Spark plugs

Summary

Source: owner's manual / last verified 2026-10-16 (2018 GMC Terrain owner's manual, engine specifications and maintenance parts (opens in a new tab)).

Safety

• Let the engine cool before you work around the plugs.
• Do not put a gap from one engine onto another.
• Do not invent a coil-bolt torque.

Symptoms

• The gap in the table is for replacement spark plugs.
• A diesel row with a dash is not a gas plug.

Diagnosis

1. 1.5L L4 gas (LYX), all-wheel drive: 0.60–0.70 mm (0.024–0.028 in). GM 12673527, ACDelco 41-153.
2. 1.5L L4 gas (LYX), front-wheel drive: 0.60–0.70 mm (0.024–0.028 in). GM 12673527, ACDelco 41-153.
3. 2.0L L4 gas (LTG), all-wheel drive: 0.75–0.90 mm (0.030–0.035 in). GM 12647827, ACDelco 41-125.
4. 2.0L L4 gas (LTG), front-wheel drive: 0.75–0.90 mm (0.030–0.035 in). GM 12647827, ACDelco 41-125.
5. 1.6L L4 diesel (LH7): the spark-plug gap cell is a dash, and the parts table does not list a plug.
6. No plug torque, coil torque, or firing order was in the pages read. This page does not add them.

Tools

• Spark-plug socket

  The book requires the correct replacement plug. It does not print the socket size.

Specifications

Steps

1. 01Read the VIN code

   The eighth character of the VIN is the engine code in this book. 1.5L L4 gas (LYX), all-wheel drive: 0.60–0.70 mm (0.024–0.028 in). GM 12673527, ACDelco 41-153. 1.5L L4 gas (LYX), front-wheel drive: 0.60–0.70 mm (0.024–0.028 in). GM 12673527, ACDelco 41-153. 2.0L L4 gas (LTG), all-wheel drive: 0.75–0.90 mm (0.030–0.035 in). GM 12647827, ACDelco 41-125. 2.0L L4 gas (LTG), front-wheel drive: 0.75–0.90 mm (0.030–0.035 in). GM 12647827, ACDelco 41-125. 1.6L L4 diesel (LH7): the spark-plug gap cell is a dash, and the parts table does not list a plug.

2. 02Gap only to the printed range

   The table says the gap is for replacement spark plugs.

3. 03Stop where the book stops

   No removal torque is printed. A firing order is not in the engine-spec table that was read.

Common mistakes

• Gapping a diesel that has a dash in the gap cell.
• Using the 1.5L gap on the 2.0L, on a Terrain that has both.
• Inventing a coil torque.

Parts and tools

Outbound links only. BaySheet does not sell parts. Confirm fitment on the retailer page. Amazon links are searches for a real part name plus this vehicle. Tool rows do not get a product search. The search is not a part number.

• Part

  GM 12673527

  Spark plug for the 1.5L L4 gas (LYX), all-wheel drive. ACDelco 41-153. Gap 0.60–0.70 mm (0.024–0.028 in).

  2018 Terrain spark plug parts (opens in a new tab)Search Amazon.com (affiliate link) (opens in a new tab)As an Amazon Associate I earn from qualifying purchases.

• Part

  GM 12673527

  Spark plug for the 1.5L L4 gas (LYX), front-wheel drive. ACDelco 41-153. Gap 0.60–0.70 mm (0.024–0.028 in).

  2018 Terrain spark plug parts (opens in a new tab)Search Amazon.com (affiliate link) (opens in a new tab)As an Amazon Associate I earn from qualifying purchases.

• Part

  GM 12647827

  Spark plug for the 2.0L L4 gas (LTG), all-wheel drive. ACDelco 41-125. Gap 0.75–0.90 mm (0.030–0.035 in).

  2018 Terrain spark plug parts (opens in a new tab)Search Amazon.com (affiliate link) (opens in a new tab)As an Amazon Associate I earn from qualifying purchases.

• Part

  GM 12647827

  Spark plug for the 2.0L L4 gas (LTG), front-wheel drive. ACDelco 41-125. Gap 0.75–0.90 mm (0.030–0.035 in).

  2018 Terrain spark plug parts (opens in a new tab)Search Amazon.com (affiliate link) (opens in a new tab)As an Amazon Associate I earn from qualifying purchases.

• Tool

  Spark-plug socket

  The book requires the correct replacement plug. It does not print the socket size.

  McMaster-Carr spark plug sockets (opens in a new tab)

Questions

Sources

• 2018 GMC Terrain owner's manual, engine specifications and maintenance parts (opens in a new tab). General Motors. Published 2017-09-15. Read 2026-10-16.

Checklist and email notes

The maintenance checklist is on the site now. The email list is not sending yet, so this box will not store an address.

Other repairs on this 2018 Terrain

All GMC Terrain repairs

This repair on other vehicles

These guides cover the same kind of work. Their numbers belong to those vehicles, not to this one.