P0301 Code on a Buick: Cylinder 1 Misfire Detected (Buick Guide)

P0301 on a Buick is "Cylinder 1 Misfire Detected." Unlike the random-misfire code P0300, it tells you exactly which cylinder the engine computer caught misfiring — and that makes it one of the most fixable codes there is, if you test before you buy. A coil swap takes minutes and tells you whether the fault follows the part or stays with the cylinder. The surprise on Buicks is what GM has documented when it stays with the cylinder: a coolant leak into the cylinder on 3.6L Enclave and LaCrosse V6 engines, damaged pistons on the 1.4L turbo Encore, and mis-installed rocker arms on the 2025 Enclave. GM's own bulletins list P0301 among the codes for each of those.

What Does P0301 Mean on a Buick?

Your Buick's engine computer (ECM) watches crankshaft speed through the crankshaft position sensor. Each time a cylinder fires, the crankshaft gets a small push. When cylinder 1 fails to fire properly, the crank slows for an instant at the moment cylinder 1 should have delivered its power stroke, and the ECM logs a misfire against cylinder 1.

Once the misfire count crosses GM's threshold, P0301 sets. If the misfires spread to other cylinders or move around, you will see P0300 as well — GM's misfire bulletins routinely list both together.

A misfire has only a few root causes:

• No spark, or weak spark — plug, coil, coil connector or wiring
• Wrong fuel — a clogged, leaking or electrically failed injector, or an injector wiring fault
• No compression — valves not sealing or opening, rings or piston damaged, head gasket
• Something in the cylinder that should not be there — coolant or oil

Because P0301 isolates a single cylinder, you can usually narrow it to one of those in a short series of tests. For random or multi-cylinder misfire, see our P0300 Buick guide.

Where Cylinder 1 Is on Your Buick

Before you swap anything, find the right cylinder. Getting this wrong is the most common way a P0301 repair goes sideways.

On a V6 or V8, P0301 together with P0303 and P0305 on a 3.6L — the other cylinders on bank 1 — is a different problem from P0301 alone. A whole-bank misfire points to something the bank shares, such as fuel trim on that bank or the valvetrain, rather than one coil.

The Coil Swap Test: Your First Five Minutes

On most Buick engines each cylinder has its own coil. That makes the classic test simple:

1. Record the codes and the misfire counts for each cylinder on a scan tool.
2. Swap the cylinder 1 coil with a neighboring cylinder's coil.
3. Clear the codes and drive under the conditions that set the code.
4. If the misfire moves to the other cylinder (P0303, for example), the coil is the fault. If it stays on cylinder 1, the coil is fine.

Repeat the same idea with the spark plug — move it to another cylinder and see if the misfire follows. If neither the coil nor the plug moves the misfire, the problem is in cylinder 1 itself: injector, wiring, compression, or something GM has documented below.

This test costs nothing and prevents the most common P0301 mistake: buying a full set of coils for a problem in one injector or one valve.

What GM Has Documented for Single-Cylinder Misfires on Buicks

We found no GM bulletin that is only about cylinder 1 on a Buick. But several GM bulletins covering Buick models list P0301 alongside P0300, and they describe faults that stay with one cylinder no matter what you swap.

3.6L V6: Coolant in the cylinder on a cold start

Bulletin 18-NA-115 covers the 2009–2025 Enclave, 2009–2019 LaCrosse, 2009–2011 Allure and 2018–2019 Regal V6 engines. GM describes a misfire on cold start "always occurring on one or two cylinders," with medium to high misfire counts, that goes away after the engine warms up. The cause is cylinder block porosity at the liner-to-deck face, letting coolant into the cylinder.

GM's test is coolant dye, a pressure test on a cold-soaked engine and a blacklight borescope through the spark plug hole. If verified, GM says the engine must be replaced.

The tell for a Buick owner: a P0301 that only shows up after the car sits overnight, with nothing wrong once warm, and a coil swap that does not move it.

1.4L turbo Encore: Low compression

Bulletin 18-NA-171 (2016–2019 Encore 1.4L LE2) lists P0301–P0304 as keywords. GM describes a rough-running engine, a misfire and low compression in one or more cylinders caused by a damaged piston. The procedure is a compression test followed by a cylinder leakage test; if leakage to the crankcase is found and the walls are undamaged, GM replaces all four pistons.

