What Is Code P0302 on a 2004 Honda Civic?

P0302 on a 2004 Honda Civic means “Cylinder 2 Misfire Detected.” In plain terms, the engine control module has identified that the second cylinder isn’t firing reliably. This can cause rough running, reduced power, and potentially a flashing check-engine light if the misfire is severe. Because prolonged misfires can damage the catalytic converter, it’s best to diagnose and fix the issue promptly.

What the Code Means

P0302 is a generic OBD-II fault code indicating the engine detected irregular combustion in cylinder 2. The code does not specify the root cause; it only tells you which cylinder is misfiring. On a 2004 Civic—whether the common 1.7L D17 engine (DX/LX/EX) or the 2.0L K-series in the Si—the diagnostic approach is similar.

How Cylinder Numbering Works on This Civic

On Honda inline-four engines in this generation, cylinder 1 is located at the end of the engine nearest the timing belt/chain (passenger side on U.S. models), followed by cylinders 2, 3, and 4 toward the transmission. Cylinder 2 is the second from the passenger side. If you’re checking coils or plugs, the second coil from the passenger side serves cylinder 2.

What You Might Notice

Drivers commonly experience several drivability symptoms when cylinder 2 is misfiring. These can range from mild roughness to severe hesitation and warning lights.

• Rough idle, shaking, or vibration—especially at stops
• Hesitation, stumbling, or lack of power under acceleration
• Poor fuel economy and increased emissions
• Check-engine light on; flashing MIL if the misfire is severe
• Possible fuel smell in exhaust or sulfur/rotten-egg odor from converter stress
• Hard starts or stalling in more serious cases

If the check-engine light flashes, it signals a catalyst-damaging misfire; reduce load and address the issue immediately.

Common Causes on a 2004 Civic

Misfires come down to problems with spark, fuel, air/vacuum, or engine compression/timing. On seventh-generation Civics, several patterns are well known to technicians.

• Ignition faults: worn or fouled spark plug, failing coil-on-plug for cylinder 2, damaged coil connector or wiring, oil intrusion in the spark plug tube from a valve cover gasket leak.
• Fuel delivery: clogged or weak injector on cylinder 2, wiring/connectors to the injector, low fuel pressure (pump, filter, regulator issues).
• Air/vacuum issues: intake manifold gasket air leak (especially in cold weather on some models), cracked or disconnected vacuum hoses, PCV system leaks.
• Sensor and control inputs: faulty MAF/MAP readings (contamination or failure), engine coolant temperature sensor issues affecting warm-up fueling, or less commonly, ECM faults.
• Engine mechanical: low compression from worn rings, burnt valve(s), valve lash out of spec, head gasket leak, or timing belt stretch/jump (1.7L uses a timing belt; K-series Si uses a timing chain).
• EGR-related issues (if equipped): sticking EGR valve or clogged passages can contribute to misfires at cruise.

Not all causes apply to every trim, and multiple factors can overlap. Start with the most likely: spark plugs and coils, then move to injector and air leaks, and finally mechanical checks.

How to Diagnose Step-by-Step

A methodical approach saves time and money. Basic tools (OBD-II scanner, spark plug socket, multimeter) and a few simple tests can quickly isolate the fault.

1. Confirm the code: scan for P0302 and note freeze-frame data (RPM, load, temperature). Look for related codes like P0300 (random misfire), P0171 (system too lean), or fuel/ignition codes that narrow the path.
2. Visual inspection: check the cylinder 2 coil connector and harness for corrosion or broken wires. Remove the coil and inspect the spark plug well for oil or coolant. Oil in the well points to a valve cover/tube seal leak.
3. Spark plug check: remove the cylinder 2 plug. If it’s worn, fouled, cracked, or incorrectly gapped (spec is about 1.0–1.1 mm/0.039–0.044 in), replace with the correct NGK/Denso iridium plugs. Do not bend the iridium center electrode; plugs come pre-gapped.
4. Coil swap test: swap the cylinder 2 coil with another cylinder (e.g., cylinder 3). Clear codes and test drive. If the misfire follows the coil (now shows P0303), the coil is faulty.
5. Injector test: listen for injector click on cylinder 2, check for power and ground with a noid light, and consider swapping injectors between cylinders. If the misfire follows the injector, clean or replace it.
6. Vacuum/air leaks: spray around the intake manifold gasket and vacuum lines while monitoring fuel trims/idle speed; changes suggest a leak. Cold-weather intake gasket leaks were a known issue on some seventh-gen Civics.
7. Fuel system check: verify fuel pressure and volume if multiple cylinders show lean symptoms or if P0171 accompanies the misfire.
8. Mechanical integrity: run a compression test and, if needed, a leak-down test. Low numbers on cylinder 2 compared with others point to valve or ring issues; listen for air at the intake (intake valve), exhaust (exhaust valve), or crankcase (rings).
9. Timing verification: on the 1.7L, ensure the timing belt hasn’t jumped a tooth if misfires occur after belt service or at high mileage.
10. Final verification: after repairs, clear codes and perform a thorough road test across varying loads to confirm the fix.

