P0302 Code: Cylinder 2 Misfire Detected

P0302 — Cylinder 2 Misfire Detected: What It Means and How to Fix It

A P0302 code means the powertrain control module (PCM) has detected a misfire specifically in cylinder number two. It is not a generic misfire — it is pinned to one cylinder, which is both good news and bad news. The good news is you already know where to look. The bad news is that a cylinder-specific misfire can be caused by ignition, fuel, or mechanical problems, and you still have to sort out which one you are dealing with before you start throwing parts at it.

This article walks through exactly how the PCM catches a misfire, why that matters for your diagnosis, and how to work through the three categories of causes in a logical order so you are not wasting time or the customer's money.

How the PCM Detects a Misfire

The PCM does not have a misfire sensor. What it has is a crankshaft position sensor, and it uses that sensor to detect misfires indirectly through a method called crankshaft deceleration monitoring.

Here is how it works. Every time a cylinder fires correctly, the combustion event pushes the piston down and accelerates the crankshaft slightly. The PCM reads the timing signal from the reluctor wheel on the crank and calculates the rotational velocity between each tooth. When a cylinder misfires, that acceleration event does not happen. Instead, the crankshaft decelerates slightly during that firing interval. The PCM compares the rotational speed across all cylinders and when it sees that one interval consistently comes up short, it flags the corresponding cylinder.

This is why cylinder-specific codes like P0302 are more useful than a P0300 random misfire. With P0300, the PCM is seeing misfires scattered across multiple cylinders or cannot consistently pin the deceleration event to a single cylinder — which often points to a system-level problem like low fuel pressure, a vacuum leak, or a timing issue. With P0302, the deceleration is happening consistently at the cylinder 2 firing interval. That narrows your field considerably.

The PCM also tracks misfire rate. A low misfire rate that stays below the catalyst damage threshold will store a P0302 as a pending code and may not illuminate the MIL right away. A higher misfire rate — typically over 2 percent of firing events in a given window — will set a confirmed code and light the MIL. A severe misfire rate that the PCM calculates could damage the catalytic converter will trigger a flashing MIL. If you see a flashing check engine light, treat it seriously. Continued driving with a severe misfire can overheat and destroy a converter, and that repair cost will dwarf whatever caused the misfire in the first place.

Why Cylinder 2 Specifically

Before you chase causes, confirm the cylinder numbering for the vehicle you are working on. Cylinder 2 is not always in the same physical location. On most inline four-cylinder engines, cylinder 1 is on the timing chain or belt end, and cylinder 2 is the next one toward the firewall. On V6 and V8 engines, the numbering convention varies by manufacturer. GM V8s typically number odd cylinders on the driver's side and even cylinders on the passenger's side, so cylinder 2 is at the front of the passenger's side bank. Ford modular V8s number front-to-back on the passenger's side first, making cylinder 2 the second from the front on the passenger's side bank. Chrysler Hemi engines number differently again. Look it up for the specific engine before you start probing the wrong component.

Getting cylinder numbering wrong is one of the most common ways techs waste an hour on a misfire diagnosis. Pull up the factory service data, confirm the firing order and cylinder location, and then proceed.

Category One: Ignition Causes

Ignition problems are the most common cause of a cylinder-specific misfire, and they are also the easiest to confirm or rule out because the components are swappable. Start here.

Coil-on-Plug or Coil Pack

On modern engines with coil-on-plug (COP) ignition, the coil sits directly on top of the spark plug. When a COP coil fails, it affects only the cylinder it serves — which is exactly the pattern you see with P0302. The coil may fail internally with an open or shorted winding, or it may develop a crack in the boot that allows the high-voltage arc to track to ground instead of jumping the plug gap.

The swap test is your best friend here. Move the cylinder 2 coil to a different cylinder — cylinder 3 or 4 is fine — and clear the codes. Drive the vehicle through a misfire monitor cycle. If the misfire code follows the coil to its new location (you get P0303 or P0304 instead of P0302), the coil is bad. If P0302 comes back and stays on cylinder 2, the coil is fine and you move on.

On older engines with a coil pack that serves multiple cylinders, test the secondary resistance across the towers and compare to spec. A coil pack failure affecting only one output tower is less common but it happens, especially on Ford 4.6L and 5.4L three-valve engines where the coil boots deteriorate and cause arcing.

Spark Plugs

Pull the cylinder 2 spark plug and inspect it. A worn plug with an eroded electrode and excessive gap will misfire under load. A fouled plug — oil fouling appears as wet, black, and oily; carbon fouling appears as dry and sooty — tells you something about what is going on inside the combustion chamber. A cracked insulator can cause a misfire that is intermittent and hard to reproduce on the lift.

Compare the cylinder 2 plug to the other cylinders. If all the other plugs look healthy and cylinder 2 looks different, that is telling you something. Also note that if you find a severely fouled plug and just replace it, the misfire may come back if you have not addressed what caused the fouling in the first place.

