P0304 Code: Jeep Cherokee (2019-2023) - Causes, Symptoms & Fixes

Below is a comprehensive diagnostic guide for OBD-II code P0304 (Cylinder 4 Misfire Detected) as it can appear on a 2019-2023 Jeep Cherokee. Note: The real NHTSA data provided for this exact make/model/year/issue shows no owner complaints and no recalls in the database. No recalls found in NHTSA database. This guide uses general automotive knowledge for misfire diagnosis and clearly states data limitations where applicable.

Code Meaning and Severity

• P0304 = Cylinder 4 misfire detected by the engine control module (PCM).
• What it means:
  • The PCM has detected abnormal combustion in cylinder 4. This can be a transient issue or a persistent problem.
• Severity and driving impact:
  • A single, momentary misfire may not cause immediate harm, but ongoing misfires can cause rough running, reduced power, higher fuel consumption, and potential damage to the catalytic converter due to unburned fuel entering the exhaust.
  • If the misfire persists, limit driving to avoid catalytic converter overheating or potential engine damage. Address promptly.

Common Causes on Jeep Cherokee (2019–2023)

• Ignition-related
  • Faulty spark plug in cylinder 4 (worn, fouled, incorrect gap).
  • Bad ignition coil or coil-on-plug failure for cylinder 4.
  • Damaged ignition coil boot or wiring/connectors to the coil.
• Fuel-system related
  • Clogged or malfunctioning fuel injector for cylinder 4.
  • Low fuel pressure or fuel-delivery issue affecting cylinder 4.
• Air and vacuum
  • Vacuum leak around intake manifold or gasket near cylinder 4, or around PCV system.
  • Intake manifold runner control issue or duct leak affecting cylinder 4.
• Mechanical and metering
  • Low compression in cylinder 4 due to valve issues, piston ring wear, or compromised head gasket.
  • Faulty PCM software or wiring faults (less common, but possible).
• Other
  • Dirty or contaminated cam/ crank signals causing misfire perception (rare).
  • Injector/igniter wiring harness damage or corrosion.

Symptoms

• Engine MIL (check engine light) on with P0304 stored or pending.
• Rough idle or vibration when the engine is idling.
• Noticeable loss of power or reduced acceleration.
• Sudden or intermittent engine stumble during acceleration.
• Increased or abnormal fuel consumption.
• In some cases, misfire may be more noticeable at cold start or under load.
• No obvious signs? A misfire can be intermittent; further diagnosis required.

Diagnostic Steps (Structured, step-by-step)

Before you begin, ensure you have a decent OBD-II scanner that can read live data and misfire counters, as well as basic hand tools.

A. Confirm and gather data

• Retrieve codes with an OBD-II scanner: confirm P0304 and check for related codes (P0300, P0301, P0302, P0303, P0305…).
• Check the freeze frame data and any misfire counter if your scanner provides live data.
• Note symptoms and operating conditions when the misfire occurs (engine cold vs hot, load, RPM range).

B. Visual inspection

• Inspect spark plug 4: condition, gap, fouling, oil contamination, or damage.
• Inspect coil-on-plug 4 and its connector for corrosion, cracks, or loose connections.
• Inspect wiring to injector 4 and coil 4 for damaged insulation, corrosion, or bent pins.
• Check for obvious vacuum leaks around the intake manifold (gaskets, hoses, PCV).
• Inspect for signs of dash warning indicators (e.g., coolant temperature oddities) that could affect engine operation.

C. Ignite and fuel-supply checks

• Spark: Swap the ignition coil from cylinder 4 with another cylinder (e.g., cylinder 1). Clear codes and test drive to see if the misfire moves to the new cylinder. If P0301 appears, the issue is likely coil 1; if P0304 remains, coil 4 is likely faulty.
• Spark plug: Remove and inspect cylinder 4 plug. If fouled or worn, replace with the correct heat-range plug and proper gap.
• Fuel injector: Listen for injector operation on cylinder 4 with a mechanic’s stethoscope or acoustic probe while the engine runs. Measure injector resistance (specs vary by engine) and compare to other cylinders.
  • If injector is sticky or not opening properly, consider cleaning or replacement.
• Fuel pressure: Verify fuel pressure spec for your Cherokee engine (2.4L or 3.2L). Low fuel pressure can cause misfires; test with a gauge and compare to spec.
• Compression test: Perform a compression test on cylinder 4 and compare with the other cylinders. Low compression indicates mechanical issues (valve, piston, head gasket).

D. Advanced checks if needed

• Swap components: If stepping through coil and injector tests indicates a particular component, perform a targeted replacement.
• Scan data for misfire timing and RPM-related patterns to see if the misfire correlates with specific RPM ranges.
• Electrical/PCM: If all mechanical and component checks pass yet misfire persists, consider PCM data/wiring and software update eligibility (consult dealer or a shop with diagnostic software).

