How to test a faulty coil pack

Written by mark robinson
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How to test a faulty coil pack
An ohmmeter is needed for testing the coil packs. (The Readout image by Cinneman from Fotolia.com)

In the past, most vehicles relied on an ignition system that featured a distributor mounted in front of or behind the engine. Today's modern vehicles come with distributorless ignition systems, or DIS, that replace the distributor with a more efficient and longer lasting coil pack. Testing these coil packs can help pinpoint a no-start or misfire condition and make sure the packs are in proper working order.

Skill level:
Moderate

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Things you need

  • Ratchet and socket set
  • Ohmmeter

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Instructions

  1. 1

    Open the bonnet of your vehicle. Disconnect the negative battery cable. Locate your vehicle's coil pack by tracing the spark plug wires from the spark plug itself back to the coil pack.

  2. 2

    Disconnect the spark plug wires from the coil pack, one at a time. Label each wire to keep track of the correct order. Disconnect the electrical connectors from the coil pack and use a ratchet and socket to remove the coil pack from the engine bay.

  3. 3

    Use an ohmmeter to measure the primary resistance on the coil pack. Set the ohmmeter to 10 ohms. Place one lead on the centre prong of the coil pack's electrical connector and the other lead on each of the spark plug terminals. The ohmmeter should read below 2 ohms. If the readings are above 2 ohms, have the coil pack replaced.

  4. 4

    Measure the secondary resistance on the coil pack. Set the ohmmeter to 20,000 ohms. Place both leads on each spark plug terminal. The ohmmeter should read between 6,000 to 30,000 ohms. If the readings are above 30,000 ohms or below 6,000 ohms, replace the coil pack.

  5. 5

    Reinstall the coil pack into the engine bay and reconnect all the electrical connectors. Plug the spark plug wires into the coil pack in the correct order. Reconnect the negative battery cable and close the bonnet.

Tips and warnings

  • Always exercise caution when working on a vehicle's electrical system. Disconnect the battery whenever possible to reduce the likelihood of shock and serious injury.

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