P0302
- Powertrain
- Generic (SAE)
- Emissions
Get it looked at now
Unburned fuel and oxygen dumped into the catalytic converter can overheat and melt it, and a flashing MIL means that is happening right now. Even a steady MIL misfire loses power, can hesitate when pulling into traffic, and typically gets worse rather than better. Cylinder-specific misfire also occasionally signals a mechanical failure such as a burnt valve.
- Safe to drive
- Flashing light means pull over safely and stop driving. Steady light with rough running: drive gently, short distance, straight to a shop.
Cylinder 2 Misfire Detected
The computer detected that cylinder 2 is not producing its share of power on a repeated basis. It knows which cylinder is failing but not why, and the cause is nearly always spark, fuel or compression at that one cylinder.
The ECM measures crankshaft acceleration between firing events using the crank sensor and reluctor wheel. A cylinder that fails to burn its charge produces a measurable deceleration at its position in the firing order, which the ECM attributes to that cylinder. A single-cylinder code points first at components dedicated to cylinder 2 and at that cylinder's mechanical condition. It does not completely exclude a shared cause: marginal fuel pressure, a central vacuum leak or a common mechanical condition often shows up on the weakest cylinder first, which is why the misfire counters on every cylinder should be read before the diagnosis is narrowed.
How the car detected itMisfire monitoring runs two counters. A fast counter over roughly 200 crank revolutions catches misfire severe enough to damage the catalyst and triggers a flashing MIL. A slower counter over roughly 1000 revolutions catches misfire that merely exceeds emissions limits and sets a steady MIL. The rate is calculated per cylinder, which is why the code names cylinder 2 specifically. Some ECMs will disable the injector on a badly misfiring cylinder to protect the converter.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Flashing light means pull over safely and stop driving. Steady light with rough running: drive gently, short distance, straight to a shop.
- Urgency
- Get it looked at now
- Will it pass emissions
- No
- If ignored
- A misfiring cylinder pumps raw fuel into the exhaust. Sustained, that overheats the catalytic converter until the substrate melts, which restricts the exhaust and can leave the car barely able to move. Unburned fuel also washes oil off the cylinder wall and dilutes the crankcase oil. If the underlying cause is a burnt valve or failing head gasket, continuing to drive turns a repairable condition into head work.
- Check engine light
- Solid
- Clearing the light
- A completed drive cycle is normally required before the monitor re-runs and the light can clear.
- Check engine light on or flashing
- Rough idle and uneven running
- Power loss, hesitation under acceleration
- Increased fuel consumption
- Possible smell of unburned fuel from exhaust
Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.
These are the causes this code can have. For the order to work through them in, see what to check first.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Ignition coil for cylinder 2 failed | Very common | — |
| 2 | Spark plug for cylinder 2 worn or fouled | Very common | — |
| 3 | Cylinder 2 injector clogged | Common | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
In order. Each of these is cheaper or faster than what follows it, and each one can make the rest unnecessary.
Whether the check engine light is flashing or steady
This is the single most important observation. Flashing means catalyst-damaging misfire is happening right now and the car should not be driven.
Freeze frame data: rpm, load, coolant temperature and fuel trims when the code set
A misfire only when cold points to a different set of causes than one only under load. It tells you how to reproduce the fault instead of guessing.
Which physical cylinder is number 2 on this engine
Cylinder numbering and layout vary by manufacturer, especially on V engines where cylinder 2 can sit on either bank. Pulling the wrong coil is a wasted hour.
Misfire counters for all cylinders on live data
If cylinder 2 dominates but neighbors also show counts, the fault may be shared or the coil may be arcing to an adjacent plug. Counts spread evenly across cylinders point away from a single-cylinder cause.
Service history for spark plugs
Plugs at or past their replacement interval make cylinder 2 the first one to give up. A due plug set is both the likely cause and the cheapest test.
Confirm and characterize the misfire
Tools Scan tool with misfire counter PIDs
With the engine running, watch per-cylinder misfire counts on live data and note whether the misfire is at idle, under load, cold only, or constant. Reproduce the freeze frame conditions.
ExpectedCounts concentrated almost entirely on cylinder 2 confirm a single-cylinder fault. Meaningful counts on other cylinders reopen the possibility of a shared cause such as fuel pressure or a central vacuum leak.
Swap the cylinder 2 ignition coil to another cylinder
Tools Basic hand tools, scan tool to clear and re-read codes
Move the coil from cylinder 2 to a cylinder that is running well, clear the codes, and run the engine until the misfire returns. This is the fastest definitive test on the code and costs nothing.
ExpectedIf the code follows to the other cylinder, the coil is the fault. If it stays on cylinder 2, the coil is good and the problem is the plug, injector or the cylinder itself.
Remove and read the cylinder 2 spark plug
Tools Spark plug socket, gap gauge, feeler gauge
The plug is a written record of what happens in that cylinder. Compare it directly against a plug from a healthy cylinder. Check the gap and look for cracks in the insulator and carbon tracking down the ceramic.
