P0302 – Cylinder 2 Misfire Detected

Last updated: April 2, 2026

P0302 means the engine misfired on cylinder 2. You will usually feel shaking at idle, a stumble on acceleration, or a flashing MIL that warns of possible catalytic converter damage. The PCM (engine computer) does not “see” a bad part. It detects that cylinder 2 contributes less torque than expected during combustion. This is an ISO/SAE standardized OBD-II code, and it carries the same definition across manufacturers: Cylinder 2 Misfire Detected. The real job now is to prove whether the cause is spark, fuel, air, compression, or a control issue.

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P0302 Quick Answer

P0302 points to a misfire on cylinder 2, not a guaranteed bad coil or plug. Start by confirming the misfire in Mode $06 or live misfire counters, then verify ignition, injector operation, and cylinder compression on that hole.

What Does P0302 Mean?

P0302 meaning: the PCM detected a misfire event rate on cylinder 2 high enough to set a code. In practice, cylinder 2 does not burn the mixture consistently, so the engine runs rough and loses power. You may also see increased fuel smell, poor mileage, and catalyst overheat risk if the misfire continues.

Technically, the PCM infers misfire by monitoring crankshaft speed changes and firing order timing. Each firing event should slightly accelerate the crank. When cylinder 2 fires weakly or not at all, the PCM measures an abnormal deceleration pattern at that crank angle and assigns it to cylinder 2. That matters because the code only identifies the suspect cylinder. Diagnosis must confirm whether the fault comes from ignition, fueling, air leakage, mechanical compression, or wiring control.

Theory of Operation

Under normal operation, the PCM commands fuel injection and ignition timing for each cylinder. The plug ignites the air-fuel charge, cylinder pressure rises, and the crank speeds up in a predictable pattern. The PCM uses crankshaft position data to track those small speed changes and calculates misfire “counts” by cylinder.

P0302 sets when cylinder 2 repeatedly fails to contribute normal torque. Common breakdowns include weak spark under load, a cylinder-specific fuel delivery problem, or a mechanical issue like low compression. Air leaks near cylinder 2 can also lean out that runner and create a miss. The PCM cannot tell which one happened, so you must test the inputs and outputs that make cylinder 2 fire.

Symptoms

P0302 symptoms usually show up as a noticeable driveability problem, especially at idle and during tip-in acceleration.

• Flashing MIL: the check engine light may flash during the misfire, especially under load
• Rough idle: the engine shakes or “loping” idle appears, often worse in gear
• Hesitation: the vehicle stumbles on acceleration or feels flat on a hill
• Vibration: steering wheel or vibration increases at specific RPM ranges
• Fuel smell: unburned fuel odor from the exhaust may appear after a cold start
• Poor fuel economy: mileage drops because the PCM adds fuel to compensate
• Hard start: extended cranking can occur if the miss is severe or intermittent

Common Causes

• Cylinder 2 ignition secondary leak (boot, wire, or coil tower): Spark escapes to ground under load, so cylinder 2 fails to ignite the mixture and the PCM flags a misfire.
• Faulty spark plug on cylinder 2 (fouled, cracked, wrong gap, wrong heat range): A weak or inconsistent spark delays combustion and creates the crankshaft speed change pattern used to set P0302.
• Coil-on-plug (or coil pack) output problem affecting cylinder 2: Low coil energy or intermittent coil breakdown causes a repeatable cylinder-specific misfire without requiring any other cylinders to misfire.
• Injector problem on cylinder 2 (electrical, clogging, or leakage): A restricted injector leans that cylinder, while a leaking injector floods it; either condition destabilizes combustion and triggers P0302.
• Cylinder 2 compression or mechanical sealing issue: Low compression from a valve, ring, or head gasket concern reduces burn quality and produces a steady misfire signature at certain loads.
• Vacuum or intake air leak localized near cylinder 2: Unmetered air at a runner or gasket leans one cylinder more than the others, so misfire counts concentrate on cylinder 2.
• Wiring or connector issue at coil #2 or injector #2: High resistance, spread terminals, or corrosion drops available current and creates intermittent loss of spark or fuel on that cylinder.
• Fuel quality or fuel pressure delivery problem that shows up first on cylinder 2: Low fuel pressure or contaminated fuel can push one marginal cylinder into misfire before others, especially at idle or tip-in.
• Engine control module driver or control issue (rare): A failing coil or injector driver can interrupt control to cylinder 2, but you must prove power, ground, and commanded control before condemning the module.

Diagnosis Steps

Tools: a capable scan tool with Mode $06 misfire data, a digital multimeter, a fuel pressure gauge when applicable, and a wiring diagram. A lab scope helps confirm coil and injector patterns fast. Use basic hand tools for plug and coil access. Plan for a road test to capture a scan tool snapshot under the same load.

