OBD-II code guide
P0302 – Cylinder 2 Misfire
P0302 means cylinder 2 isn’t contributing cleanly. Unlike P0300, you can swap parts between cylinders and watch the code follow the failed piece.
Running P0302 on a real vehicle? Torqmind AI Mechanic locks onto your year/make/model and walks the next test — not a generic forum thread.
Ask MasterMind about P0302What P0302 really means
Single-cylinder misfire codes are a gift: the computer already told you which hole is weak. The disciplined path is spark → fuel → mechanical. Most P0302 jobs end at a coil or plug — but only after you prove it with a swap, not a receipt for a full ignition kit you didn’t need.
The ECM tracks crank acceleration per cylinder event. When cylinder 2’s contribution drops, misfire counters for #2 climb and P0302 sets. Freeze-frame tells you whether it happened at idle, cruise, or heavy load — heat-soak coil failures often show up only when hot.
Common symptoms
- Rough running that may worsen under load or when hot
- Check engine light with P0302 (sometimes pending first)
- Vibration at idle that smooths slightly if you unplug that coil (for test only)
- Stumble on tip-in or highway pull
Most likely causes (ranked thinking)
1. Ignition coil on cylinder 2
Most common on coil-on-plug engines. Heat and age crack the boot or weaken the coil. Swap proves it.
2. Spark plug on cylinder 2
Worn, cracked, oil-fouled, or wrong-gap plug. Always read the plug when the coil comes off.
3. Fuel injector on cylinder 2
Clogged, stuck, or electrically open. Less common than spark — prove after coil/plug.
4. Wiring or connector
Oil intrusion, broken locks, or chafe near the valve cover. Wiggle tests catch intermittents.
5. Compression / mechanical
Valve, ring, or head issues. Last after spark and fuel are proven good on that cylinder.
How to diagnose P0302
Work top to bottom. Don’t skip to the expensive part until the cheap tests point there.
Step 1: Save codes and note conditions
Cold-only, hot-only, or under load changes what you chase first.
Step 2: Swap the #2 coil with a neighbor
Clear or watch misfire counters. If P0302 becomes P030x on the other hole, replace that coil.
Step 3: Inspect the #2 spark plug
Look for oil, fuel wash, cracked porcelain, or wrong gap. Replace if questionable.
Step 4: Check the connector and harness
Corrosion, pushed pins, and oil in the connector are common intermittent causes.
Step 5: Move to injector / compression only if spark is proven
Contribution test, swap injector if practical, then compression or leak-down.
What not to do
- Don’t buy a full coil set until the fault follows a swap.
- Don’t skip reading the plug — it tells you oil vs fuel vs normal wear.
- Don’t jump to a head gasket story before spark and fuel are clean.
When it gets serious
A hard miss under load can overheat the catalytic converter. If the light flashes, back off. If you find coolant or heavy oil fouling on #2, stop guessing and measure compression.
After the repair
Confirm the code is gone and misfire counters for cylinder 2 stay quiet on a hot road test. If a different cylinder code appears, repeat the swap path there — don’t assume the first coil fixed “everything.”
FAQ
Should I replace all coils for a P0302?
Not first. Swap the coil and let the code tell you. Replace the failed part, then decide on the rest based on mileage and condition.
P0302 only when warm — what then?
Heat-related coil or connector faults are common. Still prove with a hot swap before buying a full set.
Can a bad plug wire set P0302?
On engines that still use wires, yes. On coil-on-plug, focus on the coil boot and plug for that cylinder.
What if the code doesn’t move after a coil swap?
Then it’s less likely the coil. Read the plug, check wiring, then injector and compression in that order.
Continue in the AI assistant
Save your vehicle in MasterMind, type P0302, and get a bay-side path: top causes, next three checks, then tap what you found.
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