P0300 Code on a GMC: Random/Multiple Cylinder Misfire Detected (GMC Guide)

P0300 on a GMC is GM's "Engine Misfire Detected" code. The engine control module (ECM) saw misfires it could not pin on one cylinder, or saw them on several cylinders at once. On a GMC that one code covers a lot of hardware: a Sierra or Yukon small-block V8 that shuts cylinders off to save fuel, a 4.3L V6 in a Sierra or Savana, a 3.6L V6 in an Acadia or Canyon, a turbo four in a Terrain, or an inline five in an older Canyon. GM's bulletins for each of those point somewhere different. The surprise: on many GMC misfire bulletins, GM's first step is not "replace the coils." It is watching the valves move on a Sierra with a suspected collapsed lifter, swapping the cylinder deactivation solenoids side to side on an Acadia V6, or checking the charge air cooler for rainwater on a Terrain 1.5T. This page is the hub for our GMC misfire guides. Start here, then use the cylinder pages (P0301–P0305) once you know which cylinders are counting.

What Does P0300 Mean on a GMC?

The ECM watches crankshaft speed through the crankshaft position sensor. Every cylinder that fires gives the crank a small push. When a cylinder fails to fire, the crank slows for an instant and the ECM counts a misfire. When the counts are spread across cylinders, or the ECM can't assign them cleanly, it sets P0300. When one cylinder is clearly at fault it also sets that cylinder's code, P0301 through P0308. That's why GM bulletins usually list P0300 together with the single-cylinder codes.

A misfire comes down to four things: no spark, the wrong amount of fuel, no compression (valves, lifters, rings, pistons), or something in the cylinder that shouldn't be there, such as coolant or water. P0300 tells you one of those happened. The per-cylinder misfire counts on your scan tool are what narrow it down. For the GM-wide background, see our P0300 GM diagnosis guide.

Which GMC Engines Can Set P0300

Every gasoline GMC with OBD-II can set P0300. Which cylinder codes can follow it depends on the cylinder count. Cylinder deactivation matters too, because GM's truck bulletins keep pointing at the cylinders that switch off.

Duramax diesels run a different set of diagnostics and are outside this guide. The Hummer EV and Sierra EV have no engine and can't set P0300.

Read the Pattern Before You Replace Anything

The most useful screen on your scan tool is the misfire count for each cylinder. GM's bulletins sort themselves by pattern, so your diagnosis should too:

• One cylinder far ahead of the rest — go to that cylinder's guide: P0301, P0302, P0303, P0304 or P0305. Each covers where that cylinder sits on each GMC engine and the GM documents that name it.
• Cylinders 1, 4, 6 and/or 7 on a Sierra or Yukon V8 — those are GM's AFM cylinders. GM points to AFM lifters, not ignition.
• Cylinders 2 and/or 5 on a 2017-and-later Acadia or Canyon V6 — GM's AFM cylinders on the Gen 2 V6. GM points to the deactivation solenoids or the switching rockers.
• Every cylinder on bank 1 of a 2018 Sierra or Yukon — GM's PIP5642 traces this to a failing high-pressure fuel pump lifter. Knock activity retards timing on bank 1 by up to −16 degrees, which weakens the firing pulses enough to count misfires.
• Cylinder 1 on deceleration, or the far-end cylinder on hard acceleration, on an inline Canyon or Envoy — GM's PIP3472C blames contaminated fuel trapped in the returnless fuel rail.
• Random misfires on a Terrain 1.5T after a long highway drive in rain or humidity — moisture in the charge air cooler (22-NA-065).
• Only on a cold start, then gone — on a V6 Acadia, Terrain or Canyon, that's GM's coolant-in-the-cylinder pattern (18-NA-115). On a Sierra or Yukon V8 with P050D, see PIP5498M.
• Only on deceleration, every cylinder, on a V6 Acadia, Terrain or 2015 Canyon — GM's PIP5264 calls this a false misfire from belt or pulley debris or worn engine mounts.