1. Confirm P0302 and note if it is pending or confirmed/stored. Record freeze-frame data, especially RPM, engine load, coolant temperature, fuel system status (open/closed loop), STFT/LTFT, and vehicle speed. These values tell you if the misfire occurs at idle, cruise, or under load.
2. Check for related DTCs first. Address fuel trim codes, crank/cam correlation codes, or coil/injector circuit codes before chasing a cylinder misfire. If P0302 only shows as pending, treat it as an intermittent and prioritize connector and pattern checks.
3. Review Mode $06 misfire counters and misfire history by cylinder. Verify cylinder 2 leads the count, not just the current DTC label. Use a scan tool snapshot during a drive to capture live misfire data when the stumble occurs; freeze frame shows when the code set, while a snapshot catches intermittent events.
4. Verify power distribution to ignition and injection. Check the relevant fuses and relays, then verify B+ feed at the coil/injector supply circuit with the engine running. A fuse can test good visually and still drop voltage under load.
5. Load-test grounds and power feeds with voltage-drop testing. With the circuit operating, measure ground drop from the coil/injector ground reference to battery negative and keep it under 0.1 V. Next, measure power-side drop from battery positive to the component feed while it runs; excessive drop points to high resistance in a fuse, relay, splice, or connector.
6. Perform a targeted visual inspection at cylinder 2. Look for oil or coolant in the spark plug well, carbon tracking on the boot, a loose coil hold-down, rubbed-through harness near brackets, and spread or corroded terminals. Fix obvious connection problems before any parts swapping.
7. Check the spark plug condition and compare it to an adjacent cylinder. Inspect for wet fuel, heavy carbon, cracked porcelain, and incorrect gap. If the plug looks abnormal, verify the root cause (fueling, oil control, coolant intrusion) instead of only replacing the plug.
8. Isolate ignition faults with a controlled swap test when the design allows it. Swap coil #2 with another cylinder and move the plug if practical, then clear codes and recheck misfire counters. If the misfire follows the moved part, you confirmed a component-related issue rather than a cylinder-specific mechanical problem.
9. Test injector #2 operation and its circuit. Use a stethoscope for clicking, then verify injector feed voltage and PCM control with a noid light or scope. If electrical control looks normal, perform an injector balance or flow comparison when equipment and access allow.
10. Check for air leaks that bias cylinder 2. Inspect the intake runner gasket area, PCV hoses, brake booster hose, and any vacuum ports near that runner. Use smoke testing if available, since small leaks can create a cylinder-specific lean misfire without a global lean code.
11. Verify mechanical integrity if ignition and fueling checks pass. Perform a compression test on all cylinders, then use a leak-down test to pinpoint valve, ring, or head gasket issues. Compare cylinder 2 to the others; an outlier explains why the PCM consistently reports P0302.
12. Confirm the repair. Clear codes, then road test under the freeze-frame conditions and watch live misfire counters and fuel trims. Make sure the misfire monitor runs without new counts, and verify readiness monitors complete after clearing codes.

Professional tip: Don’t trust a quick continuity check on coil or injector grounds. High resistance often hides until the circuit carries current. Voltage-drop testing under load finds the real problem and prevents repeat misfire comebacks.

Possible Fixes

• Repair wiring damage or terminal tension issues at coil #2 or injector #2, then verify low voltage drop under load.
• Clean, reseat, or replace contaminated ignition components on cylinder 2 (spark plug, boot, or coil) only after confirming power/ground integrity.
• Correct a localized vacuum leak at the intake runner gasket, hose connection, or PCV plumbing near cylinder 2.
• Restore proper fuel delivery by correcting fuel pressure issues or servicing injector #2 after confirming command and feed circuits.
• Repair mechanical engine faults affecting cylinder 2 after compression and leak-down testing confirms a sealing problem.
• Update or replace the PCM only after proving correct inputs, solid power/grounds, and a verified driver fault with test equipment.

Can I Still Drive With P0302?

You can sometimes drive short distances with a P0302 code, but you should treat it as a “get it diagnosed now” fault. A cylinder 2 misfire can turn into a flashing MIL under load, which means the engine risks catalyst damage. If the engine shakes at idle, stumbles on acceleration, or the MIL flashes, stop driving and tow it. Raw fuel from a hard misfire overheats the catalytic converter and can melt it. Avoid heavy throttle, high speeds, and towing. If the misfire feels mild and steady, drive only to a safe repair location and keep RPM low.

How Serious Is This Code?

P0302 ranges from an inconvenience to a repair that gets expensive fast. A light, intermittent misfire may only cause a rough idle and reduced fuel economy. A frequent or load-related misfire can cause stalling, unsafe merging power, and catalyst damage. A flashing check engine light signals a severe misfire event, and you should shut the engine off as soon as it is safe. Long-term driving with P0302 can foul oxygen sensors, damage the catalytic converter, wash oil off the cylinder wall, and dilute engine oil with fuel. Treat recurring P0302 as high priority.

Common Misdiagnoses

Many shops replace spark plugs or the coil pack first and never confirm cylinder 2 misfire counts. That approach misses wiring faults at the coil or injector connector, and it wastes parts. Another common mistake involves swapping parts without checking fuel trim and vacuum leaks that skew mixture on one bank. Technicians also overlook mechanical causes like low compression, leaking valves, or a head gasket seep that affects one cylinder. DIY owners often clean the throttle body and call it fixed after clearing codes. The misfire returns because the root cause remains and OBD-II misfire monitoring needs drive time to prove the repair.

Most Likely Fix

The most common confirmed P0302 repair path starts with verifying ignition output on cylinder 2 and proving the wiring can carry current under load. Many vehicles end up needing a coil, plug, or a coil connector/pigtail repair after a voltage-drop test shows excessive resistance. The next frequent direction involves fuel delivery to cylinder 2. A restricted injector, poor injector power feed, or a driver control issue can create a lean misfire on that cylinder. Confirm each possibility with misfire counters, a cylinder balance test, and targeted circuit checks before you replace parts.

Repair Costs

Repair cost depends on whether the confirmed root cause is wiring, connector condition, a sensor, a module, or the labor needed to diagnose the fault correctly.