ExpectedLight tan or gray and dry. Black and sooty means rich or weak spark, oily means valve seals or rings, wet with fuel means no ignition, white and blistered means lean or overheating, coolant-clean means a possible head gasket leak.
Swap the plug and confirm the result
Tools Spark plug socket, torque wrench
If the coil test was negative, move the cylinder 2 plug to a healthy cylinder and vice versa. If the misfire follows the plug, replace the plugs as a set rather than singly.
ExpectedMisfire following the plug confirms the plug. Misfire staying with cylinder 2 escalates to injector or compression.
Test the cylinder 2 injector
Tools Mechanic's stethoscope or noid light, digital multimeter
Listen for a clean, crisp click with a stethoscope, measure winding resistance and compare it to the other injectors on the engine, and check that the ECM is actually driving it. On port injection an injector can also be swapped with a neighbor to see if the misfire follows.
ExpectedAll injectors clicking evenly, with resistance closely matched across the set. Exact resistance values vary by engine, so compare rather than trusting a generic number.
Check the coil circuit rather than only the coil
Tools Digital multimeter, oscilloscope or noid light
Verify battery voltage at the coil connector with the key on, check the ground, and confirm the ECM is delivering a trigger signal. A corroded terminal or a failed driver in the ECM produces the same symptom as a bad coil, and swapping coils will not reveal it.
ExpectedSolid supply voltage, clean ground, and a switching trigger signal present while cranking or running.
Run a compression and leak-down test on cylinder 2
Tools Compression gauge, leak-down tester, compressed air
If the misfire stays with the cylinder through coil, plug and injector swaps, the problem is mechanical. Compare cylinder 2 to its neighbors, then leak-down test and listen for where the air escapes: intake, exhaust, crankcase or the adjacent cylinder.
ExpectedCylinders within roughly 10 to 15% of each other. Air heard at the tailpipe indicates an exhaust valve, at the intake an intake valve, at the oil filler the rings, and bubbles in the coolant a head gasket.
Look for a leak or restriction local to cylinder 2
Tools Smoke machine, inspection light
Check that runner's intake gasket and any vacuum port serving it, and inspect for an oil leak filling the plug tube. Oil pooling in a plug well shorts the coil boot and produces a stubborn single-cylinder misfire that returns after new parts.
ExpectedDry plug wells and no smoke escaping around that runner.
| Repair | Only after you confirm | Typical cost | Who |
|---|---|---|---|
| Replace the ignition coil for cylinder 2 | The misfire following the coil when it is swapped to another cylinder | $130–$400 | DIY |
| Replace the spark plugs as a set | The misfire following the plug on a swap, or a worn, cracked or fouled plug found on inspection | $90–$450 | DIY |
| Clean or replace the cylinder 2 fuel injector | No click, resistance out of line with the other injectors, or the misfire following the injector on a swap | $180–$650 | Hard |
| Repair coil wiring, connector or ground | Missing supply voltage, a bad ground, or no trigger signal at the cylinder 2 coil connector | $100–$350 | DIY |
| Replace the valve cover gasket and spark plug tube seals | Oil found pooled in the cylinder 2 spark plug well | $180–$650 | DIY |
| Repair a vacuum leak at the cylinder 2 intake runner or injector seal | Smoke escaping at that runner or seal under a smoke test | $150–$700 | DIY |
| Cylinder head repair for a burnt or leaking valve | Low compression on cylinder 2 with leak-down air audible at the intake or exhaust | $1,200–$4,000 | Shop |
| Head gasket replacement | Low compression with bubbles in the coolant, or combustion gases detected in the cooling system | $1,400–$3,500 | Shop |
US independent-shop ranges, parts plus labor. Most of these end at the coil or plug end of the list. Plug replacement cost depends almost entirely on access: an inline four is a 90 dollar job, while a transverse V6 needing the intake removed to reach the rear bank easily triples it. Diagnosis typically runs 100 to 200 dollars, and a compression or leak-down test adds 100 to 200 more. If a melted catalytic converter is found after prolonged misfire, add 800 to 2500 dollars.
- Replacing the coil because it is easy, then repeating the job when the misfire stays. Swap it to another cylinder first; the answer is free.
- Replacing only one spark plug. Plugs wear as a set and a mismatched new plug hides the pattern the old ones would have shown.
- Guessing which physical cylinder is number 2. Confirm the numbering for the specific engine before touching anything.
- Reading a single-cylinder code as proof that no shared cause is possible. Marginal fuel pressure or a central vacuum leak shows up on the weakest cylinder first, which is why the counters on every cylinder get read before the diagnosis narrows.
- Overlooking oil in the spark plug tube from a leaking valve cover gasket, which kills coils repeatedly until the leak is fixed.
- Ignoring a flashing MIL and driving home anyway. That drive is what turns a coil bill into a catalytic converter bill.
- Forgetting the ECM coil driver circuit. If a new coil and a new plug both fail to fix it, test the wiring and trigger signal before buying anything else.
- Assuming a lean or rich fuel trim reading caused the misfire when the misfire itself is skewing the oxygen sensor readings.
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Reviewed
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