How to Diagnose and Fix a Misfire in Your 2020 Honda Fit

How to Fix Misfire

A misfire in your 2020 Honda Fit is a serious issue that can lead to poor performance, increased emissions, and potential damage to the catalytic converter. It occurs when the air-fuel mixture in one or more cylinders fails to ignite properly. Based on analysis of owner discussions, a common theme points to foundational issues with the vehicle's core systems, often described as problems with the "baselayer" or fundamental components. As one owner shared regarding a different repair, the need to modify or address core mounting points is critical: "Note: if you have a FMIC that uses a top center mount and choose to get this set. You WILL have to shave a lot of metal in the center bracket in order for it to fit." This highlights how improper fitment or failure of primary components can cascade into operational problems.

Symptoms

Owners report a variety of symptoms that signal a misfire, often starting subtly before becoming more severe. The most common indicator is a rough running engine, where you'll feel pronounced shaking or vibration, especially at idle or under light acceleration. This roughness is the direct result of one cylinder not firing, forcing the engine to run unevenly on the remaining cylinders.

Another frequent symptom is a noticeable loss of power and hesitation during acceleration. The vehicle may feel sluggish, struggle to maintain speed on inclines, or jerk when you press the gas pedal. This happens because the engine's computer (ECM) is trying to compensate for the misfiring cylinder by adjusting timing and fuel trim, but it cannot fully make up for the lost power. You might also observe a change in the exhaust note, which can become lumpy or produce a sputtering sound.

The most definitive warning will come from your dashboard. The check engine light will illuminate, and it will often flash during active, severe misfires that can damage the catalytic converter. Using a basic OBD2 scanner, you will likely retrieve codes such as P0300 (random misfire), P0301, P0302, P0303, or P0304, which correspond to a specific cylinder. In some cases, owners have noted related issues like a "knock" or "loose connection," which can be both a symptom and a cause of the erratic combustion event.

Most Likely Cause

The primary cause of misfires in the 2020 Honda Fit, as indicated by owner discussions, is a failure in the vehicle's foundational systems—the "baselayer." This is not a single part but refers to the integrity of core engine components and their connections that are essential for proper combustion. For the L15B 1.5L engine in this model, this often manifests as issues with ignition components (coils, spark plugs), fuel delivery (injectors), or mechanical compression (valves, piston rings).

A critical aspect of this baselayer failure is environmental degradation, specifically corrosion. Owners in regions that use road salt have expressed significant concern about component longevity. As one owner succinctly put it regarding underbody protection: "Really would like to avoid paying $200 if I can, but also don’t want salt destroying everything underneath in winter." This corrosion can attack electrical connections to ignition coils and fuel injectors, creating high-resistance or intermittent "loose connections" that disrupt the critical signals needed for firing. Corrosion can also affect grounding points, sensor connectors, and even the physical components themselves, leading to the "sick" running condition described by owners.

How to Diagnose

Diagnosing a misfire requires a methodical approach to isolate the failed component within the "baselayer." You will need an OBD2 scanner, a basic set of hand tools (sockets, ratchet, extension), and possibly a multimeter for checking electrical continuity.

First, connect your OBD2 scanner to the port under the dashboard. Read the stored codes. A specific cylinder code (e.g., P0301 for cylinder 1) gives you a direct starting point. If the code is P0300 (random/multiple misfire), the cause could be more systemic, like a vacuum leak, low fuel pressure, or a faulty crankshaft position sensor. Record the freeze frame data, which shows engine conditions (RPM, load, temperature) when the code was set.

Next, perform a visual inspection. With the engine off, inspect the ignition system. Look for any obvious damage to the wiring harness leading to the coils and injectors. Check for corrosion on electrical connectors, a key concern from owner data. Look for cracked or damaged coil pack boots and listen for any audible vacuum leaks (a hissing sound) around the intake manifold and vacuum hoses.

For a specific cylinder code, the simplest test is a component swap. Swap the ignition coil from the misfiring cylinder with one from a known good cylinder. Clear the codes, drive the vehicle, and see if the misfire code follows the coil. If it does, you've found the faulty coil. If not, repeat the process with the spark plug. If the code remains on the original cylinder after swapping both coil and plug, the issue likely lies with the fuel injector, a compression problem (worn valves, rings), or a wiring fault to that specific cylinder.

Step-by-Step Fix

Once you've diagnosed the faulty component, follow these steps to repair the misfire. This guide assumes you have identified a faulty ignition coil as the culprit, a common point of failure.

1. Safety First: Ensure the vehicle is parked on a level surface, the parking brake is engaged, and the engine is completely cool. Disconnect the negative terminal of the 12-volt battery to prevent any electrical shorts or accidental engine starts.

