Engine misfires w/ code P0302. Spark plug or ignition coil pack? Diagnosis and fix. 

Check engine light P0302. Spark plug or ignition coil pack? Diagnosis and fix.
Or related code P0301, P0303, P0304, P0305, P0306, P0307, P0308.
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Vehicle: 2010 Honda Odyssey Ex-L
Engine: Honda V6 J35A7
Problem
Code: P0302 Cylinder 2 Misfire
Analysis
Most common causes:
1. Spark plug; OR
2. Ignition coil pack;
Test
1. Take out the ignition coil pack from a GOOD cylinder, e.g. cylinder 4.
2. Take out the ignition coil pack from the BAD cylinder, i.e. cylinder 2.
3. Swap the two coil pack, that is:
* Install coil pack \#2 to cylinder 4
* Install coil pack \#4 to cylinder 2
4. Clear code, start the engine, and scan engine.
Result and Fix
Scenario 1
IF the code changed to:
"P0304 cylinder 4 misfires"
meaning the GOOD cylinder is now bad with the new coil pack, replace the coil pack.
Scenario 2
IF the code comes back with an unchanged misfire code:
"P0302 cylinder 2 misfires"
Then the coil is not the culprit, and it is most likely the spark plug in the BAD cylinder. Replace the spark plug:
1. With a spark plug socket, take out the old plug from the BAD cylinder, i.e. number 2.
2. Thread the new plug on with a small ratchet and fingers.
3. Torque to 13 ft-lb, or hand-tight.
* No grease (anti-seize)
* Do NOT over-tighten
4. Clear the code and have a test drive.
5. All done if code doesn't come back.
Notes
On spark plug replacement:
1. If it has been a while since last spark plug replacement, you may consider replace them ALL.
2. If one starts to go out, it's likely the others will do too.
3. Don't stretch it as it can lead to more costly repairs later.
4. Examples on spark plug replacement intervals:
* Honda engines: no more than 100k miles
* Toyota engines (old): no more than 120k miles
* Toyota engines (latest): no more than 60k miles
On other causes of misfire:
1. Bad fuel
2. Bad fuel injection
3. Engine lubrication, oil getting into combustion
4. Others
Fix the problem ASAP as it can lead to more catastrophic problems on the engine and/or catalytic convertor, which are very costly.
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