🔧 GLA - Spark Plug Replacement

On your GLA, spark plugs wear over time and can cause rough idle, misfires, poor fuel economy, and hard starts. Replacing them is a straightforward tune-up job, but you must be careful not to damage the ignition coils or cross-thread the new plugs in the aluminum cylinder head.

Difficulty Level: Intermediate | Estimated Time: 1.0-2.0 hours

---

⚠️ Safety & Precautions

• ⚠️ Work on a fully cool engine to avoid burns and thread damage in the aluminum head.
• ⚠️ Keep dirt out of the plug holes; debris can damage the engine if it falls inside.
• ⚠️ Do not pull on wiring; unplug connectors by the lock tab only.
• ⚠️ Battery disconnect is not strictly required, but disconnecting the negative terminal is a good safety step to prevent accidental shorts.
• ⚠️ Do not use anti-seize on spark plug threads unless the plug manufacturer specifically requires it.

---

🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 10mm socket
• 3/8 in drive ratchet
• 3/8 in drive extension set
• E10 external Torx socket
• 16mm spark plug socket
• Torque wrench 5–60 Nm range
• Small flathead screwdriver
• Compressed air blow gun
• Shop light
• Shop towels

---

🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs - Qty: 4
• Dielectric grease - Qty: 1

---

📋 Before You Begin

• Park on level ground, shift to Park, and set the parking brake.
• Let the engine cool completely (warm aluminum threads can strip more easily).
• If you choose to disconnect the battery: use a 10mm socket to remove the negative terminal and keep it from touching the post.
• Take a quick photo of connectors first.

---

🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover

• Grip the engine cover with both hands and pull straight upward to release the rubber grommets.
• Set it aside where it won’t get stepped on.

Step 2: Unplug the ignition coil connectors

• Use a small flathead screwdriver to gently lift/release the connector lock if needed.
• Pull the connector straight off the coil (don’t yank the wires).

Step 3: Remove the ignition coils

• Use an E10 external Torx socket with a 3/8 in drive ratchet to remove the coil hold-down bolt(s), if equipped.
• Twist the coil slightly to break the seal, then pull it straight up and out.
• Lay coils in order to avoid mix-ups.

Step 4: Clean the spark plug wells

• Use compressed air blow gun to blow out each plug well before removing the plug.
• This prevents sand/grit from falling into the cylinder.

Step 5: Remove the old spark plugs

• Install a 16mm spark plug socket on a 3/8 in drive extension and 3/8 in drive ratchet.
• Loosen each plug counterclockwise and remove it slowly.
• Look at the plug tip for clues (oil, heavy soot, or damage). Abnormal plugs can point to other issues.

Step 6: Install the new spark plugs (by hand first)

• Put the new plug into the 16mm spark plug socket (the rubber insert holds it).
• Thread it into the cylinder head by hand using only the extension (no ratchet at first) until it seats. This helps prevent cross-threading.
• Torque each spark plug using a torque wrench 5–60 Nm range: Torque to 23 Nm (17 ft-lbs).
• Do not adjust the gap on iridium plugs.

Step 7: Reinstall ignition coils

• Apply a tiny smear of dielectric grease inside each coil boot (the rubber part that touches the plug). Dielectric grease helps prevent moisture intrusion and makes future removal easier.
• Push each coil straight down until fully seated on the plug.
• Reinstall coil bolt(s) using an E10 external Torx socket and 3/8 in drive ratchet: Torque to 8 Nm (71 in-lbs).

Step 8: Reconnect connectors and reinstall the engine cover

• Reconnect each coil electrical connector until it clicks/locks in place.
• Reinstall the engine cover by lining up the grommets and pressing straight down firmly.
• If you disconnected the battery, reconnect it using a 10mm socket and tighten snugly.

---

✅ After Repair

• Start the engine and let it idle for 30–60 seconds. It should run smooth with no shaking.
• Check that there’s no check-engine light and no misfire feel on a short test drive.
• If you have a scan tool and a light is on, scan for misfire codes (often caused by a loose connector or a coil not fully seated).
• Recheck the engine cover is fully snapped down and nothing was left loose.

---

💰 DIY vs Shop Cost

Shop Cost: $250-$450 (parts + labor)

DIY Cost: $60-$140 (parts only)

You Save: $190-$310 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.0-1.5 hours.

---

🎯 Ready to get started?

HowToo makes it easy: same-day/2-day shipping on every part, plus all the tools and specialty tools you need! Check out the parts and tools sections below to add everything to your cart.