Ignition coils are important parts of a car’s engine, and they can fail over time. If you’re having trouble with your car’s ignition, it’s important to check the ignition coil to see if it’s the cause.
Checking an ignition coil is a relatively simple process that can be done with an ohmmeter. An ohmmeter is a tool that measures electrical resistance. When you connect an ohmmeter to an ignition coil, it will measure the resistance between the primary and secondary windings of the coil. The resistance should be within a certain range, which will vary depending on the make and model of your car. If the resistance is too high or too low, it could indicate that the ignition coil is faulty.
To check an ignition coil with an ohmmeter, follow these steps:
1. Disconnect the negative battery terminal.
2. Remove the ignition coil from the engine.
3. Connect the ohmmeter to the primary windings of the coil.
4. Read the resistance on the ohmmeter.
5. Compare the resistance to the specifications for your car.
6. If the resistance is too high or too low, replace the ignition coil.
Determining Proper Ignition Coil Resistance
Ignition coils are crucial components in the ignition system, transforming low voltage electricity into high voltage to ignite the spark plugs. If the ignition coil fails, it can cause the engine to misfire or even stop running. Therefore, it’s essential to know how to check ignition coil resistance to ensure it’s functioning correctly.
Each type of ignition coil has specific resistance specifications, and deviation from these values indicates potential issues. Consulting the vehicle’s repair manual or examining the coil’s technical data sheet will provide the correct resistance measurements for your specific coil.
It’s important to note that resistance measurements can vary depending on the temperature of the coil. Therefore, it’s recommended to allow the coil to cool before performing the test and compare the readings with the manufacturer’s specifications at the same temperature.
How to Determine Proper Ignition Coil Resistance
1. Disconnect the ignition coil: Locate the ignition coil and disconnect the electrical connector. This step is crucial for safety, as working on an energized coil can result in electrical shock.
2. Set up the ohmmeter: Turn on the ohmmeter and set it to the lowest resistance scale. This will provide the most accurate readings.
3. Touch the probes to the terminals: Hold the ohmmeter’s probes firmly against the terminals on the ignition coil. One probe should be connected to the positive terminal, and the other to the negative terminal.
4. Read the resistance: Observe the ohmmeter’s display to determine the resistance value. Compare this value with the manufacturer’s specifications for your specific coil.
If the measured resistance falls within the specified range, the ignition coil is likely functioning correctly. However, if the resistance is significantly higher or lower than expected, it indicates a potential problem with the coil and further diagnosis is required.
Measuring Primary Resistance Using an Ohmmeter
An ohmmeter is a device used to measure the resistance of an electrical circuit. It can be used to test the ignition coil’s primary resistance, which should be within a specified range for the coil to function correctly. Here’s a detailed guide on how to check the primary resistance of an ignition coil using an ohmmeter:
- Gather the necessary tools: An ohmmeter, a spark plug wire, and a pair of pliers.
- Disconnect the spark plug wire from the ignition coil: Using the pliers, gently pull the spark plug wire from the coil terminal.
- Set the ohmmeter to the correct setting: Most ohmmeters have a dial or switch that allows you to select the resistance range. Set it to the lowest resistance range, typically 0-200 ohms.
- Connect the ohmmeter leads to the ignition coil terminals: Touch one lead of the ohmmeter to the positive terminal (+) of the ignition coil and the other lead to the negative terminal (-).
- Read the ohmmeter display: The ohmmeter display will show the resistance value in ohms. Record this value for comparison with the specified resistance range.
- Repeat the process for other ignition coils (if applicable): If you have multiple ignition coils, repeat steps 2-5 for each coil to check their primary resistance.
Note: The specified primary resistance range for ignition coils varies depending on the make and model of the vehicle. Refer to the vehicle’s service manual for the correct resistance values.
| Symptom | Possible Cause |
|---|---|
| Engine misfires or runs rough | Faulty ignition coil with high or low primary resistance |
| Engine won’t start | Ignition coil with open or extremely high primary resistance |
Interpreting Primary Resistance Readings
The primary resistance reading of an ignition coil provides insight into the condition of its primary winding and the coil’s overall functionality. The reading should be within the specified range provided by the manufacturer. If the resistance falls outside this range, it could indicate issues with the coil.
Too Low Resistance
A primary resistance reading that is significantly below the specified range indicates a short circuit within the primary winding. This could be caused by a damaged insulating material or a short between the primary winding and the core. A shorted primary winding prevents the coil from generating the necessary magnetic field to induce voltage in the secondary winding, rendering it inoperable.
