How to Replace Ignition Coils on a 2018 Cadillac XT5 (Fix Misfires & P0300–P0306)
Step-by-step DIY instructions with tools, parts list, safety tips, and 89 in-lb (10 Nm) torque spec for 2017, 2018, 2019, 2020, 2021, 2022, 2023
How to Replace Ignition Coils on a 2018 Cadillac XT5 (Fix Misfires & P0300–P0306)
Step-by-step DIY instructions with tools, parts list, safety tips, and 89 in-lb (10 Nm) torque spec for 2017, 2018, 2019, 2020, 2021, 2022, 2023
🔧 XT5 - Ignition Coil Replacement
Ignition coils sit on top of the spark plugs and create the high voltage needed to fire the engine. Replacing a weak or failed coil can fix misfires, rough running, and flashing check-engine light (often with codes like P0300–P0306).
Difficulty Level: Intermediate | Estimated Time: 1.0-2.0 hours
⚠️ Safety & Precautions
- ⚠️ Work on a cool engine; coils sit near hot components.
- ⚠️ Keep the key/fob away from the vehicle so the engine can’t accidentally crank.
- ⚠️ Do not pull on wiring; press the connector lock and pull on the plug body.
- ⚠️ If you disconnect the battery, you may lose radio presets.
🔧 Required Tools
You'll need the following tools for this repair:
- Safety glasses
- Nitrile gloves
- 10mm socket
- 1/4" drive ratchet
- 6" extension (1/4" drive)
- Trim clip removal tool
- Small flathead screwdriver
- Torque wrench (inch-pound)
- Flashlight
🔩 Required Parts
HowToo sells all the parts you need for this repair:
- Ignition coil - Qty: 1 (or Qty: 6 if replacing all)
- Dielectric grease - Qty: 1
- Intake duct clamp (if damaged) - Qty: 1
📋 Before You Begin
- 🅿️ Park on level ground and set the parking brake.
- Open the hood and let the engine cool fully.
- If you choose to disconnect the battery: use a 10mm socket to remove the negative terminal and isolate it so it can’t spring back.
- Tip: Replacing coils in pairs or all six is often smarter.
🔨 Step-by-Step Instructions
Follow these steps in order:
Step 1: Remove the engine cover
- Grip the cover with both hands and pull straight upward to release the rubber grommets.
- Use a flashlight to confirm nothing is still clipped or snagged.
Step 2: Make room (if needed) to reach the coil(s)
- If access is tight, loosen the intake duct clamp(s) with a flathead screwdriver.
- Use a trim clip removal tool to pop any plastic retainers holding the duct/hoses in place.
- Move the duct aside gently (don’t crack it).
Step 3: Unplug the coil electrical connector
- Press the connector locking tab (use a small flathead screwdriver only if the tab is stubborn) and pull the connector straight off.
- Tip: Wiggle the connector—don’t yank the wires.
Step 4: Remove the coil mounting bolt
- Use a 10mm socket, 1/4" drive ratchet, and 6" extension to remove the bolt holding the coil down.
- Set the bolt aside where it won’t fall into the engine bay.
Step 5: Remove the ignition coil
- Twist the coil slightly left/right to break the seal, then pull straight upward to remove it.
- If it feels stuck, keep twisting—do not pry hard against the valve cover.
Step 6: Prep and install the new coil
- Apply a small pea-sized amount of dielectric grease inside the new coil boot (dielectric grease is a non-conductive grease that helps prevent moisture and makes future removal easier).
- Push the coil straight down onto the spark plug until you feel it fully seat.
Step 7: Reinstall the coil bolt and torque it
- Start the bolt by hand first to avoid cross-threading.
- Use a 10mm socket to snug it down.
- Use a torque wrench (inch-pound) and 10mm socket: Torque to 89 in-lb (10 Nm).
Step 8: Reconnect the coil connector
- Push the connector on until you feel/hear a click.
- Use a flashlight to verify the connector is fully seated and the lock is engaged.
Step 9: Reassemble what you moved
- Reposition the intake duct and reinstall any retainers using the trim clip removal tool.
- Tighten intake duct clamp(s) with a flathead screwdriver (snug, not crushing-tight).
- Reinstall the engine cover by lining up the grommets and pushing straight down.
✅ After Repair
- Start the engine and let it idle for 1–2 minutes. It should run smooth.
- If the check-engine light was flashing before, confirm it’s gone and the engine isn’t misfiring.
- If you disconnected the battery, reset your clock/radio presets.
- If the check-engine light stays on, the code may need to be cleared after the repair.
💰 DIY vs Shop Cost
Shop Cost: $250-$650 (parts + labor, depends on number of coils)
DIY Cost: $45-$420 (parts only, depends on 1 vs 6 coils)
You Save: $200-$300+ 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.


















