How do you remove spark plugs from a Subaru?
You remove spark plugs from a Subaru by safely accessing each plug through its ignition coil or boot, loosening the plug with a spark plug socket, and reinstalling with the correct gap and torque. The exact steps vary by engine type, but the general method is consistent across most modern Subarus.
Know your engine layout
Subarus use a mix of flat-four (boxer) and flat-six layouts. Modern four-cylinders typically use coil-on-plug ignition, where each cylinder has its own coil pack. Some older or specialty models may still use coil-on-wires or different access paths. Identifying whether your engine uses COS or separate ignition components helps determine the exact removal method and access points. Always ensure the engine is cold before starting work.
Tools and safety
Gather the right tools and follow safety steps to minimize the risk of damage or injury.
- Spark plug socket with a rubber insert (long-reach) and a ratchet
- Our recommended extensions (6–12 inches) for reaching recessed plugs
- Torque wrench appropriate for small fasteners
- Gloves and eye protection
- Small screwdriver or pick for releasing connectors
- Penetrating oil (optional for stubborn plugs)
- New spark plugs of the correct type and gap for your model
Always disconnect the negative battery cable and let the engine cool before starting. Removing engine covers or ducts may be necessary to access the plugs.
Removing spark plugs on coil-on-plug (COS) engines
Access and preparation
This method is standard for most modern Subarus with COS ignition. Each cylinder has its own coil pack, which you remove to expose the spark plug.
Before you begin, ensure the engine is cool and the battery is disconnected. This reduces the risk of electric shock and protects sensitive electronics.
Access may require removing an engine cover, intake ducting, or undertray to reach the coil packs.
- Disconnect the electrical connector from each coil pack by pressing the release tab and pulling straight up.
- Remove the coil pack mounting bolt(s) with the appropriate size (usually 6–10 mm) and lift the coil straight up to expose the plug
- Inspect the coil boot for wear or damage as you go; set it aside with the corresponding coil
With the plug exposed, you’re ready to remove it using the spark plug socket. If the plug is stubborn, a small amount of penetrating oil and a brief wait can help.
Removing and inspecting the spark plug
Use a spark plug socket with a long extension to break the plug loose, then extract it carefully to avoid cross-threading.
- Place the socket over the plug and turn counterclockwise to loosen; keep the plug straight to protect the threads
- Remove the plug and inspect its condition (foulings, oil, or electrode wear) for signs of engine issues
Repeat for each cylinder. If a plug is stubborn, avoid forcing; apply penetrating oil and retry after a short wait.
Removing spark plugs on traditional ignition coil-with-wires (older Subarus)
Access considerations for older layouts
Some older Subarus use individual ignition coils with spark plug wires. Access involves removing the boot from the plug and possibly detaching the coil or related harnesses to reach the plug.
Do not pull on the spark plug wire itself. Grasp the boot firmly and pull straight away from the plug to prevent wire damage.
- Disconnect the boot from the spark plug by pulling the boot straight off (not the wire)
- If needed, remove any retaining clips or wire harnesses obstructing access
- Use a spark plug socket to loosen and remove the plug
Inspect boots and coils for wear; plan to replace worn components along with the plugs if needed.
Installing new plugs and reassembly
Plugs, gaps, and torque
Install the correct plugs and set the gap as specified by Subaru or the plug manufacturer. For many modern Subaru engines, gaps are commonly in the range of 0.028–0.032 inches, but always verify for your model.
- Thread each plug by hand to avoid cross-threading, then tighten to the factory torque specification for your engine (typical range is about 13–16 ft-lbs / 18–22 Nm for many four-cylinder Subarus; check your manual for the exact value)
- Reconnect and secure each coil pack or boot, ensuring all electrical connectors click into place
- Reinstall any engine covers, ducts, or components removed to gain access
- Reconnect the negative battery cable and start the engine to confirm smooth operation
If the engine runs rough or misfires, recheck that each plug is seated properly and that each coil/boot is securely connected.
Common issues and maintenance tips
Spark plug removal can reveal underlying engine issues. Look for oil in the plug wells, heavy carbon buildup, or worn electrodes, which may indicate valve seals, piston rings, or fueling problems. Replacing plugs at the intervals recommended by Subaru helps maintain performance and fuel efficiency.
Summary
Removing spark plugs from a Subaru is straightforward when you know your engine layout and follow proper safety and torque guidelines. Modern vehicles with coil-on-plug ignition require removing each coil pack to access the plug, while older layouts may use boots or wires to reach the plug. Use the correct plug type, set the proper gap, and torque to spec. When in doubt, consult your vehicle’s service manual or a qualified technician.
Final note: If you’re unsure about any step, seek professional assistance. Ignition components carry electrical risk, and incorrect torque or cross-threading can lead to costly damage.
