P0304 Code: Toyota Tacoma (2016-2023) - Causes, Symptoms & Fixes

2016-2023 Toyota Tacoma P0304 Diagnostic Guide

Important data context from NHTSA-style data provided:

• Owner complaints for this exact make/model/year/issue: No NHTSA complaints found.
• Official recalls for this exact make/model/year: No recalls found in NHTSA database.
• No recalls found in NHTSA database (stated wording as required).
• These data limitations mean follow standard diagnostics and common-car knowledge unless a recall/TSB emerges in the dataset.

CODE MEANING AND SEVERITY

• What P0304 means

  • P0304 is an OBD-II diagnostic trouble code indicating a cylinder 4 misfire. The engine control module (ECM) detected that cylinder 4 is not combusting the air-fuel mixture properly. The misfire can happen at idle, during acceleration, or under load, and it often triggers the Check Engine Light (CEL).

• Severity considerations

  • A cylinder misfire can be benign momentarily, but repeated misfires can cause engine damage, excessive catalyst heating, and elevated emissions. A persistent misfire (especially with a flashing CEL) is a sign you should address the issue promptly to avoid downstream damage or failed emissions tests.

COMMON CAUSES ON TOYOTA TACOMA (2016-2023)

• Most frequent culprits
  • Worn or fouled spark plug in cylinder 4
  • Bad ignition coil on cylinder 4 (coil-on-plug type common on modern Tacomas)
  • Faulty or sticking fuel injector on cylinder 4
  • Vacuum leak or intake manifold runner issue around cylinder 4
  • Low compression in cylinder 4 (valve, piston rings, or head-gasket concerns)
  • Dirty/ingested air or fuel mixture issues (e.g., MAF/MAP sensor or intake air leaks can contribute to misfire perception)
  • Dirty or leaking PCV system or hoses adjacent to cylinder 4
  • In rare cases, wiring/connectors for the ignition coil or injector on cylinder 4 can be loose or corroded
• Why cylinder 4 is often the starting point
  • With coil-on-plug designs, one weak ignition coil or fouled plug tends to be the most straightforward, observable fix. If misfire does not follow a suspect part after swapping, move to fuel or mechanical causes.

SYMPTOMS YOU MIGHT NOTICE

• Engine behavior
  • Rough idle or vibration when the engine is cold or warm
  • Intermittent or consistent loss of power on cylinder 4, especially under load or acceleration
  • Harsh throttle response or hesitation
  • Reduced fuel economy
  • Engine runs rough enough that you feel it through the seat or steering wheel
• Exhaust and emissions
  • Check Engine Light illuminated (solid) or flashing depending on severity
  • Possible catalytic converter heat/overheat if raw fuel reaches the exhaust
• Other symptoms
  • No obvious external leaks or drips, but plug/coil failure may show as code P0304 or P0300 if the misfire is severe or persistent

DIAGNOSTIC STEPS (SYSTEMATIC, START TO FINISH)

Warning: Start with a proper scan, then follow a logical test plan to confirm the root cause. If you lack tools or experience, seek professional help early.

Step 1. Confirm the DTC and capture data

• Use a scan tool to confirm P0304 and check related data:
  • Freeze frame data (RPM, load, coolant temp)
  • Misfire counters per cylinder (live misfire data, if available)
  • Other DTCs (P0300, P0316, P0350-P0354, P0171/P0174, etc.) that can influence misfire interpretation
• Note whether the misfire is intermittent (often idle-only) or steady during driving.

Step 2. Visual inspection

• Inspect cylinder 4 spark plug:
  • Look for wear, fouling (oil, fuel, carbon), or damage
  • If the spark plug is oil-fouled or heavily fouled, consider oil control ring wear or valve seal issues
• Inspect ignition coil and boot for cylinder 4:
  • Check for cracks, arcing, corrosion on the connector, or a loose boot
• Inspect nearby vacuum lines, intake ducts, and PCV hoses for cracks or leaks around cylinder 4 area
• Look for oil leaks that could foul the plug or affect coil performance

Step 3. Swap-test to isolate coil/plug vs. injector

• Coil/plug swap:
  • Swap the ignition coil (and if applicable the spark plug) from cylinder 4 with another cylinder (e.g., cylinder 1). Clear codes and run the vehicle to see if the misfire follows the coil/plug.
  • If the misfire moves to the new cylinder, the coil/plug is the likely culprit.
  • If the misfire stays on cylinder 4, suspect the injector, compression, or a mechanical issue.
• Spark plug swap:
  • If you notice a possible plug issue, temporarily moving or swapping plugs can also help isolate the problem, though coil tests are typically more decisive.

