What causes P0300 on a GMC Terrain?

Common causes of P0300 on GMC Terrain: Ignition coil failure on the 1.5L turbo or 2.0L turbo four-cylinder (common on 2018+ Equinox); Carbon buildup on intake valves from direct injection (GDI) system; Worn or fouled spark plugs due to oil consumption on 2.4L Ecotec engines; Cracked flexible exhaust pipe causing oxygen sensor misreadings and fuel trim errors; Failed PCV valve causing excessive crankcase pressure and oil fouling plugs.

P0300

P0300 GMC Terrain

Q: How much does it cost to fix P0300 on a GMC Terrain?

Fixes for P0300 on GMC Terrain include: Replace all ignition coils and spark plugs as a set with AC Delco OE parts, Perform walnut shell blasting of intake valves to remove carbon deposits, Replace spark plugs and inspect for oil consumption; address piston ring issues if present, Replace cracked flex pipe section and recheck O2 sensor readings, Replace PCV valve assembly and clean intake manifold passages.

Random/Multiple Cylinder Misfire Detected · Powertrain Code · High · Repair: Moderate

What is P0300?

The ECM has detected misfires occurring in multiple or random cylinders. Common causes include worn spark plugs, faulty ignition coils, vacuum leaks, low fuel pressure, or a failing catalytic converter.

When the GMC Terrain triggers code P0300 (random/multiple cylinder misfire detected), it typically points to an issue in the powertrain system. This is a high severity code, so address it promptly to avoid further damage or safety concerns. Below you'll find the most common causes, symptoms, and repair options specific to the GMC Terrain.

This repair is rated moderate, meaning some experience and specialty tools required.

Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your GMC Terrain.

Common Causes on GMC Terrain

Ignition coil failure on the 1.5L turbo or 2.0L turbo four-cylinder (common on 2018+ Equinox)
Carbon buildup on intake valves from direct injection (GDI) system
Worn or fouled spark plugs due to oil consumption on 2.4L Ecotec engines
Cracked flexible exhaust pipe causing oxygen sensor misreadings and fuel trim errors
Failed PCV valve causing excessive crankcase pressure and oil fouling plugs

Symptoms

Rough idle with noticeable engine vibration
Engine shaking or stumbling under load
Loss of power during acceleration
Check engine light flashing intermittently
Poor fuel economy
Hesitation or stumble on acceleration

Recommended Fixes

Replace all ignition coils and spark plugs as a set with AC Delco OE parts

Perform walnut shell blasting of intake valves to remove carbon deposits

Replace spark plugs and inspect for oil consumption; address piston ring issues if present

Replace cracked flex pipe section and recheck O2 sensor readings

Replace PCV valve assembly and clean intake manifold passages

Notes for GMC Terrain

The 1.5T Ecotec in 2018-2022 Equinox has known carbon buildup issues from direct injection.

P0300 GMC Terrain

What is P0300?

Common Causes on GMC Terrain

Symptoms

Notes for GMC Terrain

Check GMC Terrain Specs