Too High Resistance
Conversely, a primary resistance reading that is significantly above the specified range suggests an open circuit within the primary winding. This could be caused by a broken wire or a damaged connection. When the primary winding is open, no current flows through the coil, which prevents it from generating any voltage in the secondary winding. As a result, the spark plug will not receive the necessary spark to ignite the air-fuel mixture.
Normal Resistance
A primary resistance reading that falls within the specified range indicates that the primary winding is in good condition. In this case, the coil should be able to generate the necessary magnetic field to induce voltage in the secondary winding and provide a spark to the spark plug.
| Resistance Reading | Interpretation |
|---|---|
| Below specified range | Short circuit in primary winding |
| Above specified range | Open circuit in primary winding |
| Within specified range | Primary winding is in good condition |
Checking Secondary Resistance
The secondary resistance of an ignition coil is typically in the range of 5,000 to 15,000 ohms. To measure the secondary resistance, follow these steps:
1. Disconnect the ignition coil from the spark plugs and distributor cap.
2. Set the ohmmeter to the highest resistance scale.
3. Touch one probe of the ohmmeter to the positive terminal of the ignition coil and the other probe to the negative terminal.
4. Read the resistance on the ohmmeter. The resistance should be within the specified range for the ignition coil.
| Resistance | Condition |
|---|---|
| Less than 5,000 ohms | Ignition coil is shorted. Replace the ignition coil. |
| Greater than 15,000 ohms | Ignition coil is open. Replace the ignition coil. |
| Within specified range | Ignition coil is good. |
Understanding Secondary Resistance Specifications
The secondary resistance of an ignition coil is a measure of the resistance encountered by the high-voltage current flowing through the secondary winding. This resistance is typically specified in kilo-ohms (kΩ) and varies depending on the specific ignition coil design and intended application. Generally, higher resistance values result in lower voltage output but increased spark energy, while lower resistance values produce higher voltage output with reduced spark energy.
The specified secondary resistance range for a given ignition coil is typically provided by the manufacturer and should be used as a reference when testing with an ohmmeter. If the measured secondary resistance falls outside of the specified range, it may indicate a problem with the coil that requires further investigation.
| Resistance Range (kΩ) | Spark Energy |
|---|---|
| 0.5 – 1.0 | Very low |
| 1.0 – 2.0 | Low |
| 2.0 – 3.0 | Medium |
| 3.0 – 4.0 | High |
| 4.0 – 5.0 | Very high |
It’s important to note that the specified resistance range may vary between different types of ignition coils and should be referenced from the manufacturer’s specifications for the specific coil being tested.
Identifying Open or Shorted Secondary Windings
To detect an open or shorted secondary winding, you’ll need to measure the resistance across the secondary terminals of the ignition coil. Follow these steps:
1. Set Your Ohmmeter to a High Resistance Scale
Typically, the resistance of a secondary winding ranges from 5,000 to 50,000 ohms. Choose a scale that offers enough range to accommodate these values.
2. Ground the Ohmmeter’s Negative Lead
Connect the negative lead of your ohmmeter to a good ground point on the vehicle’s engine or chassis.
3. Insert the Positive Lead into the Coil Tower
Push the positive lead of your ohmmeter into the center of the coil tower, where the high-tension spark plug wire connects.
4. Read the Resistance Value
Observe the reading on the ohmmeter’s display. The resistance should be within the specified range for the ignition coil. If it reads “OL,” it indicates an open circuit, while a reading close to zero suggests a short circuit.
5. Inspect the Spark Plug Wires
If you suspect an open or shorted secondary winding, check the spark plug wires thoroughly. Look for signs of damage, wear, or loose connections.
6. Compare Measured Resistance to Ignition Coil Specifications
| Ignition Coil Type | Secondary Resistance Range (Ohms) |
|---|---|
| Distributor Ignition Coil | 5,000 – 15,000 |
| Coil-on-Plug Ignition Coil | 7,000 – 25,000 |
| Waste Spark Ignition Coil | 10,000 – 35,000 |
| Electronic Ignition Coil | 12,000 – 40,000 |
| High-Performance Ignition Coil | 15,000 – 50,000 |
Refer to this table to compare your measured resistance values to the specified ranges for different ignition coil types. Deviations from the expected ranges may indicate a faulty ignition coil.
Testing for Continuity
Step 1: Set the Ohmmeter to the Continuity Setting. Locate the continuity setting on your ohmmeter, typically denoted by a musical note or ohm symbol with an arrow through it. Set the dial to this setting.