What GM Has Documented on the Sierra, Yukon and Savana

AFM and DFM lifters

This is the big one on GMC trucks. PIP4568S covers the 2007–2013 Sierra, 2007–2014 Yukon and 2006–2009 Envoy with AFM. It describes misfires on cylinder 1, 4, 6 or 7, with or without a tick, from an AFM lifter that unlocks as soon as the engine starts or stays collapsed. GM's test is the AFM compression test: if the misfiring cylinder's running compression stays below 25 psi whether the AFM solenoid is commanded on or off, the lifter is the problem. For the 2014–2018 Sierra and 2015–2020 Yukon and Yukon XL with the 5.3L L83 or 6.2L L86, 15-06-01-002O continues the story: a collapsed or stuck AFM lifter, locking-pin damage from oil aeration, a lifter stuck in its bore, or a bent pushrod. If the valves don't move, GM replaces the valve lifter oil manifold and the affected bank of AFM lifters.

The DFM engines have their own documents. 23-NA-043 covers 2020 Sierra 1500 and 2021 Yukon trucks with the 5.3L L84 or 6.2L L87 built September 1, 2020 through March 31, 2021. GM's replacement rule depends on mileage: all lifters and guides on both banks under 16,000 miles, the affected bank only above that. PIP5861 applies the same rule to 2022 Sierra 1500 and Yukon trucks built October 9 through December 18, 2021.

Ignition, wiring and plug wires

PIP5159C (2014–2019 Sierra with the 4.3L, 5.3L or 6.2L, 2015–2019 Yukon) says to check for a plug wire that has come loose at the coil and to look for a missing "C" clip on the wire end. PIP5298B (2014–2019 Sierra Limited and 2015–2019 Yukon) points to poor terminal tension on the ignition coil power feed. On 2025 Sierra 1500 and Yukon trucks with the L84 or L87, PIP6073 blames a faulty ignition coil. GM tells technicians to swap the coil with a neighbor and warns that injectors returned to GM for this concern were found with no trouble.

Valve springs, coolant and recalls

PIP5752M covers 2020–2021 Sierra (L82, L84, L87, L8T) and 2021 Yukon (L84, L87) built July 1 through December 16, 2020, where a broken valve spring can bring misfire, noise and P0300 with P0106 or P0506. PIP5498M covers Sierra and Yukon trucks that set P050D and P0300 after a cold start because coolant is getting into the cylinders. GM's warning is that dealers were tearing engines down with no trouble found, so it asks for cold injector balance rates first. Safety recall 25V-274 covers certain 2021–2024 Sierra 1500, Yukon and Yukon XL trucks with the 6.2L V8 for connecting rod or crankshaft defects that can lead to engine failure. If your misfire comes with a knock, check that recall first.

One more truck document is worth knowing before you blame GM. PIP4765A (2007–2014 Sierra and Yukon V8s) describes no compression and 100% leakage into the crankcase from melted pistons. GM ties that to aftermarket calibrations and parts, and says it should not be treated as a warranty repair when they are found.

What GM Has Documented on the Acadia, Canyon and Terrain

3.6L V6, cold start. Bulletin 18-NA-115 (July 2024 version) names the Acadia (2007 onward), the 3.6L Canyon (2015 onward) and the 2010–2017 Terrain V6. GM describes a cold-start misfire "always occurring on one or two cylinders" that clears once the engine warms. The cause is porosity in the block at the liner-to-deck face, letting coolant in. GM's test is coolant dye, a pressure test on a cold-soaked engine, and a blacklight borescope through the plug hole.

Gen 2 V6. 21-NA-036 (2017–2022 Acadia LGX, 2017–2022 Canyon LGZ) covers P0300, P0302 and P0305 on AFM cylinders 2 and 5. The causes are oil leaking past the AFM oil control valve solenoid in the camshaft cover, or rockers that aren't latching. 21-NA-278 adds ticking or rattling with P0300–P0306 from spongy lash adjusters, damaged rockers or camshaft actuator damage.

Terrain turbo fours. 22-NA-065 covers 2018–2022 Terrain 1.5T models that set P0300, sometimes with a flashing light or Reduced Power, after long drives in rain or high humidity. Moisture collects in the charge air cooler and heavy acceleration pulls it into the engine. 21-NA-255 covers broken spark plug insulators on the same engine. PI1178F covers a cracked piston and low compression on the 2018 Terrain 2.0T.

Inline Canyon and Envoy. PIP4409F (2004–2012 Canyon 2.8L, 2.9L and 3.7L) describes history misfires on all cylinders, with codes such as P0106, P0171 or P0300. The cause is MAP sensor wiring broken inside the insulation within inches of the connector.

