Owners of other General Motors vehicles such as the Buick Verano, Regal, LaCrosse, Cascada, Encore, Enclave, Envision, GMC Canyon, Sierra 1500, Acadia, Yukon, Denali, Savana, Spark, Sonic, Cruze, Malibu, Impala, Volt, Camaro, Corvette, SS, Trax, Equinox, Traverse, Tahoe, Suburban, Colorado, Silverado and Express may also find these DIY instructions to be helpful.

The OEM iridium tipped spark plugs in this 2016 Terrain SLT are the ACDelco 41-109.

A few other compatible replacement spark plugs with their part numbers are as follows: Autolite XP5263, Denso ITV20, NGK (6509) LTR6IX-11 and ACDelco 41-834.

The tools and other items needed to complete this procedure include a Torx T30 screwdriver, a flat head screwdriver, a 10mm socket, a 1/4" drive ratchet, a 5/8" spark plug socket, an extension bar, a 3/8" drive ratchet and a tube of dielectric grease.

The OEM part number for the intake manifold gasket is GM 12647263 (also known as ACDelco 12647263).

Note - In this guide I'm only checking the front three plugs since this vehicle only has 30,000 miles on the odometer. To access all three rear plugs, the intake manifold must be removed. I provide written instructions from the service manual down below.

Set the T30 screw aside in a safe place.

Twist off the oil filler cap in the counterclockwise direction and put it aside with the screw.

If you have access to compressed air or a wet/dry shop vacuum, thoroughly clean off the top of the engine to help reduce the chance of having debris drop down in to the spark plug wells.

You will have to pull the rubber hose that runs across the top of the front ignition coils out of its socket on the right (driver) side.

To replace the 3 spark plugs on the rear of the engine, the intake manifold will need to be removed.

It would also be best to have an assortment of wobble extension bars in different sizes and also a universal swivel joint.

Here are the written instructions from the shop manual for removing and replacing the intake manifold on the GM 3.6L V6 engine:

Intake Manifold Replacement
Removal Procedure
 1. Remove the intake manifold cover. Refer to the Intake Manifold Cover Replacement.
 2. Remove the air cleaner outlet duct. Refer to the Air Cleaner Outlet Duct Replacement.
 3. Remove the power steering fluid reservoir (upper bracket only).
 4. Remove the power brake booster vacuum check valve and hose. Refer to the Power Brake Booster Vacuum Check Valve and Hose Replacement.
 5. Remove the coolant air bleed pipe. Refer to the Engine Coolant Air Bleed Pipe Replacement.
 6. Disconnect & remove the positive crankcase ventilation (PCV) tube (1) from the intake manifold & right camshaft cover.
 7. Remove the evaporative emission (EVAP) hose from the intake manifold & EVAP solenoid.
 8. Remove the fuel pipe shield. Refer to the Fuel Pipe Shield Replacement.
 9. Disconnect & reposition the wire harnesses as necessary.
10. Remove the intake manifold bolts (1).
11. Remove the intake manifold assembly (2).
12. Remove and discard the intake manifold gasket (1).
13. To clean the intake manifold, refer to the Intake Manifold Cleaning and Inspection.
14. To disassemble the intake manifold, refer to the Intake Manifold Disassemble.
Installation Procedure
 1. Assemble the intake manifold if needed. Refer to Intake Manifold Assemble.
 2. Install the NEW intake manifold gasket (1).
 3. Install the intake manifold assembly (2).
Caution: Refer to the Fastener Caution.
 4. Install the intake manifold bolts (1).

This should apply to any GM vehicle equipped with the LFX or LLT 3.6L V6 engines such as the Cadillac CTS, STS, ATS, SRX, XTS, Buick Enclave, Chevy Traverse, GMC Acadia, LaCrosse, Camaro, Caprice, Colorado, Canyon, Equinox, Impala and the Holden Commodore.

Once the power plug has been unlocked, push down the black plastic tab to release the connector before sliding it straight off the ignition coil housing.

Set the 10mm bolt aside in a safe place.

Lift the ignition coil housing out of the spark plug well and set it aside in a safe place.

I always attach the spark plug socket to the extension bar with some tape to prevent it from falling off in to the spark plug well.

Lower the socket over the top of the old spark plug.

Loosen the old spark plug by turning it counterclockwise.

Try to avoid using excessive force to loosen the old spark plug, which may cause it to crack or break off.

If the spark plug won't turn, spray in some penetrating oil such as PB Blaster, Liquid Wrench or Kano Kroil and wait 15-30 minutes or more before trying again. If you don't have any penetrating oil, try spraying some WD-40 or just warm up the engine for a few minutes to expand the metal engine block.

Once the spark plug is loose, detach the ratcheting wrench from the extension bar and spin it out the rest of the way by hand.

Inspect the old spark plug.

If the electrode end of the old spark plug looks ashy white, the plugs might have been exposed to high temperatures such as engine overheating or they could be the incorrect heat range for your driving conditions and/or environment.

If the old spark plugs are dark grey or covered in black soot, the engine could be burning oil and should be checked by a professional mechanic.

The OEM (original equipment manufacturer) spark plugs on this 2016 Terrain are the ACDelco 41-109 iridium.

I recommend buying either the OEM plugs or the Autolite XP5263 spark plugs which have excellent reviews on Amazon.

If you have a spark plug gap gauge, check the gap on the new spark plugs. They should already be pre-gapped to the correct setting from the factory.

An optional step is to apply some anti-seize grease to the threads on the new spark. Most spark plug manufacturers recommend that you not use anti-seize since it can lead to over tightening. But it your old spark plugs were very difficult to remove, you may want to consider using some. Just remember to use less torque when you tighten the plugs.

Push the new spark plug in to the socket.

Your spark plug socket should have a rubber insert or a strong magnet to hold the new spark plug in place.

Lower the new spark plug in to the cylinder well.

Attach the 3/8" drive ratchet to the extension bar and tighten the new spark plug to just past barely past the point when you feel the crush washer collapse.

If you are re-installing the old spark plugs, only tighten them to just a small fraction of a turn past hand tight.

(Remember, if you used anti-seize lubricant, you'll have to be extra careful to avoid over tightening the new plug.)

Try to avoid using excessive force to prevent from cracking the new plug or stripping the aluminum threads.

Double check that the new spark plug is tight before moving on to the next step.

The dielectric grease will help prevent corrosion and also keep out any moisture, dust or debris.

Rotate the ignition coil back and forth a few times to spread the dielectric grease.

Re-insert the 10mm bolt and spin it in a few turns in the clockwise direction by hand to prevent it from becoming cross threaded.

Tighten the bolt by turning it clockwise with the 10mm socket and the 1/4" drive ratchet to just past hand tight.

Try to avoid over tightening the 10mm bolt to prevent from cracking the plastic ignition coil housing.

Slide the grey plastic tab in to secure the power plug.

Push the end of the rubber hose back in to place on the right (driver) side of the engine.

Replace the oil filler cap by twisting it on in the clockwise direction.

Start the engine and listen closely for any strange noises that might indicate a loose spark plug, disconnected vacuum line or a loose electrical connector.

Be sure to record the spark plug change in your vehicle's service records.

For more, check out my other 2010-2016 GMC Terrain DIY Repair & Maintenance Guides.