Plug Wires

Distributorless and COP systems do not use traditional plug wires, but if you are working on an older engine with a distributor and wire set, test the cylinder 2 wire resistance. High resistance from a deteriorated wire core will cause a misfire under load that may not show up at idle. Use an oscilloscope on the secondary ignition if you have one — you will see a suppressed firing line, a shortened spark duration, or erratic waveform on a failing wire.

Ignition Module and Crankshaft/Camshaft Position Sensors

If swapping the coil does not move the misfire and the plug looks good, check the control side of the ignition circuit. Scope the coil driver signal at the cylinder 2 coil connector. You should see a clean, consistent trigger signal from the PCM. If the signal is missing or erratic only on that cylinder's driver circuit, suspect the PCM output driver or wiring between the PCM and the coil. Open circuits, chafed wires, and corroded connectors can cause a cylinder-specific misfire that looks like a coil or plug problem until you check the signal.

Category Two: Fuel Causes

If ignition checks out, move to fuel. Fuel-related misfires can be cylinder-specific when an individual injector is the problem, but they can also appear on a single cylinder when a broader fuel delivery issue affects one cylinder more than others due to its position in the intake manifold.

Injector Failure

A fuel injector can fail in two directions. It can fail lean — not delivering enough fuel due to a clogged tip, weak spray pattern, or electrical failure. Or it can fail rich — leaking fuel past a worn needle and seat, causing a flooded condition at idle. Both cause misfires, but they look different on a scan tool. A lean misfire from a clogged injector will often worsen under load. A rich misfire from a leaking injector will often be worst at cold start and idle, and the cylinder 2 oxygen sensor may show a rich bias.

Use a scan tool with fuel injector balance test capability if available. This test drops each injector in sequence and measures the RPM drop. A cylinder with a restricted injector will show a smaller RPM drop than the others. Some scan tools will also allow you to look at individual injector pulse width and fuel trim corrections on a per-cylinder basis on engines that support it.

You can also listen to the injectors with a stethoscope. A functioning injector makes a consistent click at idle. An injector that is electrically dead will be silent. Pull the injector connector and verify you have power and a proper trigger signal before condemning the injector itself.

Injector Circuit Problems

Just like the ignition side, the injector circuit can have wiring problems that cause a cylinder-specific issue. Check for power at the injector connector with the key on. Verify the ground path — on some applications the PCM controls the injector on the ground side, and a bad PCM driver can cause one injector to stop firing. Back-probe the injector connector and watch the trigger signal on a scope or graphing meter during cranking to confirm the PCM is commanding the injector to open.

Low Fuel Pressure Affecting One Cylinder

Fuel pressure that is low across the board typically causes a random misfire or a lean condition across multiple cylinders. However, on returnless fuel systems with a port fuel injector at the end of the fuel rail, that last injector in the rail may see slightly lower pressure if the rail itself has a restriction or if the regulator is marginal. Cylinder 2 is not always at the end of the rail, but it is worth noting as a factor on some platforms. Connect a fuel pressure gauge and monitor pressure at idle and under load. A snap-throttle test that shows pressure dropping and not recovering quickly points to a pump that is too weak.

Category Three: Mechanical Causes

Mechanical causes are the most serious and typically the most expensive. They should be confirmed after ignition and fuel have been ruled out, or when the clinical picture — high mileage, coolant consumption, oil burning, overheating history — points in that direction from the start.

Compression Loss

A compression test is the starting point for mechanical diagnosis. Crank the engine with the ignition disabled and fuel pump disabled, and test cylinder 2 compression. Compare it to the other cylinders and to the manufacturer's specification. A low reading on cylinder 2 relative to the others confirms a mechanical problem exists. It does not tell you where — you need a leak-down test for that.

Cylinder Leak-Down Test

A leak-down test pressurizes the cylinder through the spark plug hole with the piston at top dead center on the compression stroke, then measures how much air leaks past the rings, valves, or head gasket. Listen for where the air is escaping. Air coming out the oil fill opening points to worn rings or a scored cylinder wall. Air escaping into the intake indicates a burnt or leaking intake valve. Air out the exhaust points to an exhaust valve problem. Bubbles in the coolant overflow tank or a sweet smell from the leak-down test indicates a head gasket leak. A cylinder with more than 20 percent leak-down is typically considered problematic, though some manufacturers have tighter specifications.

Valve Train Problems

A burnt exhaust valve is a classic cause of a cylinder-specific misfire that does not respond to coil or plug replacement. The valve may seal well enough to build some compression but leak enough to cause a misfire under load. Variable valve timing problems can also cause cylinder-specific misfires, particularly on engines where the VVT system controls individual cylinders or banks. Carbon buildup on intake valves — especially common on GDI engines — can restrict airflow to cylinder 2 specifically if the intake port or valve is particularly dirty.

