Ignition coils convert the low voltage from your car’s 12-volt battery into a high voltage.
That high voltage fires up your spark plugs.
However, ignition coils wear out, just like any other component.
When that happens, problems crop up like engine misfires, and you’ll have to replace them.
But how to replace an ignition coil? — you ask.
No worries.
Stick with us, and we’ll tell you how.
This Article Contains
- How to Replace an Ignition Coil
- How to Test Ignition Coils with a Multimeter
- 5 FAQs on Ignition Coil Replacement
How to Replace an Ignition Coil
Ignition coils come in many shapes. Older vehicles may have only a single ignition coil with a distributor and spark plug wires connecting to spark plugs. More recent cars use coil packs with spark plug wires or coil-on-plugs (COP), which sit on the spark plug in the cylinder head cover (also called the valve cover).
Regardless of the ignition system, the steps to change the ignition coils are similar.
NOTE: If you’re unfamiliar with car repairs, it’s always best to let a mechanic do it.
That said, here’s what you’ll need to replace your ignition coil:
- New ignition coil
- Dielectric grease
- Basic shop tools (flat blade screwdriver, ratchet, etc)
- Multimeter (optional)
- Memory saver (optional)
And here’s what to do:
1. Disconnect Negative Battery Cable
First, check your owner’s manual to see if your car needs a memory saver when disconnecting the battery. This helps preserve all the electronic settings.
Make sure the engine is cool before you do anything.
Apply the parking brake, open the engine bay, and remove the engine cover (if there is one).
Disconnect the NEGATIVE battery cable only.
2. Detach Ignition Coil Connectors
Some coils are harder to access than others, and you might need to remove other components (like the intake manifold) to reach them. Check your owner’s manual for details.
Detach the coil connectors. Inspect and clean them of any dirt or corrosion:
A. Single Coil:
- Detach the central coil cable at the top of the ignition coil.
- Detach all ignition cables connected to it. Usually, there’s a positive and negative wire — ensure to mark which is which.
B. Coil Pack:
- Find the bad coil pack. Mark each spark plug wire to that coil pack, as you must reconnect them in the same positions later. You can use a marker or stickers, for example.
- Detach all wires to the coil pack and check them. Spark plug wire damage can also mimic ignition issues.
C. Coil-on–Plug:
To unhook the coil connector, squeeze the pigtail, wiggle it, and pull it straight out. Be careful, as this connector might be old and can break easily. Replacing it can be difficult.
Additionally:
- If replacing more than one COP, it’s best to replace individual coils one at a time.
- If replacing more than one simultaneously, mark the position of each electrical connector attached to the wiring harness.
- If your engine is difficult to get to, consider replacing several coils at once.
3. Unbolt and Remove Old Ignition Coil
Now you can remove the old ignition coil:
A. Single Coil or Coil Pack:
- Loosen the coil’s mounting hardware (bolts, clamps, etc).
- Remove the old coil from its mounting space.
B. Coil-on–Plug:
- Unscrew the coil’s hold-down bolt.
- Twist to detach the coil’s insulating boot from the spark plug and pull the old coil from the valve cover. Be careful, as it can be a bit stuck from being in there for so long. Heat from the engine can make the rubber brittle.
NOTE: If the spark plug boot tears, you’ll need needle nose pliers or a pick to pull out the remaining bits. Be careful not to damage the spark plug porcelain.
- Inspect the old coil on the boot for oil or coolant contamination. Also, check the spark plug socket and wiring harness. This could point to other problems that lead to a misfire.
4. OPTIONAL for Coil-on-Plug: Test the Suspect Coil
If the check engine light pops on, an OBD code scan usually shows which cylinder misfired — the cylinder with the ignition coil issue. However, misfires can happen for many reasons, not always caused by ignition coil failure.
To find out if it’s a bad ignition coil, you can use the steps above and the following, but instead of using a new ignition coil, swap the coil with one from a “good” cylinder. Start the engine and see if the misfire happens on the swapped cylinder. This means the coil is the problem.
If the coils are hard to access, you can use a multimeter to test the old coil for problems.
5. Install New Ignition Coil
Installing the new ignition coil is straightforward:
A. Single Coil:
- Position the new ignition coil.
