This procedure covers removal and replacement of spark plugs on the 2014-2019 Toyota Corolla 1.8L inline-4 engine.

Warnings

Tools required

Parts

• Spark plugs (iridium) × 4 — 90919-01253 or equivalent

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to cool completely (minimum 2 hours after operation)
3. Disconnect negative battery terminal to prevent accidental ignition system activation
4. Gather all tools and new spark plugs before beginning

Procedure

1. 1

   Remove engine cover
   Grasp the plastic engine cover at the front corners and pull upward firmly to release the retention clips. The cover is held by four clips and does not require tools for removal. Set cover aside in a clean area.
2. 2

   Remove ignition coils
   Disconnect the electrical connector from each ignition coil by pressing the tab and pulling straight up. Remove the single 10mm bolt securing each coil. Grasp each coil firmly and pull straight up with a slight twisting motion to remove. Mark or remember the cylinder position of each coil for reinstallation.
   ⚠Do not pull on wiring harness. Pull only on the connector body to avoid damaging wires.
   Torque spec

   Ignition Coil Bolt10 Nm (8 lb-ft)
3. 3

   Clean spark plug wells
   Use compressed air or a clean lint-free rag to remove any debris, dirt, or oil from around the spark plug wells. This prevents contamination from falling into the cylinder when the plug is removed.
   ℹ️If oil is present in spark plug wells, the valve cover gasket may be leaking and should be inspected.
4. 4

   Remove old spark plugs
   Using the spark plug socket with extension, carefully loosen each spark plug by turning counterclockwise. Once loose, remove by hand to prevent cross-threading. Inspect each plug for abnormal wear, fouling, or electrode damage which may indicate engine problems.
   ⚠Use caution when breaking plugs loose. Excessive force on a seized plug can break the ceramic insulator or damage threads.
5. 5

   Inspect old spark plugs
   Examine the electrode and insulator of each removed plug. Normal wear shows light brown or gray deposits. Black sooty deposits indicate rich fuel mixture, white blistered deposits indicate overheating, and oil fouling indicates internal engine oil consumption.
6. 6

   Prepare new spark plugs
   Verify gap on new spark plugs using gap tool. Factory gap should be 0.043 inches (1.1mm). Adjust if necessary by carefully bending the ground electrode. Apply a small amount of anti-seize compound to the threads of each spark plug, avoiding the electrode area.
   ⚠Do not allow anti-seize to contact the electrode or insulator as this can cause misfires.
7. 7

   Install new spark plugs
   Thread each new spark plug into the cylinder head by hand, turning clockwise until finger-tight. This ensures proper thread engagement and prevents cross-threading. Once hand-tight, use the torque wrench and spark plug socket to tighten to specification.
   ⚠️Always torque spark plugs to exact specification. Under-torquing can cause plugs to blow out under compression; over-torquing will strip aluminum threads.
   Torque spec

   Spark Plug19 Nm (14 lb-ft)
8. 8

   Reinstall ignition coils
   Apply a thin coat of dielectric grease to the inside of each coil boot if desired. Press each ignition coil firmly into place over its corresponding spark plug, ensuring it seats fully. Install and torque the 10mm retention bolt for each coil. Reconnect electrical connectors to each coil until they click into place.
   Torque spec

   Ignition Coil Bolt10 Nm (8 lb-ft)
9. 9

   Reinstall engine cover
   Align the engine cover clips with their mounting points on the valve cover and intake manifold. Press down firmly on all four corners until each clip engages with an audible click.
10. 10

    Reconnect battery and test
    Reconnect the negative battery terminal. Start the engine and verify it runs smoothly without misfires or rough idle. Check for any error codes using an OBD-II scanner if the check engine light illuminates.

Reassembly

1. Ensure all ignition coil electrical connectors are fully seated and locked
2. Verify engine cover is securely clipped at all four attachment points
3. Clear any diagnostic trouble codes that may have set during the procedure

Verification

• Start engine and listen for smooth, even idle with no misfires or hesitation
• Rev engine gently to 2000-3000 RPM and confirm smooth operation
• Verify no check engine light or misfire codes are present
• Inspect ignition coil area for proper seating and secure connections
• Test drive vehicle under light acceleration to confirm proper performance

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