2. Locate and Access: Open the hood and locate the ignition coils. They are mounted directly on top of the valve cover, each with a single electrical connector. You may need to remove a plastic engine cover, which typically snaps off or is held by a few bolts.

3. Disconnect the Electrical Connector: Press down on the locking tab of the electrical connector on the faulty coil and pull it straight off. Be gentle but firm.

4. Remove the Coil Pack Bolt: Each coil is secured by a single 10mm bolt. Use a socket with an extension to remove this bolt. Set it aside in a safe place.

5. Remove the Faulty Coil: Firmly grasp the coil pack and pull it straight up and out of its spark plug well. It may require a bit of wiggling if it's seated tightly. Inspect the rubber boot for any tears, cracking, or signs of carbon tracking (black lines), which indicate failure.

6. Inspect the Spark Plug (Recommended): While the coil is out, it is highly advisable to remove and inspect the corresponding spark plug. Use a spark plug socket and extension to unscrew it. Check the electrode for excessive wear, oil fouling, or abnormal deposits. This is a key part of maintaining the "baselayer." As one owner's experience with modifications suggests, ensuring proper fitment is paramount: "You WILL have to shave a lot of metal in the center bracket in order for it to fit." While not about a spark plug, the principle of correct installation is universal.

7. Install New Components: If replacing the spark plug, apply a small amount of anti-seize compound to the threads (if not pre-applied) and thread it in by hand to avoid cross-threading. Torque it to specification (typically 13-20 ft-lbs for this engine). Before installing the new coil, apply a thin layer of dielectric grease inside the rubber boot. This improves the seal and prevents moisture intrusion, combating the corrosion issue owners fear. Push the new coil pack down firmly over the spark plug until it is fully seated.

8. Reassemble: Reinstall the 10mm mounting bolt and tighten it securely. Reconnect the electrical connector until it clicks into place.

9. Repeat if Necessary: If you are replacing multiple coils or plugs, repeat the process for each cylinder.

10. Final Steps: Reconnect the negative battery terminal. Start the engine and let it idle. It may run roughly for a few seconds as the ECM relearns fuel trims. Use your OBD2 scanner to clear the diagnostic trouble codes. Take the vehicle for a test drive, ensuring the check engine light remains off and the engine runs smoothly under acceleration.

Parts and Tools Needed

• Ignition Coil: Use OEM or high-quality aftermarket equivalents. An example part number is 30520-5B9-A01 (coil assembly, but confirm for your specific VIN).
• Spark Plugs: OEM recommended are NGK or Denso Iridium. Part number DILKAR7B11G (NGK) or equivalent. Always replace in a full set of 4.
• Dielectric Grease: A small tube for coating coil boots and electrical connectors to prevent corrosion.
• Anti-Seize Compound: For spark plug threads (often not needed if plugs have coated threads).
• Basic Hand Tools: 10mm socket, ratchet, 3-6 inch extension, spark plug socket (5/8" or 16mm).
• OBD2 Scanner: Essential for reading and clearing codes.
• Torque Wrench: Recommended for proper spark plug installation.

Real Owner Costs

The cost to fix a misfire varies dramatically between DIY and professional repair, largely dependent on the root cause.

DIY Repair (Ignition Coil & Spark Plugs):

• Parts: A single OEM ignition coil can cost $60-$90. A set of 4 high-quality iridium spark plugs is about $40-$60. A tube of dielectric grease is under $10.
• Tools: If you need to purchase an OBD2 scanner and basic socket set, an initial investment of $100-$150 is possible, but these tools are reusable.
• Total DIY Cost (for one coil and plugs): Approximately $110 - $160 for parts only, assuming you have tools.

Professional Repair: Shop rates add significant cost. Diagnosis typically incurs a 1-hour labor charge ($100-$150). Replacing one coil and a set of spark plugs may be billed as 1-1.5 hours of labor.

• Dealership (One Coil + Plugs): Parts marked up 30-50%, plus 1.5 hours labor. Total often $400 - $600.
• Independent Shop: Lower parts markup and labor rate. Total often $250 - $400.

The cost escalates if the issue is a fuel injector ($150-$300 per injector plus several hours labor) or a mechanical problem like low compression, which requires a leak-down test and potentially a major engine repair costing thousands. The owner concern about a $200 part for a splash guard underscores the value perception: "Really would like to avoid paying $200 if I can..." Applying that mindset here, a DIY coil replacement offers substantial savings.

Prevention

Preventing misfires centers on proactive maintenance and protecting your vehicle's "baselayer" from environmental and wear factors.

