How to Verify if Your Car’s Ignition Coil Has Power

When it comes to troubleshooting car issues, verifying the power to the ignition coil is essential. This article will guide you through various methods to check if your car’s ignition coil has power, whether you have modern coil on plugs or an older coil system. Proper maintenance can significantly enhance your vehicle's performance and prevent costly repairs.

1. Understanding the Importance of Testing the Ignition Coil

Testing your car's ignition coil is crucial for ensuring optimal engine performance. The ignition coil boosts the voltage from the battery to the spark plug, which in turn ignites the fuel and air mixture in the engine. Without the proper voltage, the engine may misfire, leading to poor performance, reduced fuel efficiency, and even engine damage.

2. Measuring Voltage with a Voltmeter

The simplest way to check if your car’s ignition coil has power is to use a voltmeter. Here’s how you can do it:

1. Older Car with a Coil: If you have an older car with a standalone coil, locate the power supply wire for the ignition coil. Turn the ignition switch to the on position and measure the voltage across this wire. If there’s no voltage, there might be an issue with the power supply or the ignition coil itself.

2. Gentle Brush Test: As an alternative method, you can gently brush the power supply wire against a metal part to see if it sparks. This method can help you determine if there’s power, but be cautious to avoid damaging the wiring or fuses.

3. Testing Older Ignition Coils with Ballast Resistors

Older ignition systems with ballast resistors can be more complex. During cranking, the system delivers full 12V to the coil, but reduces the voltage to a lower level once the engine is running due to the ballast resistor. If the ballast resistor fails, the car may start when cranking but will not run properly.

4. Detailed Testing with an Ohmmeter

For a more precise test, you can use an ohmmeter to measure the resistance of the ignition coil:

For standalone coils: Connect one lead of the ohmmeter to the ground and the other to the coil wire that goes to the distributor. A good coil will show very low resistance. If the meter reads above 5-15 ohms or displays O.L., it may be time to replace the coil. For modern coil packs: Connect one lead to where the 12V signal connects and the other to the ground shield on the valve cover. Again, a reading above 5-15 ohms suggests potential issues.

5. Identifying the 12V Lead on a Coil Over System

For car models with coil over systems, follow these steps:

Disconnected the wiring harness from the coil. Test each lead of the connector with a voltmeter while the ignition is in the on position. The lead that shows 12V is the 12V lead. Identify where this lead mates with the coil and test the resistance between these points.

If you don’t get a 12V signal, it indicates that there’s no power reaching the coil, which could be due to a problem with the power supply, wiring, or the ignition coil itself.

Conclusion

Regularly testing your car's ignition coil can save you from expensive repairs and enhance your vehicle’s performance. By using a voltmeter or an ohmmeter, you can easily determine if the coil is receiving the necessary power. Remember to consult a professional if you’re unsure about any steps in the process to avoid damaging your vehicle further.