Step 2: Connect the Ohmmeter to the Ignition Coil Terminals. Touch one probe of the ohmmeter to the “positive” terminal of the ignition coil and the other probe to the “negative” terminal.
Step 3: Observe the Ohmmeter Reading. If the ohmmeter displays a low resistance reading (typically below 1 ohm), it indicates continuity, meaning the electrical circuit between the terminals is complete.
Step 4: Reverse the Ohmmeter Leads. Switch the probes of the ohmmeter (positive to negative, and vice versa) and repeat Steps 2 and 3. The ohmmeter should still display a low resistance reading.
Step 5: Test the Individual Coils. If your ignition coil has multiple coils, test each coil individually by disconnecting them from the spark plugs and repeating Steps 2-4 for each coil.
Step 6: Check for Intermittent Continuity. Gently wiggle or tap the ignition coil while observing the ohmmeter reading. If the reading fluctuates or breaks intermittently, it may indicate a loose connection or damaged insulation.
Step 7: Troubleshooting Intermittent Continuity. If you suspect intermittent continuity, visually inspect the ignition coil for any loose connections or damage. If none is found, use a multimeter to check the voltage supply to the coil. A low voltage supply can cause intermittent continuity issues.
Table: Ohmmeter Readings for Ignition Coil Continuity Testing
| Reading | Interpretation |
|---|---|
| Low resistance (below 1 ohm) | Continuity is present |
| High resistance (above 1 ohm) | Continuity is not present |
| Intermittent reading | Possible loose connection or damaged insulation |
Troubleshooting Ignition Coil Failure
Checking Primary Resistance
Remove the ignition coil from the engine. Disconnect the wires from the coil’s terminals. Connect an ohmmeter to the primary terminals of the coil, which are usually marked with a “+” and a “-“. The normal resistance range for a primary winding is typically between 0.4 and 2 ohms.
Checking Secondary Resistance
Connect the ohmmeter to the secondary terminals of the coil, which are usually located on the top of the coil. The normal resistance range for a secondary winding is typically between 5,000 and 15,000 ohms.
Checking Spark Plug Wires
Inspect the spark plug wires for damage or cracks. Replace any damaged wires.
Checking Distributor Cap and Rotor
Remove the distributor cap and inspect it for cracks or carbon buildup. Clean or replace the cap and rotor if necessary.
Checking Ignition Module
If the ignition coil, spark plug wires, and distributor cap and rotor are all in good condition, the problem may be with the ignition module. Test the ignition module according to the manufacturer’s instructions.
Checking Ignition Switch
Turn the ignition switch to the “on” position and check for power at the ignition coil. If there is no power, the problem may be with the ignition switch.
Checking Battery and Charging System
Make sure that the battery is fully charged and that the charging system is functioning properly. A weak battery or a malfunctioning charging system can cause ignition problems.
Additional Tests
* Spark Test: Disconnect a spark plug wire from a spark plug and hold it close to the engine block. Have someone crank the engine and look for a spark. If there is no spark, the problem may be with the ignition coil, spark plug wire, or distributor.
* Coil Peak Voltage Test: Use a coil peak voltage tester to measure the voltage output of the ignition coil. The peak voltage should be at least 20,000 volts.
| Symptom | Possible Cause |
|---|---|
| Engine misfires or stalls | – Faulty ignition coil – Damaged spark plug wires – Worn distributor cap or rotor – Faulty ignition module – Weak battery or charging system |
Additional Diagnostics for Ignition Coil Malfunctions
If the ohmmeter tests indicate a malfunctioning ignition coil, further diagnostics can help pinpoint the specific issue:
Visual Inspection
Examine the ignition coil for any visible damage, such as cracks, burns, or loose connections. Also, check the wiring harness for any signs of wear or damage.
Spark Test
To perform a spark test, remove the spark plug wire from the ignition coil and hold it close to the engine block while cranking the engine. If a strong spark is present, the ignition coil is likely functioning properly. However, a weak or absent spark may indicate a problem with the ignition coil.
Dwell Test
A dwell test measures the amount of time the ignition coil spends charging. To perform this test, connect a dwell meter to the ignition coil and crank the engine. The dwell time should fall within the manufacturer’s specifications. If the dwell time is too long or too short, it may indicate a problem with the ignition coil.
Substitution Test
If other diagnostic tests are inconclusive, a substitution test can be performed. Borrow a known-good ignition coil and install it on the vehicle. If the engine starts and runs smoothly, the original ignition coil is likely faulty.