Step 4. Spark plug replacement (if worn/fouled)

• Replace cylinder 4 spark plug with the correct type for the 3.5L V6/Tacoma
• It is often wise to replace all plugs if one is fouled, depending on maintenance interval and wear patterns
• Use anti-seize and dielectric grease as recommended; torque spark plugs to the OEM specification and ensure they are seated properly to avoid cross-threading

Step 5. Ignition coil testing

• Resistance test (where spec is available):
  • Measure primary and secondary resistance of the cylinder 4 coil against specification in the service manual
  • Replace coil if readings are out of spec
• Functional test:
  • If your scan tool supports coil current or duty-cycle data, compare cylinder 4 coil current to others during misfire
  • If coil shows erratic behavior or intermittent misfire data, replace the coil

Step 6. Fuel injector testing for cylinder 4

• Resistance check of the injector in cylinder 4; compare to spec
• Listen for injector clicking with a mechanic’s stethoscope
• Use a noid light to confirm injector control signal from the PCM
• If injector is suspect but not easily replaced, consider injector cleaning or professional replacement

Step 7. Vacuum and intake assessment

• Perform a vacuum-leak test around the intake manifold runners and around cylinder 4’s intake port
• If a leak is found, repair the gasket or hose as needed

Step 8. Mechanical assessment (compression/leak-down)

• Perform a compression test on cylinder 4
  • If compression is significantly low, conduct a leak-down test to identify whether the problem is a valve, piston-ring, or head-gasket issue
  • Mechanical issues often require more extensive repair (circa thousands of dollars)

Step 9. Recheck and road test

• After replacement or repair, clear the codes
• Drive under various conditions (idle, light throttle, and moderate load) to verify the misfire is resolved
• If DTC returns, re-evaluate all tested components and consider a professional assessment

Note on related fault codes

• If P0304 persists, other misfire-related codes can appear, including P0300 (random/multiple misfires) and P0301–P0308 (misfire in other cylinders)
• Codes related to ignition or fuel systems (like P0351–P0356 for ignition coil circuits or P0171/P0174 for fuel trim) may accompany or precede a persistent P0304. Treat them as diagnostic clues, not a replacement for cylinder-specific testing.

RELATED CODES (for context)

• P0300 – Random/Multiple Cylinder Misfire
• P0301 – Cylinder 1 Misfire
• P0302 – Cylinder 2 Misfire
• P0303 – Cylinder 3 Misfire
• P0305 – Cylinder 5 Misfire
• P0306 – Cylinder 6 Misfire
• P0307 – Cylinder 7 Misfire
• P0308 – Cylinder 8 Misfire (if applicable to the engine variant)
• P0350–P0356 – Ignition Coil Primary/Secondary Circuit problems (sometimes appear when a coil is failing on a cylinder, including cylinder 4)

REPAIR OPTIONS AND COSTS (2025 PRICES)

Notes

• Prices vary by region, shop, and whether parts are OEM or aftermarket. Labor rates differ widely (roughly $100–$180/hour in many U.S. shops; higher in specialty shops or dealers). All figures are ballpark ranges in 2025 dollars and should be treated as approximations.

• Spark plugs (6 cylinders on the 3.5L V6 Tacoma typically use six plugs)

  • Parts: $4–$25 per plug depending on OEM/aftermarket
  • Total parts (all six): $24–$150
  • Labor: 1–3 hours total for plug replacement on a V6 (depending on access and whether other components must be removed)
  • Estimated total job (DIY lower end; shop higher end): $150–$600

• Ignition coil (per cylinder, cylinder 4 coil)

  • Parts: $40–$180 for a direct-fit ignition coil
  • Labor: 0.5–1.0 hour (per coil)
  • If replacing just cylinder 4 coil: approximate total $80–$350 (parts + labor)
  • If you replace all coils (preemptively), parts: $240–$1080; labor: similar across six coils, $120–$600

• Spark plugs + coil replacement (recommended when one misfire is suspected)

  • Parts: $64–$270 (6 plugs + 1 coil)
  • Labor: 1–2 hours
  • Total: roughly $150–$800 depending on whether you do it DIY or through a shop

• Fuel injector testing/replacement (cylinder 4)

  • Cleaning: $50–$150 (DIY cleaning or professional service)
  • Injector replacement: $150–$500 per injector
  • Labor: 0.5–2.0 hours (per injector replacement)
  • If replacing only cylinder 4 injector: $200–$850 total (parts + labor)

• Compression test / leak-down test

  • Tools or service: $100–$250 if performed professionally
  • If mechanical repair is required afterward, total costs can rise significantly depending on the severity

• Mechanical repair (severe issues: low compression, valve, piston rings, head gasket)