Head Gasket Failure

A head gasket failure at cylinder 2 can cause a misfire in several ways. It can allow coolant into the combustion chamber, which will foul the plug and suppress combustion. It can allow combustion gases to escape into the cooling system, which you can detect with a block test (combustion gas test) on the coolant overflow. It can allow oil to enter the cylinder. A cylinder 2 head gasket failure is sometimes localized — the rest of the engine may look perfectly fine — so a normal cooling system pressure hold does not always rule it out. Perform the block test and check for hydrocarbons in the coolant before you close out the mechanical diagnosis.

Timing Chain or Belt Issues

A stretched timing chain or worn tensioner can cause a cam timing deviation that affects all cylinders, but the first misfire code to appear is often on a specific cylinder because the cam timing error is larger at one point in the rotation. If you have a P0302 with no obvious ignition or fuel cause, and the engine has high mileage or you can hear a timing rattle on cold start, pull the cam timing data on a scan tool. Many scan tools will display cam phaser position relative to commanded position. An actual-to-commanded deviation outside of spec points to a timing chain or tensioner problem.

GDI Engines and Carbon Buildup

Gasoline direct injection engines do not wash the intake valves with fuel the way port-injected engines do. Over time, carbon deposits accumulate on the intake valves, and some cylinders will accumulate more than others depending on their position, the EGR routing, and the PCV system design. Cylinder 2 on some GDI engines is particularly prone to heavy carbon buildup. A P0302 on a GDI engine with 80,000 or more miles on it — especially a BMW N20, Audi 2.0T, or Hyundai 2.0 Theta II — should trigger a walnut blast or chemical induction cleaning as part of the diagnostic workup. Pull the intake manifold if necessary and inspect the valve heads directly. A cylinder with a valve choked with carbon deposits will misfire under load even with perfect ignition and fuel delivery.

Common Vehicles with Known Cylinder 2 Issues

Vehicle	Engine	Common Cylinder 2 Cause
Ford F-150 / Mustang GT	5.4L 3V Triton	COP boot failure, stuck coil to plug, spark plug ejection
GM 5.3L / 6.2L Gen IV LS	LS-based V8	AFM lifter collapse on cylinder 2 (passenger front), oil consumption
BMW N20 / N26 2.0T	Turbocharged 4-cyl GDI	Carbon buildup on intake valves, timing chain tensioner
Honda 2.4L K24	i-VTEC inline 4	Injector failure, spark plug wear at high mileage
Dodge 5.7L / 6.4L Hemi	Hemi V8	MDS (cylinder deactivation) lifter failure, spark plug fouling
Hyundai / Kia 2.0L Theta II GDI	Turbocharged GDI	Carbon deposits, oil consumption, bearing failure
Toyota 3.5L 2GR-FE / FKS	V6	Coil failure, injector leak on direct injection variant

Relative Compression Using a Scan Tool

You do not always need to pull spark plugs to get a quick read on mechanical condition. Many professional scan tools and some OEM tools support a relative compression test. This test cranks the engine with fuel and ignition disabled and reads the crankshaft acceleration pattern during cranking — the same deceleration method the PCM uses during running. A cylinder with low compression will show less crankshaft acceleration during its compression stroke than the healthy cylinders.

Relative compression testing is not a replacement for a traditional compression test with a gauge, but it is a fast screening tool that can confirm a mechanical problem is present before you start pulling components. If cylinder 2 shows a significantly lower relative compression value than the other cylinders during a cranking test, you have strong evidence of a mechanical issue and can proceed directly to a leak-down test.

The Diagnostic Sequence That Actually Works

1. Confirm the code is current. Check freeze frame data — note RPM, load, coolant temp, and whether the misfire occurred at idle, cruise, or under load. This gives you clues about the cause.
2. Identify cylinder 2's physical location for this specific engine. Do not guess.
3. Perform the coil swap test if the engine uses COP ignition. Move the cylinder 2 coil to another cylinder, clear codes, drive, and see if the misfire follows.
4. Pull the cylinder 2 spark plug. Inspect it. Replace it if worn or fouled. Note what the fouling pattern tells you.
5. If ignition is clear, perform an injector balance test or listen and test the injector circuit. Check fuel pressure.
6. If ignition and fuel are clear, perform a compression test and follow with a leak-down test if compression is low or borderline.
7. On GDI engines with high mileage, inspect for carbon buildup and check cam timing data before concluding.
8. Document your findings and present a repair plan before authorizing parts. A P0302 has a short list of causes — work through it systematically and you will find it.

Clearing the Code and Verifying the Repair

After the repair, clear the DTC and run the vehicle through a misfire monitor drive cycle. On most vehicles this means driving at moderate load — light to medium acceleration, highway speeds, and some city driving — until the PCM completes its monitor. Use a scan tool to watch the misfire counter for cylinder 2 in real time. If the counter stays at zero through the drive cycle, the repair is confirmed. If misfires are still accumulating, even slowly, you have not fixed the root cause yet and need to go back through the diagnostic sequence.

Do not let a customer leave with a P0302 unresolved if the misfire counter is still active. A low-grade misfire will eventually damage the catalytic converter, and that repair will come back to haunt either the shop or the customer depending on how the repair was documented.