Engine Performance Monitoring
Monitor the engine’s performance while driving. If the engine hesitates or misfires under acceleration, it may indicate a problem with the ignition coil. Also, look for any unusual noises or vibrations coming from the engine.
Scan Tool Diagnostics
Some vehicles have on-board diagnostic systems that can detect ignition coil malfunctions. Use a scan tool to retrieve any stored trouble codes that may indicate a problem with the ignition coil.
Ignition Module Test
If the ignition coil is part of an ignition module, test the ignition module as well. The ignition module may be faulty even if the ignition coil checks out okay.
Distributor Cap and Rotor Inspection
If the vehicle has a distributor, inspect the distributor cap and rotor for any cracks, burning, or corrosion. A faulty distributor cap or rotor can prevent the ignition coil from firing properly.
Fuel Pressure Test
Although not directly related to the ignition coil, a low fuel pressure can cause engine misfires that may mimic ignition coil malfunctions. Perform a fuel pressure test to rule out this possibility.
Safety Precautions When Testing Ignition Coils
Before beginning any testing, adhere to these safety precautions to ensure your personal safety and prevent damage to the ignition coil:
1. Wear Protective Gear
Don your safety glasses, gloves, and flame-retardant clothing to protect yourself from potential electrical hazards, burns, and arc flashes.
2. Disconnect Power Source
Locate the battery and disconnect the negative terminal to isolate the ignition system from the power source. Wait for at least 15 minutes for capacitors to discharge.
3. Allow Cooling
Ignition coils can become extremely hot during operation. Before touching them, allow them to cool down sufficiently to prevent burns.
4. Use Insulated Tools
Utilize insulated tools with rubber handles to minimize the risk of electrical shocks. Ensure that the insulation is in good condition before use.
5. Test in a Well-Ventilated Area
Ignition coils can emit potentially harmful gases during testing. Conduct your testing in an open and well-ventilated area to minimize exposure to these fumes.
6. Handle with Care
Avoid dropping or mishandling ignition coils, as they are sensitive and can be easily damaged. Handle them firmly but gently to prevent damage.
7. Avoid Contact with Metal
Keep ignition coils away from any metal surfaces, such as tools or test equipment, to prevent short circuits and electrical hazards.
8. Use Proper Meter Settings
Ensure that your ohmmeter is set to the correct resistance range for testing ignition coils. Refer to the manufacturer’s instructions for specific settings.
9. Test in Series
Connect your ohmmeter in series with the ignition coil. This will provide an accurate reading of the coil’s resistance without introducing any parallel paths.
10. Check for Continuity and Resistance
Perform a continuity check between the primary and secondary terminals. A high resistance or open circuit indicates a faulty ignition coil. The primary resistance should typically fall within 0.5 to 1.5 ohms, while the secondary resistance can range from 5,000 to 25,000 ohms. Refer to the manufacturer’s specifications for specific values.
How to Check Ignition Coil with an Ohm Meter
An ignition coil is a component in a vehicle’s ignition system that converts electrical energy from the battery into high-voltage energy required to create a spark at the spark plugs. A faulty ignition coil can lead to various engine problems, such as difficulty starting, misfiring, or stalling. Using an ohm meter to test the ignition coil can help determine if it is functioning correctly.
Here’s a step-by-step guide on how to check an ignition coil with an ohm meter:
- Disconnect the negative terminal of the battery for safety precautions.
- Locate the ignition coil. It is usually mounted on the top of the engine or near the spark plugs.
- Identify the terminals on the ignition coil. There are typically two terminals: the primary winding terminal and the secondary winding terminal.
- Set your ohm meter to the lowest resistance scale.
- Touch one probe of the ohm meter to the primary winding terminal and the other probe to the secondary winding terminal.
- Read the resistance value displayed on the ohm meter.
People Also Ask
What is a normal resistance reading for an ignition coil?
The normal resistance reading for an ignition coil varies depending on the make and model of the vehicle. Typically, the primary winding should have a resistance of 0.5 to 1.5 ohms, while the secondary winding should have a resistance of 5,000 to 15,000 ohms.
What if the resistance reading is not within the normal range?
If the resistance reading is significantly lower or higher than the normal range, it indicates a faulty ignition coil. A coil with very low resistance may cause a short circuit, while a coil with very high resistance may not generate enough voltage to produce a spark.
Can I check the ignition coil without removing it from the engine?
Yes, it is possible to check the ignition coil without removing it from the engine. However, it may be more difficult to access the terminals and get accurate readings.