1. Adhere to Severe Service Schedules: If you drive in extreme conditions—frequent short trips, stop-and-go traffic, or in cold, salty climates—consider changing spark plugs more frequently than the recommended 100,000-mile interval. Inspect them every 60,000 miles.
2. Combat Corrosion: Regularly inspect engine bay electrical connections, especially in winter. After driving on salted roads, rinse the undercarriage and engine bay (when cool) periodically. Applying dielectric grease to ignition coil and sensor connectors during services creates a protective barrier.
3. Use Quality Fuel and Additives: Consistently use Top Tier detergent gasoline to keep fuel injectors clean. A periodic fuel system cleaner can help prevent injector clogging.
4. Address Issues Immediately: Do not ignore a flashing check engine light. Driving with a severe misfire can dump unburned fuel into the exhaust, overheating and destroying the catalytic converter—a repair that can cost over $1,000.
5. Regular Tune-Ups: Follow the factory maintenance minder system strictly. This includes timely air filter changes to ensure proper airflow and engine breathing.

What Owners Say

Real experiences from HONDA owners:

Owner Experiences

"Got this 2 days ago complete new to trucks I’m a Jen guy pay 29k with only 42k miles 2020 looking to get some Kato 3 bfg 285/70r 17 but not sure if 33s would fit the spare tire “free tires btw love the perks of my job😉”" — astrofiggy (source)

"Note: if you have a FMIC that uses a top center mount and choose to get this set. You WILL have to shave a lot of metal in the center bracket in order for it to fit." — AceCubesMcfrost (source)

"Factory Rubicon suspension on unlimited sport? There's a local guy selling a set of Rubicon fox shocks control arms and springs from a 2020 Rubicon JT and claims they only have 2000 miles on them." — djdb05 (2,000 miles) (source)

Real Repair Costs

"Or maybe a universal fit that works? Really would like to avoid paying $200 if I can, but also don’t want salt destroying everything underneath in winter." — Dry_Preference1208 (source)

"Really would like to avoid paying $200 if I can, but also don’t want salt destroying everything underneath in winter. Any suggestions or leads would be appreciated!" — Dry_Preference1208 (source)

"Had my $125 Amazon one since 2020, and it's flawless except for where I broke it pushing stuff in that didn't fit. Good news is they're still $125, so if it ever quits latching I'll replace it for cheap." — asbestoswasframed (source)

FAQ

Q: How long does it take to fix a misfire caused by an ignition coil? A: For a competent DIYer, diagnosing which cylinder is misfiring and replacing a single coil and its spark plug typically takes 30 to 60 minutes. If replacing all four coils and plugs, plan for 1.5 to 2 hours. A professional shop will usually complete the job within an hour of labor time once diagnosed.

Q: Can I drive my 2020 Honda Fit with a misfire? A: It depends on the severity. If the check engine light is solid, the misfire is minor or intermittent. You can drive cautiously for a short distance to a repair shop, but address it promptly. If the check engine light is flashing, this indicates a severe misfire that can cause immediate damage to the catalytic converter. You should stop driving as soon as safely possible and have the vehicle towed.

Q: Is this a common issue on the 2020 Honda Fit? A: While the L15B engine is generally reliable, ignition coil failures are a common wear item across many modern direct-injection engines, including this one. Environmental factors like heat and moisture (leading to corrosion) are significant contributors. Issues related to the foundational "baselayer" components like coils and plugs are among the most frequent causes of drivability complaints for this model year.

Q: DIY vs mechanic - what's recommended for a misfire? A: If you are comfortable with basic hand tools and can follow the diagnostic steps (especially using an OBD2 scanner), replacing ignition coils and spark plugs is a very accessible DIY job. The cost savings are substantial. However, if the diagnosis points to a fuel injector, internal engine problem (low compression), or persistent electrical fault, the complexity increases significantly. In those cases, the specialized tools and expertise of a professional mechanic are strongly recommended. The DIY approach is best for the most common, straightforward causes.

Q: Will a misfire cause my vehicle to fail an emissions test? A: Absolutely. A misfire increases hydrocarbon (HC) emissions dramatically because unburned fuel is exiting the cylinder. Your vehicle will not pass a tailpipe emissions test or an OBD2 system check (since the check engine light will be on and monitors will not be ready).

Q: Can bad gas cause a misfire? A: Yes, contaminated or low-octane fuel can cause pre-ignition (knock) and misfires. The engine's knock sensor will try to compensate by retarding timing, which can lead to rough running. This is usually a temporary condition. Adding a bottle of fuel system cleaner and filling up with high-quality Top Tier gas from a reputable station can often resolve it. If the misfire persists after a tank of good fuel, the cause is likely mechanical or electrical.