Working from simple to complex helps prevent unnecessary parts replacement. If results are inconclusive, mechanical and timing checks are essential before moving on.

Recommended Fixes and Typical Costs

Once the root cause is found, targeted repairs usually resolve P0302 without replacing major components.

• Spark plugs: replace the full set with OEM-spec iridium plugs; parts typically $40–$80 for four. Torque to spec per the service manual (about 13 lb-ft for many Honda M14 plugs).
• Ignition coil (cyl 2): $50–$120 each for quality OEM or OEM-equivalent; easy DIY on coil-on-plug systems.
• Valve cover/tube seals: gasket set $20–$50; fixes oil in plug wells that causes misfires.
• Fuel injector service: professional cleaning $80–$150; replacement injector $80–$200 plus seals.
• Intake manifold gasket: upgraded gasket $20–$40; labor 1–2 hours; addresses cold-start lean/misfire from air leaks.
• Fuel system: filter (if serviceable) and pressure-related fixes vary; pump/module can be $200–$500 parts.
• Valve clearance adjustment: can improve idle quality and reduce risk of burnt valves; labor varies ($100–$300+). A burnt valve or head work can exceed $1,000–$1,800.
• Timing belt (1.7L): if out of time or overdue, a full belt service (belt, tensioner, water pump) is prudent; $400–$900 depending on region and parts.

Choose quality parts (NGK/Denso plugs, reputable coils/injectors) and confirm the fault before purchasing. Clearing codes without addressing the cause will typically see the misfire return.

Can You Keep Driving?

If the check-engine light is steady and the car drives acceptably, short trips to a shop are usually fine. If the light flashes, reduce load immediately and avoid driving—raw fuel can overheat and destroy the catalytic converter quickly. Persistent misfires also risk engine damage over time.

Preventive Tips

Regular maintenance reduces the likelihood of misfires and can catch small issues before they become costly repairs.

• Replace spark plugs at the recommended interval with OEM-spec iridium parts.
• Inspect coils and plug wells for oil during routine services; fix valve cover leaks promptly.
• Check and maintain proper valve clearance at the intervals recommended in your service schedule.
• Address vacuum leaks and cracked hoses; consider the updated intake manifold gasket if you experience cold-weather lean/misfire symptoms.
• Use quality fuel and keep the air filter and PCV system in good condition.

Proactive care helps maintain smooth operation and protects the catalytic converter and engine internals.

FAQs

Where exactly is cylinder 2 on my 2004 Civic?

Facing the engine from the front of the car, cylinder 1 is at the passenger side (timing belt/chain end), then 2, 3, and 4 toward the driver’s side. Cylinder 2 is the second from the passenger side.

Do I need to replace all four ignition coils?

Not necessarily. Use swap testing to confirm a single bad coil. If mileage is very high and multiple coils are weak, replacing the set can be preventive, but it’s not mandatory if only one is faulty.

Summary

P0302 on a 2004 Honda Civic indicates a misfire on cylinder 2. Most fixes involve the ignition system (plug/coil), fuel injector issues, vacuum leaks (notably intake gasket on some models), or, less commonly, mechanical problems like valve or timing faults. Diagnose systematically—scan data, inspect and swap-test components, check for air/fuel issues, then verify compression. Repair promptly, especially if the MIL flashes, to avoid catalytic converter damage and restore smooth, efficient operation.

How do I fix error code P0302?

To fix the P0302 error code (cylinder 2 misfire), you should first inspect and replace the spark plug in cylinder 2, then check the ignition coil by swapping it with a known good one from another cylinder to see if the misfire code follows. If the problem shifts, the coil is bad and needs replacement. If the problem remains, inspect the fuel injector and check for vacuum leaks, fuel pressure issues, or mechanical problems in cylinder 2. 
1. Check the Spark Plug 

• Inspect the spark plug: Remove the spark plug from cylinder 2 and inspect it for fouling (covered in fuel or oil) or wear. 
• Replace it: If the spark plug looks bad, replace it with a new one. Worn-out or fouled spark plugs are a common and inexpensive fix. 

This video demonstrates how to inspect and replace a spark plug for cylinder 2: 59sProfessor’s GarageYouTube · Feb 12, 2023
2. Check the Ignition Coil 

• Swap the coil: If the spark plug looks fine, remove the ignition coil from cylinder 2 and swap it with the coil from a different cylinder (e.g., cylinder 3). 
• Scan for the code again: Clear the P0302 code and start the engine. 
• Diagnose: If the misfire code changes to the cylinder you swapped with (e.g., P0303), the ignition coil is faulty and needs to be replaced. 

This video explains how to swap ignition coils to diagnose a misfire code: 56sFIXDYouTube · Mar 13, 2019
3. Check the Fuel System 

• Inspect the fuel injector: If the issue doesn’t follow the coil, the fuel injector for cylinder 2 may be faulty. You can try cleaning the injector or, if possible, swap it with a good one to see if the misfire follows. 
• Check fuel pressure: Ensure the fuel system has adequate pressure and volume. 

