multimeter probes to the terminals, ensure a proper connection. The display will show the resistance value between the two terminals.
4. Compare to Specification
Check your ignition coil’s specifications for the expected primary resistance range. Compare this range to the resistance value obtained from the multimeter.
5. Analyze Results
| Primary Resistance Measurement | Indication |
|---|---|
| Within Specification | Functional Primary Winding |
| Significantly Lower | Short Circuit |
| Significantly Higher | Open Circuit |
| Fluctuates | Loose Connection or Damaged Winding |
Measuring Secondary Resistance
The secondary resistance of an ignition coil is the resistance of the secondary winding. This winding is responsible for creating the high voltage that is required to jump the spark plug gap. The secondary resistance can be measured using a multimeter.
Step 1: Set the multimeter to the ohms setting.
Step 2: Connect the black lead of the multimeter to the negative terminal of the ignition coil.
Step 3: Connect the red lead of the multimeter to the positive terminal of the ignition coil.
Step 4: Read the display on the multimeter. The reading should be between 0.5 and 1.0 ohms.
Step 5: If the reading is not between 0.5 and 1.0 ohms, the ignition coil may be damaged and should be replaced.
Step 6: Check the resistance of the secondary winding by connecting one probe of the multimeter to the positive terminal of the coil and the other probe to the negative terminal of the coil. The resistance should be between 0.5 and 1.0 ohms. If it is not, the coil is bad and should be replaced.
| Possible causes of ignition coil failure |
|---|
|
|
Checking Spark Output
To check the spark output of the ignition coil, follow these steps:
1. Disconnect the spark plug wire from the spark plug.
2. Connect the black lead of the multimeter to the metal body of the spark plug.
3. Connect the red lead of the multimeter to the tip of the spark plug wire.
4. Start the engine and observe the multimeter reading.
| Reading | Result |
|---|---|
| 0 V | No spark |
| 12 V | Spark present |
5. If there is no spark, repeat steps 2-4 with the spark plug wire connected to a different spark plug.
6. If there is still no spark, the ignition coil is likely faulty and should be replaced.
7. To further test the ignition coil’s ability to produce a strong spark, you can use a spark tester. A spark tester is a device that creates a controlled spark between two electrodes. Connect the ignition coil’s output wire to the spark tester, then start the engine and observe the spark. A weak or intermittent spark indicates a faulty ignition coil.
Interpreting Test Results
1. Primary Resistance Reading
An acceptable reading for primary resistance is typically between 0.4 and 2 ohms. Anything significantly higher could indicate a break in the coil.
2. Secondary Resistance Reading
Expected secondary resistance values vary depending on the ignition coil type. Consult a service manual for specific ranges.
3. Primary Continuity
Continuity between terminals 1 and 15 should exist. No continuity indicates an open circuit.
4. Secondary Continuity
Continuity should be measured between the central terminal and the spark plug wire terminal. No continuity points to an open circuit.
5. Primary Ground Insulation
An infinite resistance (no continuity) between terminals 1 and 15 and the coil body indicates proper insulation.
6. Secondary Ground Insulation
Similarly, infinite resistance between the central terminal and the coil body ensures proper insulation.
7. Spark Plug Wire Terminal
Continuity between the spark plug wire terminal and the coil body should be absent. Its presence indicates a short circuit.
8. Dwell or Duty Cycle Test
This test measures the time the ignition coil spends charging and discharging. A fully functional coil will have a dwell time within manufacturer specifications.
Dwell Time Troubleshooting Guide
| Dwell Time Reading | Possible Issue |
|---|---|
| Extremely Short | Coil primary circuit short |
| Extremely Long | Coil primary circuit open |
| Intermittent | Loose or faulty connections |
An oscilloscope can provide a more precise measurement of dwell time and duty cycle.
Safety Precautions for Coil Testing
Inspecting ignition coils is a common troubleshooting procedure, but to ensure your safety, it’s imperative to follow these precautions:
Troubleshooting Primary Circuit Problems
1. Check for power at the ignition coil’s positive terminal. Use the multimeter set to DC volts. Connect the black probe to the negative battery terminal and the red probe to the positive terminal of the ignition coil. You should see a reading of 12 volts.
2. If there is no power at the positive terminal, check the fuses in the fuse box. Replace any blown fuses.
3. Check for continuity in the primary circuit. Set the multimeter to ohms. Connect the black probe to the negative terminal of the battery and the red probe to the positive terminal of the ignition coil. You should see a reading of 0 ohms.
4. If there is no continuity in the primary circuit, check the wiring harness for any breaks or shorts.
Troubleshooting Secondary Circuit Problems
5. Check for spark at the spark plugs. Remove the spark plug wires and insert a spark plug into each wire. Hold the spark plug against the cylinder head and crank the engine. You should see a spark jump from the spark plug to the cylinder head.
6. If there is no spark at the spark plugs, check the ignition coil’s secondary circuit. Set the multimeter to ohms. Connect the black probe to the negative terminal of the coil and the red probe to the positive terminal of the coil. You should see a reading of 5,000 to 10,000 ohms.
7. If the secondary circuit is open, replace the ignition coil.
8. Check for a short to ground in the secondary circuit. Set the multimeter to ohms. Connect the black probe to the negative terminal of the coil and the red probe to the metal body of the car. You should see a reading of infinity.
9. If there is a short to ground in the secondary circuit, check the wiring harness for any shorts.
10. Check the ignition module. The ignition module controls the ignition coil. If the ignition module is faulty, it can cause the ignition coil to fail. To test the ignition module, you will need a scan tool. Connect the scan tool to the car’s diagnostic port and follow the on-screen instructions to test the ignition module.
How To Test A Ignition Coil With Multimeter
An ignition coil is a component of an internal combustion engine that provides the high voltage necessary to create an electric spark in the spark plugs. A multimeter is a device that can measure electrical properties such as voltage, current, and resistance. By using a multimeter, you can test an ignition coil to determine if it is functioning properly.
To test an ignition coil with a multimeter, follow these steps:
The resistance of a good ignition coil will typically be between 0.5 and 5 ohms. If the resistance is too low, the ignition coil may be shorted. If the resistance is too high, the ignition coil may be open.
People Also Ask About How To Test A Ignition Coil With Multimeter
Can you test an ignition coil without removing it?
Yes, you can test an ignition coil without removing it. To do this, you will need to use a multimeter to measure the resistance of the coil. The resistance of a good ignition coil will typically be between 0.5 and 5 ohms.
What are the symptoms of a bad ignition coil?
The symptoms of a bad ignition coil can include:
How much does it cost to replace an ignition coil?
The cost to replace an ignition coil can vary depending on the make and model of your vehicle. However, you can expect to pay between $50 and $200 for a new ignition coil.