E. Decide on repair approach

• If a defective spark plug or coil is found, replace them (often the simplest fix).
• If injector is faulty, clean or replace as needed.
• If vacuum leak or gasket issue is found, repair the leak.
• If compression is low, assess mechanical repair options (valve job, ring/piston work, or engine replacement).

Note: The data provided for this specific model/year indicates no official recalls or complaints in the referenced NHTSA data set. No recalls found in NHTSA database. Use this diagnostic guide as general guidance; always corroborate with vehicle-specific service information and current dealer/repair spec sheets.

Related Codes

• P0300: Random/Multiple Cylinder Misfire Detected.
• Other P030x codes may appear if multiple cylinders are affected (P0301, P0302, P0303, P0305, etc.).
• If P0300 is present along with P0304, consider a shared root cause (e.g., ignition system or fuel pressure issue that affects multiple cylinders).
• If additional codes indicating fuel system or ignition faults appear (e.g., P017x for fuel trim, P010x for MAF/MAP sensors, P0171/P0172 lean/rich conditions), broaden the diagnostic scope accordingly.

Repair Options and Costs (2025 Prices)

Note: Prices vary by region, shop, engine variant (2.4L I4 vs 3.2L V6), and labor rates. The ranges below are typical ballpark figures for common fixes on a 2019–2023 Jeep Cherokee.

• Spark plug replacement (cylinder 4)

  • Parts: $6–$25
  • Labor: 0.3–1.0 hours
  • Estimated total: $60–$180
  • If you replace all plugs: $100–$400 (parts + labor)

• Ignition coil (cylinder 4)

  • Parts: $40–$120
  • Labor: 0.5–1.0 hours
  • Estimated total: $60–$180

• Fuel injector (cylinder 4)

  • Parts: $100–$220
  • Labor: 0.5–1.0 hours
  • Estimated total: $160–$360
  • Note: Cleaning injectors can be cheaper (labor-assisted cleaning) but may not resolve all issues.

• Fuel system issues (low fuel pressure)

  • Fuel pump replacement (if necessary): $350–$900 (parts + labor)
  • Fuel pressure regulator and hoses: $120–$350 (parts + labor)

• Vacuum/air-leak repair around cylinder 4

  • Parts: $20–$100
  • Labor: 1.0–3.0 hours
  • Estimated total: $120–$450

• Compression-related repairs

  • Simple head gasket/valve seal fixes: $800–$2,500 (parts + labor; varies widely)
  • Major engine work or rebuild: $2,000–$5,000+ (depending on extent)

• Miscellaneous

  • Scanner and diagnostic time: $60–$150
  • Wiring/connector repair: $50–$200 (parts + labor as needed)

Important: These are representative ranges. Exact pricing depends on your engine (2.4L I4 vs 3.2L V6), local labor rates, and whether you replace just cylinder 4 components or do a broader package (e.g., all plugs and coils).

DIY vs Professional

• DIY feasibility:
  • Simple fixes (replacing a misfiring cylinder 4 spark plug or swapping a bad coil with a known-good unit) are typically within the capability of a capable DIYer with basic tools.
  • Basic fuel-delivery checks (fuel pressure testing, injector resistance checks) can be done with the right tools, but may be challenging for beginners.
  • Be mindful of safety: working with fuel systems and high-voltage ignition components requires care.
• Professional service:
  • Recommended for persistent misfires, uncertain diagnostics, or suspected mechanical issues (low compression, valve problems, or internal engine damage).
  • A shop can perform a controlled coil/plug swap test, fuel-pressure test, injector testing, compression test, and wiring checks with proper tooling.

Prevention

• Regular maintenance according to the owner’s manual:
  • Replace spark plugs at the recommended interval with the correct platinum/iridium type and correct gap for your engine.
  • Replace ignition coils if there are signs of wear or if the vehicle shows a misfire pattern tied to a specific cylinder.
  • Use quality fuel and consider periodic injector cleaning (as recommended by the service schedule or if you notice performance issues).
  • Keep air intake clean; replace air filter on schedule to avoid lean misfire symptoms.
  • Maintain vacuum lines and PCV system; address any cracks or leaks promptly.
  • Monitor fuel pressure and injector performance during routine service or if you notice rough running or reduced power.
• Listen for changes in engine feel: a sudden rough idle or power drop can indicate a developing issue with cylinder 4 components and should be checked early.
• Address software updates if a dealer or mechanic notes a PCM calibration update; although not a cure-all, software revisions can fix misfire-related calibration anomalies in some cases.

Data limitations

• The provided real-world NHTSA data for 2019–2023 Jeep Cherokee shows No recalls found in NHTSA database and No owner complaints for this exact code combination. No recalls found in NHTSA database. This means there is no official recall or complaint data to reference for this exact scenario in the given data. The diagnostic guidance above uses general automotive knowledge applicable to P0304 across many modern engines, including those used in Jeep Cherokee variants.
• If you want the most precise information for your exact engine (2.4L vs 3.2L, turbo variants, etc.), consult your vehicle’s service manual, factory service information, or a dealer diagnostic portal for recommended specs and procedures specific to your VIN.