P0300 on a 2015 GMC Terrain

P0300 is a generic OBD2 powertrain code for random or multiple cylinder misfire. Unlike P0301 through P0308, it does not point to one specific cylinder, so the cause can be ignition, fuel, air, sensor, or mechanical.

Not your vehicle? See general P0300 info.

Most common causes on the 2015 GMC Terrain

Ranked from 315 NHTSA owner complaints filed for this vehicle.

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1
Excessive oil consumption from worn piston rings fouling spark plugs
High severity
Widely reported on this engine: oil burning past the rings fouls plugs and lowers compression, and several owners describe rough running/stalling and a specific dead cylinder tied directly to oil starvation.
Reported in 6 NHTSA complaints
2
Worn or stretched timing chain (2.4L Ecotec)
High severity
Multiple owners report timing chain stretch/failure causing jerking, rough running, a P0016 crank/cam correlation fault, and outright chain breakage -- all of which throw cam timing off and produce a multi-cylinder misfire.
Reported in 5 NHTSA complaints
Parts:timing chain timing chain tensioner timing chain guides
3
Carbon-fouled intake valves / oil sludge buildup
Medium severity
Owners describe sludge and carbon blocking the intake manifold and head, which disrupts airflow and combustion on affected cylinders.
Reported in 2 NHTSA complaints
4
Worn spark plugs
Low severity
Plugs past their service interval or fouled by oil lose spark energy and misfire under load; pull and inspect plugs for wear/fouling pattern.
Common cause
Parts:spark plugs
5
Failing ignition coil(s)
Medium severity
A weak or cracked coil drops spark to one cylinder, typically showing as a single repeating misfire; swap coils cylinder-to-cylinder to confirm.
Common cause
Parts:ignition coil
6
Clogged or leaking fuel injector
Medium severity
An injector delivering too little (or dribbling) fuel starves or floods a cylinder, producing a misfire isolated to that cylinder.
Common cause
Parts:fuel injector
7
Vacuum leak (intake gasket, hoses)
Medium severity
Unmetered air leaning out one or more cylinders can present as a misfire, especially at idle; smoke-test the intake tract.
Common cause
8
EGR valve fault
Low severity
A stuck-open EGR valve dilutes the intake charge excessively and can cause a rough idle/misfire; test EGR flow and check for carbon sticking.
Common cause
Parts:EGR valve

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These causes are aggregated from NHTSA owner complaints and general repair knowledge — this is not a diagnosis. P0300 on your car still needs shop confirmation before any repair.

Common symptoms

Flashing or steady check engine light
Rough idle
Shaking under acceleration
Loss of power
Fuel smell from exhaust

What to check before replacing parts

Scan for cylinder-specific misfire codes

Look for: A companion P0301–P0308 pins the misfire to one cylinder — start there. P0300 with no cylinder code points at something hitting several at once: fuel pressure, a large vacuum leak, or timing.

Inspect the spark plugs and coils

Look for: Pull the plugs: black/sooty = rich, oily = oil intrusion, white/blistered = lean or overheating, cracked porcelain or an out-of-spec gap = replace. Then swap a coil to another cylinder — if a cylinder-specific code follows the coil, the coil is bad.

Check fuel trims for a vacuum leak

Look for: High positive short- and long-term trims (worst at idle, improving as RPM rises) mean unmetered air is getting in. Smoke-test the intake and listen for hissing.

Verify fuel pressure

Look for: Compare running/cranking pressure to the vehicle spec. Low or dropping pressure starves multiple cylinders and reads as a random misfire — suspect the pump, filter, or regulator.

Compression / leak-down test if ignition and fuel check out

Look for: A cylinder 15%+ below the others, or leak-down hissing from the intake (intake valve), exhaust (exhaust valve), or oil filler (rings), means the misfire is mechanical — not a swap-in part.

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Matching symptoms

Car Runs Rough Flashing Check Engine Light