- Reattach the negative and positive ignition cables.
- Reattach the center coil wire.
B. Coil Pack:
- Position the new ignition coil pack and reinstall all mounting hardware.
- Reconnect all wires. Make sure each spark plug wire is in the correct position.
C. Coil-on-Plug:
- Check that the new coil is a direct replacement of the old coil. Look at the electrical connector, number of terminal pins, and COP length. If the replacement part is too short, it won’t reach the spark plug, and your engine will misfire.
- If needed, apply a bit of dielectric grease to the rubber boot on the new coil. Some coils come pre-greased.
- Orient the new ignition coil in the spark plug socket the same way as the old one. Slide the new coil onto the spark plug. Screw in the hold-down bolt.
- Reattach the electrical connector. Make sure it is snug, and the locking tab is engaged. You can apply a dab of dielectric grease to the connector so it attaches smoothly, but ensure it doesn’t go on any metal contacts.
6. Reconnect the Battery
Remove the memory saver (if used) and reconnect the negative battery cable. Reattach the engine cover. Start the engine and take the car for a test drive. It should run smoother than before the replacement.
If the check engine light still comes on or your vehicle shakes after the ignition coil replacement, switch off your engine and retrace your steps. There’s probably a loose connector.
If all is OK, clear the OBD codes, and you’re done!
Next, we’ll see how to use a multimeter to check a bad ignition coil.
How to Test Ignition Coils with a Multimeter
This method will check the ignition coil’s primary and secondary winding resistance.
IMPORTANT: This test doesn’t simulate a load, so a weak, failing ignition coil may still pass but remain problematic.
Here’s what to do:
- Check the owner’s manual for the correct primary and secondary winding resistance. The manual should also tell you which terminals to check the windings.
- Connect the multimeter’s leads to the indicated touch points.
- Check the multimeter reading against what it should be. Zero means the coil is shorted. A very high reading means the coil is open. Any reading outside of the specified range means you should replace the coil.
Still have questions on replacing ignition coils?
5 FAQs on Ignition Coil Replacement
Here are the answers to some questions on ignition coil problems and replacing it:
1. What Are the Signs of a Bad Ignition Coil?
A faulty coil will often show itself with these symptoms:
- Rough idle or sluggish engine performance (often from engine misfire)
- Engine backfiring
- Problems starting vehicle
- Lit check engine light
- Excessive fuel consumption
Read these automotive articles on bad ignition coil symptoms or ignition coil replacement cost.
2. Can I Replace Ignition Coils Myself?
You can DIY this task if you’re comfortable working with the engine. The ignition coil isn’t always easy to access, so you might have to remove other parts to reach it.
Otherwise, get a mechanic to help sort out ignition coil problems. A mobile mechanic might be a better option as you won’t have to bring your car to a repair shop.
3. Do I Need to Disconnect the Battery to Change the Ignition Coil?
Technically, no, but in truth, it’s much SAFER.
Disconnect the ground (negative) wire from the battery whenever you work on the car’s ignition system (or any electrical system.) This essentially ‘isolates’ the battery.
Taking the positive wire off the battery can be more dangerous because of all the grounded spots where you are swinging your metal wrench. Contacting any of those grounds while accidentally touching the battery positive will cause a short circuit, which can damage things (and you) in many different ways.
4. What if I Don’t Replace a Faulty Ignition Coil?
You should replace a failing ignition coil ASAP.
A faulty coil will cause problems like engine misfire, which may eventually damage other components like your O2 sensors or catalytic converter. Catalytic converters are pretty expensive to replace.
5. How Often to Change Ignition Coils?
There is often no set interval to change ignition coils, but you should have them inspected every 60,000-100,000 miles.
Keep Your Ignition Coils at Peak Performance
Ignition coils are vital to engine performance, longevity, and fuel economy. While you likely won’t have to replace them often, act quickly if signs of ignition coil failure crop up.
If you don’t want to get into the nitty gritty, let AutoNation Mobile Service deal with it.
We’re a mobile auto repair and maintenance solution available 7 days a week.
Contact us, and we’ll send an expert mobile mechanic to help you with your ignition coil issue right from your driveway.