  • Typical range: $1,000–$5,000 or more depending on extent
  • This is far less common for a single-cylinder misfire and is usually a result of long-running misfire with mechanical damage

• Diagnostic labor

  • If you go to a shop for diagnosis alone, expect $80–$150+ per hour, plus diagnostic fees in some shops
  • A focused misfire diagnosis (P0304) may be a few hours of work, depending on the complexity and findings

DIY VS PROFESSIONAL

DIY considerations

• Pros:
  • Substantial cost savings if the problem is a simple plug/coil swap
  • You gain a better understanding of the ignition and fuel system
• Cons:
  • Access on the 3.5L V6 can be challenging; some plugs/coils are tucked under manifolds or under the engine cover
  • Misdiagnosis risk; replacing the wrong component may not fix the misfire, leading to additional costs and downtime
  • You’ll need basic tools (spark plug socket, torque wrench, multimeter, stethoscope or spray-test aids, etc.)

Professional considerations

• Pros:
  • Quick, diagnostic-driven approach with proper tools
  • Fault confirmation via advanced test modes (live data, compression tests, injector balance tests)
  • Reduced risk of cross-threading spark plugs or improper torque
• Cons:
  • Higher upfront cost than DIY
  • Time to schedule and service

DIY step-by-step quick-start (for spark plug and coil scenario)

• Tools and parts you’ll want: new spark plug(s) for the 3.5L V6, one ignition coil (cylinder 4), basic hand tools, ratchet and socket set, torque wrench, dielectric grease, anti-seize compound (if recommended by OEM), a magnetic pick-up for dropping parts in tight spaces if needed
• Steps:
  1. Disconnect the negative battery terminal
  2. Remove engine cover (if present) to access coil-on-plug assemblies
  3. Locate the cylinder 4 coil and its spark plug
  4. Disconnect the electrical connector from the coil
  5. Remove the coil mounting bolt and lift the coil out
  6. Remove the spark plug using the spark plug socket
  7. Inspect the plug, install the new plug with anti-seize as recommended and torque to spec
  8. Install the new ignition coil and connect the electrical connector
  9. Repeat for cylinder 4 (and consider replacing all plugs if you plan to do preventive maintenance)
  10. Reconnect battery, clear codes, and test-drive to confirm the fix
• Safety tips: work in a well-ventilated area, disconnect battery before mechanical work, avoid touching hot engine parts, ensure all tools are clean and dry

PREVENTION

• Regular maintenance alignment
  • Follow the Toyota maintenance schedule for spark plug replacement intervals (the 3.5L V6 Tacoma typically uses six spark plugs; check your owner’s manual for exact replacement interval for your build if iridium/platinum plugs are used)
  • Use the recommended spark plugs and ignition coils; avoid cheap non-OEM parts for critical coil-on-plug systems
• Fuel system care
  • Use high-quality gasoline appropriate for your region and avoid long-term neglect of fuel system
  • Periodic fuel system cleaning or injector cleaning as per manual or with professional service
• Air intake and vacuum health
  • Replace air filters on schedule; check for vacuum leaks around intake manifolds and hoses
• PCV and emissions system
  • Inspect PCV valve and hoses; replace if stiff or cracked
• Engine cleanliness and operation
  • Maintain coolant and oil levels; avoid overheating
  • Address engine misfires early to minimize catalyst damage and avoid unnecessary emissions issues
• Driving habits
  • Avoid prolonged periods of heavy idle or harsh driving that can exacerbate misfires
  • If you notice an intermittent misfire, addressing it sooner reduces risk to downstream components

Data limitations and transparency

• This guide uses general automotive knowledge and the provided dataset stating:
  • No NHTSA owner complaints for this exact combination (2016-2023 Tacoma P0304)
  • No recalls found in the provided data
• Real-world results can vary; misfire causes can be multiple and chassis/engine variants may influence the root cause
• If you want the most precise diagnosis, a hands-on inspection with a good scan tool and, where needed, lab tests is essential

Final recommendations

• If you experience a persistent P0304 on a 2016-2023 Toyota Tacoma, start with the simplest, most common fixes: replace the cylinder 4 spark plug and test the cylinder 4 ignition coil
• If the misfire persists after swapping the plug/coil, test the injector and check compression
• If compression is normal and the injector is not the cause, move toward vacuum leaks and then deeper mechanical inspection
• If you lack the tools or experience, consider professional diagnostics early to avoid misdiagnosis and higher repair costs

If you want, I can tailor a parts-and-labor checklist for your exact Tacoma trim (2.7L 4-cylinder vs 3.5L V6) and your region to tighten the cost estimates or create a shopping list for DIY work.