How to Test an Ignition Coil?
3 Answers
Testing methods for an ignition coil are as follows: 1. Turn the vehicle's ignition switch to the ON position and unplug the ignition coil connector; 2. Use a multimeter to measure pin 3 with one probe and ground with the other; 3. Unplug the ignition coil connector, measure pin 1 with one probe and pin 5 of the ECU with the other; 4. Unplug the ignition coil connector, measure pin 2 with one probe and pin 2 of the ECU with the other; 5. Use a multimeter to check if the resistance of the sensor's primary coil is approximately 0.9 ohms. Precautions for using an ignition coil include: 1. Avoid exposing the ignition coil to heat or moisture; 2. Do not turn on the ignition switch when the engine is not running.
Last time I tinkered with the ignition coil myself, it was quite simple. Open the hood and first check for any cracks or oil stains on the exterior, as that could indicate internal leakage. Then use a multimeter to measure the resistance: unplug the coil connector, measure the primary coil resistance, which should normally be around 0.5 to 2 ohms; then measure the secondary coil, approximately 6 to 15 kilo-ohms. Make sure the engine is cold for accurate readings. If the resistance is off, the coil is definitely faulty. If you don’t want to disassemble it, you can also test the spark by cranking the engine: remove the spark plug and connect it to the coil, then check if the ignition spark is strong and stable. That time, I found one cylinder misfiring, and the coil resistance was fluctuating—so I promptly replaced it, and the engine ran smoothly again. Remember to turn off the power to prevent electric shock, and keep gloves handy. Regularly clean engine oil stains to prevent corrosion and part damage, which can extend the lifespan.
With over a decade of auto repair experience, I'm well-versed in ignition coil testing. It's generally a three-step process: First, visually inspect for surface damage. Then, use a multimeter to measure resistance values—the primary terminal to ground should display a specific range. For more professional diagnostics, use an oscilloscope to monitor the ignition waveform; abnormal waveforms indicate potential faults. In practice, common issues include resistance exceeding limits or secondary leakage causing misfires, especially in older cars where aging high-voltage wires affect the coil. When replacing spark plugs, check for loose coil connectors and clean corroded contacts. Diagnostic tools can also read fault codes to assist in judgment. Don’t forget to test with the engine running—if the coil feels excessively hot to the touch, it’s likely beyond repair. Timely replacement prevents bigger problems down the line.