Symptoms of P0300 on a GMC

• Check engine light, flashing when the misfire is bad enough to damage the catalytic converter
• Rough idle, shake at a stop, or a stumble pulling away or towing
• Misfire only on a cold start, only under boost or load, or only after the truck leaves four-cylinder mode
• A tick at camshaft speed that doesn't go away when injectors are cancelled (lifter, rocker or valvetrain)
• Loss of power and fuel economy, a fuel smell, or Reduced Power on a Terrain turbo
• Companion codes: P050D, P0106/P0506 (valve spring pattern), injector circuit codes, or P0016–P0019 on the Gen 2 V6

Causes and How to Confirm Each

How Is P0300 Diagnosed on a GMC?

1. Identify the engine by RPO code from the glovebox label. A Sierra 1500 has been sold with a 4.3L V6, several 5.3L and 6.2L V8s and a 2.7L turbo four, and each has its own GM documents.
2. Save freeze frame and per-cylinder misfire counts before clearing anything. GM's Technical Assistance misfire template (PIP5628) asks dealers for exactly this.
3. Classify the pattern: one cylinder, AFM cylinders, one bank, cold start only, deceleration only, or weather-related.
4. Swap coils and plugs on the worst cylinder and re-test. Check plug wire seating on Gen V trucks.
5. Test injectors with GDS2 balance or AFIT instead of replacing them on suspicion.
6. Run compression and leak-down on any cylinder that won't respond. On an AFM truck, run GM's AFM compression test before pulling heads.
7. Run the engine-specific checks: valve movement on Sierra/Yukon lifters, the solenoid swap on the Gen 2 V6, the dye test on the 3.6L, the charge air cooler on the Terrain 1.5T.
8. Check your VIN for open recalls and bulletins, then verify the repair under the conditions that set the code.

Parts and Cost

GM Documents That List P0300 on GMC Models

Have a dealer check your VIN for open recalls, bulletins and special coverages. The check is free, and some GM documents apply only inside narrow build-date windows.

What Other Pages Get Wrong

• "P0300 means replace all the plugs and coils." On Sierras and Yukons, GM's most-repeated misfire bulletins are about lifters. Plugs won't fix a valve that isn't opening.
• "Unplug the AFM to cure it." GM's lifter bulletins describe lifters that are already collapsed or stuck. Disabling deactivation doesn't restore a damaged lifter.
• "Replace the injectors." GM's PIP6073 says injectors returned for the 2025 truck coil concern showed no trouble. GM asks for a failed balance or AFIT test first.
• Ignoring the weather. A Terrain 1.5T that misfires only after a rainy highway drive is a documented GM pattern, not a mystery.
• Treating "random" as random. GM's bulletins are organized by which cylinders count, so the counts are the most useful data you have.

Frequently Asked Questions

Can I drive my GMC with P0300?

If the check engine light is flashing, ease off and get it checked soon. A heavy misfire can overheat the catalytic converter, and a lifter or valve spring failure can get worse. A steady light with no felt misfire is less urgent, but it still needs diagnosis.

Why does my Sierra misfire only after it goes into V4 mode?

On AFM trucks, cylinders 1, 4, 6 and 7 deactivate under light load. A lifter that is slow to re-lock, or a damaged one, can misfire when the engine comes back to eight cylinders. GM's AFM compression test and valve-movement check are the way to confirm it.

Does P0300 apply to the Duramax?

This guide covers gasoline GMC engines. Duramax diesels use a different set of diagnostics, so follow the diesel service information for those trucks.

My Terrain flashed the check engine light in a rainstorm. Is the engine damaged?

Not necessarily. GM's 22-NA-065 describes 2018–2022 Terrain 1.5T misfires from moisture in the charge air cooler. A dealer will run the standard P0300 diagnosis first and apply the bulletin if nothing else is found.

Will a GMC dealer cover a lifter failure?

That depends on your vehicle's warranty status and build date. Some GM documents apply only to trucks built inside specific windows. A dealer can check your VIN for free.

What's the difference between P0300 and P0301–P0308?

P0300 means misfires were detected but spread out or not cleanly assigned. P0301 through P0308 name a single cylinder. Most GMCs set both at once, and the cylinder code tells you where to start.

Can a bad crankshaft sensor cause P0300?

The misfire monitor depends on crankshaft speed, so anything that disturbs that signal can create false counts. GM's PIP5264 for V6 Acadias and Terrains is an example: belt debris or worn mounts cause false deceleration misfires. See our P0335 GMC guide if a crank sensor code is also set.