Rick's Free Auto Repair Advice

Test an ignition coil

How to test an ignition coil

Start with a visual examination of the ignition coil

Test an ignition coil with visual and electrical tests. You’re looking for cracked plastic, damaged ignition coil failureelectrical connector, signs of heat damage or distortion

The ignition coil damage shown above is often caused by driving with worn out spark plugs or worn spark plug wires.

When the spark plug gap erodes to the point where the spark can no longer jump the gap, that electrical energy instead finds its way to ground by firing right through the plastic housing directly to ground. If the vehicle has worn spark plug wires, the high voltage will jump to ground right through the spark plug wire insulation or through the coil tower itself. If you see any cracks or fire-through, that coil must be replaced.

cracked ignition coil

Test for power and ground at the ignition coil connector

Using a multimeter set to DC volts, check for power to the ignition coil with the key in the RUN position. Then check for good ground int he connector.

Test ignition coil resistance with a multimeter

Disconnect the coil’s electrical connector. Set your meter to the ohms scale (200 ohms range). Connect one meter lead to the positive terminal on the coil and the other to the ground terminal of the primary winding. Compare the resistance readings to those shown in the shop manual. This reading will tell you if the insulation on the winding has broken down. Perform the same procedure on the secondary windings. The primary winding for a typical coil pack is from 0.4 to 2 Ohms while the secondary winding is at 6,000 to 10,000 Ohms.

Test ignition coil for shorts

Leave the meter in ohms and disconnect the connectors to the coil. Check for short to ground by touching a meter lead to the positive terminal on the primary winding and the other to a ground spot on the coil.

©, 2020 Rick Muscoplat


Posted on by Rick Muscoplat


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