How to Replace an Ignition Coil

A yellow car on the road.
What You'll Need
Electronic tester for the ignition module
Owner's service manual for your vehicle's type and model
Various screwdrivers
Needle nose pliers to help disconnect and reconnect wiring
Wrenches to remove nuts
Tray for screws, bolts and nuts
Several clean dry rags
Portable overhead lighting
Insulated shoes and eye protection

If your vehicle has become difficult to start, replacing the ignition coil may be a solution to your problem. Each automaker's ignition coil may be slightly different so be sure to obtain the correct replacement for your car or truck. Follow the steps below to replace your ignition coil easily and quickly.

Step 1 - Check that the Ignition Coil is the Source of the Problem

Connect the electronic tester to the ignition module and follow the directions in the service guide. The ignition module is located near the distributor in the engine housing. Check the service guide for the exact location. A low energy reading will confirm that the ignition coil is no longer transmitting enough energy to the spark plugs to start the car.

Step 2 - Prepare to Remove the Old Ignition Coil

Disconnect the battery cables from the battery and the engine. Next, loosen the screws holding down all the electrical wiring to the ignition module. Place the screws on a tray to keep them together. Remove the outer housing of the ignition module. Pull out the ignition coil, which looks like a large cylinder with a cap and two electrical leads on top.

Step 3 - Examine the Old Ignition Coil

Check the old ignition coil for a cracked housing, bent or broken electrical leads, a loose or cracked cap, and missing or damaged wire connections. Any of these conditions may have caused it to fail.

Step 4 - Check the Ignition Module Carefully

Examine the whole exterior and interior of the ignition module for clues about what might have caused its failure. Look for missing, bent, broken, cracked, or twisted electrical connections and wiring, damage to the housing or to its porcelain insulation. If some of the wiring is damaged, cut new wires in the correct color and strength to replace them. If the ignition module appears to be damaged, replace the entire ignition module, not just the ignition coil.

Step 5 - Insert the New Ignition Coil

If the ignition module appears to be functional, place the new ignition coil into the ignition module exactly as the old one was situated and reassemble the ignition module. Reconnect the wires to the leads and return the entire ignition module to its correct location. Secure the ignition module in place with the screws, bolts, and nuts you removed to take it out. Check that all wires are connected correctly and that none are protruding from the ignition module housing.

Step 6 - Reconnect the Battery to the Ignition Module

Reattach the battery cables to the engine block and the battery to supply electrical power to the ignition module.

Step 7 - Test the New Ignition Coil for Proper Functioning

Attempt to start the engine. The new ignition coil should transmit sufficient power to enable the vehicle to start easily and effectively.