For 2013–2019 Encores with the 1.4L LUJ or LUV, 19-NA-090 describes the same pattern — misfire and low compression — caused by a broken piston ring land, often with oil consumption.

2025 Enclave 2.5L turbo: A valve that never opens

Bulletin 25-NA-102 lists P0301–P0304 as keywords. Rocker arms assembled incorrectly at the plant can leave a valve not opening. GM's check is a borescope in the spark plug bore while turning the engine by hand to confirm every valve moves.

Encore 1.4L: Crossed injector wiring

PIP5353A (2014–2017 Encore 1.4L) warns that fuel injector control circuits can be connected to the wrong injectors. Misfires then occur only under certain conditions or rpm and are hard to duplicate. If your Encore has had engine or harness work, compare the injector wire colors against the schematic.

Rainier 4.2L: Misfire only at idle

PIP4013D covers single-cylinder misfires that occur only at idle on the 2005–2007 Rainier with the 4.2L LL8 inline-six. GM points to a damaged valve, valve seat or piston ring, found by a cylinder leakage test with the shop air regulated to 50–60 psi.

Symptoms of P0301

• Check engine light on — flashing if the misfire is severe
• Rough idle or a rhythmic shake, especially at a stop
• Hesitation or stumble on acceleration
• Reduced power and fuel economy
• Misfire worst on a cold start (3.6L coolant-entry pattern) or only at idle (Rainier valve pattern)
• Fuel smell from the exhaust

Causes and How to Confirm Each

How Is P0301 Diagnosed on a Buick?

1. Confirm which cylinder is cylinder 1 on your engine using the GM cylinder diagram.
2. Record freeze-frame data — engine temperature, rpm and load at the time of the misfire. Cold-start-only and idle-only patterns point to specific GM bulletins.
3. Do the coil swap, then the plug swap, and see if the misfire moves.
4. Read the plug. Wet with coolant, oil-fouled or cracked each point in a different direction.
5. Check the injector and its circuit if spark is good.
6. Run a compression test, then a cylinder leakage test if compression is low.
7. On a 3.6L with a cold-start-only P0301, follow GM's 18-NA-115 dye and borescope procedure before replacing anything expensive.
8. Check your VIN for bulletins and recalls, then clear the code and verify under the original conditions.

Parts and Cost

Buy the coil the test points at, not a set of six. Order by VIN — Buick engines use different coils and plugs, and the same model name can carry more than one engine.

GM Documents That List P0301 on Buick Models

Have a dealer check your VIN against current bulletins rather than relying on any article, including this one.

What Other P0301 Pages Get Wrong

• "Replace all the coils." P0301 names one cylinder. A coil swap proves whether the coil is at fault before you spend anything.
• "Cylinder 1 is always at the front." On a transverse 3.6L Buick, cylinder 1 is on bank 1 — the rear, firewall-side bank. Check the diagram.
• "If the coil and plug are good, it's the injector." On Buick engines GM has documented coolant entry, damaged pistons and valves not opening — a compression and leakage test belongs in the sequence.
• "A cold-start misfire that clears up is nothing." On the 3.6L V6 that is the exact pattern GM describes for block porosity.
• Ignoring the plug's condition. A plug wet with coolant on a 3.6L tells you more than any code reader.

Frequently Asked Questions

Can I drive with P0301?

Short distances with a steady light, usually. A flashing light means a severe misfire that can damage the catalytic converter — get it checked promptly, and avoid heavy loads.

Which coil is cylinder 1 on my Enclave?

Cylinder 1 is on bank 1, which on the transverse 3.6L Enclave is the rear, firewall-side bank. Use the cylinder diagram in GM service information to pick the exact coil.

Why does P0301 come back after new plugs?

Because the plug was not the fault. Do the coil swap, check the injector, and run a compression test. On a 3.6L Buick with a cold-start-only misfire, ask about GM bulletin 18-NA-115.

Is P0301 the same as P0300?

No. P0301 isolates cylinder 1; P0300 is random or multi-cylinder misfire. They often appear together because GM's monitor logs both when one cylinder is very active.

Can a vacuum leak cause P0301?

It can if the leak is close to cylinder 1's intake runner, but vacuum leaks more often cause random misfire across several cylinders.

Does a low compression reading mean a new engine?

Not automatically. On Encore 1.4L engines GM's bulletins replace pistons and rings when the cylinder walls are undamaged. On the 3.6L V6, coolant entry from block porosity is the case where GM calls for engine replacement.