4. Address Other Potential Issues

• Check for vacuum leaks: . Opens in new tabInspect the intake manifold for any vacuum leaks that could be affecting the fuel mixture in cylinder 2. 
• Check for mechanical issues: . Opens in new tabProblems with internal engine components, such as leaking head gaskets or damaged valves, can cause misfires and require more extensive repairs. 

This video covers other potential issues, such as vacuum leaks and mechanical problems: 53sDaniel’s Car Talk ChannelYouTube · Aug 11, 2024
When to See a Professional 

• If you’ve tried these steps and the P0302 code persists, or if you’re uncomfortable with any of the diagnostic procedures, it’s best to take your vehicle to a professional mechanic. They can perform more in-depth diagnostics to identify and fix the root cause of the misfire.

How to fix misfire in cylinder 2?

To fix a cylinder 2 misfire, check and replace the spark plug, swap the ignition coil or spark plug wire to see if the misfire moves to another cylinder, and then inspect or swap the fuel injector if the ignition system components are ruled out. If the misfire persists, consider checking for vacuum leaks or performing a compression test to rule out internal engine issues, such as faulty valves or piston rings. 
1. Check the Spark System 

• Inspect the Spark Plug: . Opens in new tabRemove the spark plug from cylinder 2 and examine it for fouling, damage, or excessive wear. If it looks bad, replace it. 
• Test the Ignition Coil: . Opens in new tabSwap the ignition coil from cylinder 2 with one from a known good cylinder. If the misfire code changes to the other cylinder, the coil is faulty and needs to be replaced. 
• Inspect Spark Plug Wires: . Opens in new tabCheck the spark plug wire for damage, such as cracks or fraying. Swapping the wire with a known good one is another way to diagnose a problem. 

This video shows how to test a spark plug and swap it with a known good one to diagnose the issue: 59sProfessor’s GarageYouTube · Feb 12, 2023
2. Check the Fuel System 

• Inspect the Fuel Injector: Test the fuel injector by swapping it with one from a known good cylinder. If the misfire moves to the other cylinder, the injector is faulty and should be replaced.

3. Check for Air/Vacuum Leaks 

• Inspect the Intake Manifold: Look for any cracks or damaged gaskets on the intake manifold that could cause a vacuum leak.

4. Perform a Compression Test 

• Test Cylinder Compression: If the spark and fuel systems are in good order, a misfire can be caused by internal engine problems like faulty piston rings or valves. A compression test can help determine if there is a mechanical issue.

5. Seek Professional Help 

• Consult a Mechanic: If you’ve followed these steps and the misfire persists, it’s time to take your vehicle to a qualified mechanic for further diagnosis and repair.

What is the most common cause of a P0302 code?

The most common cause of a P0302 code (Cylinder 2 Misfire Detected) is a faulty spark plug or ignition coil in cylinder 2. Other potential causes include a faulty fuel injector, issues with cylinder compression, or problems with the wiring and connections related to the ignition or fuel system. 
Here’s a more detailed breakdown:
Common Causes:

• Faulty Spark Plug: . Opens in new tabWorn or damaged spark plugs in cylinder 2 are a frequent culprit. 
• Faulty Ignition Coil: . Opens in new tabThe ignition coil provides the spark, and a malfunctioning coil for cylinder 2 can lead to misfires. 
• Fuel Injector Issues: . Opens in new tabA clogged or malfunctioning fuel injector in cylinder 2 can disrupt the fuel delivery, causing a misfire. 
• Cylinder Compression Problems: . Opens in new tabProblems like worn valves, piston rings, or a leaking head gasket can affect cylinder compression and cause misfires. 
• Wiring and Connections: . Opens in new tabDamaged or corroded wiring or connectors in the ignition or fuel system for cylinder 2 can disrupt the signal flow. 

Troubleshooting Steps:

1. Check the spark plugs and ignition coils: Inspect and replace them if necessary, or swap them with another cylinder to see if the misfire follows. 
2. Inspect the fuel injectors: Ensure they are clean and functioning properly. Consider using a fuel injector cleaner. 
3. Check for vacuum leaks: Inspect hoses and connections around cylinder 2 for any leaks. 
4. Check cylinder compression: This may require specialized tools and knowledge. 
5. Check for wiring issues: Inspect wiring harnesses and connectors related to cylinder 2’s ignition and fuel systems. 

Important Considerations:

• Misfire Detection: The Powertrain Control Module (PCM) detects misfires by monitoring the crankshaft speed. When a cylinder misfires, the PCM registers a loss of RPM and can trigger the P0302 code. 
• Other Codes: If other codes are present, they might be related to the misfire and should be addressed as well. 
• Professional Diagnosis: If the issue persists after basic troubleshooting, it’s recommended to seek professional help from a qualified mechanic. 

What is the most common reason for cylinder 2 misfire?

The majority of the time, a misfire is caused by a faulty spark plug or another problem with the spark system, but it may also be due to: A fuel delivery problem. A mechanical engine failure. Exhaust gas recirculating.