P0304 Code: Chevrolet Silverado (2019-2024) - Causes, Symptoms & Fixes

Here is a comprehensive diagnostic guide for OBD-II code P0304 (Cylinder 4 Misfire) specifically for 2019–2024 Chevrolet Silverado.

Important data note

• Based on the provided NHTSA data excerpt: No owner complaints found for this make/model/year/issue, and No recalls found in the NHTSA database.
• This guide combines the data you provided with general automotive knowledge. If a dealer bulletin or another official source exists outside the provided data, it isn’t cited here.

CODE MEANING AND SEVERITY

• What P0304 means: The powertrain control module (PCM) has detected a misfire on cylinder 4.
• Why it’s a concern: A misfire reduces engine power, can cause rough idling, and may lead to increased exhaust emissions or fuel dilution of oil if severe. Prolonged or repeated misfires can damage the catalytic converter or other exhaust components and, over time, can harm engine internals if left unaddressed.
• Typical progression: If the issue isn’t fixed, you may see the MIL (check engine light) stay on, and ongoing misfires can worsen fuel economy and performance.

COMMON CAUSES ON CHEVROLET SILVERADO (2019–2024)

Note: This section uses general, model-relevant possibilities for Silverado engines in this era (e.g., 5.3L V8, 6.2L V8, 2.7L Turbo, 3.0 Duramax). The cylinder-specific nature points to cylinder 4, but many root causes are common across cylinders.

Likely causes

• Faulty spark plug in cylinder 4 (worn, fouled, oil-fouled, incorrect gap, or loose/poorly seated)
• Faulty ignition coil for cylinder 4 (coil pack or primary/secondary winding issue; damaged boots/wiring)
• Faulty or sticking fuel injector for cylinder 4 (open/short, clogged, or seating issue)
• Wiring or connector problems to the coil or injector on cylinder 4 (damaged harness, corroded connector, loose connection)
• Vacuum leak or intake manifold gasket issue near cylinder 4 (unmetered air causing misfire)
• Low compression in cylinder 4 (valve/seal problems, piston ring wear, head gasket issue) – less common but possible
• Carbon buildup or intake valve issues (especially on direct-injection engines) affecting cylinder 4
  -Fuel delivery or pressure problems affecting one cylinder (more likely if multiple misfire codes appear or fuel trim is abnormal)
• Active Fuel Management (AFM) or cylinder deactivationrelated conditions (more common on engines with AFM/LFA; can manifest as misfire if a deactivated cylinder isn’t switching properly)
• PMD/PCM-related faults are possible but less common; usually accompanied by other codes

Notes on diagnostics specific to Silverado options

• Direct injection systems (some Silverado engines) can have carbon buildup on intake valves contributing to misfire over time.
• If your Silverado is equipped with AFM, be mindful that cylinder deactivation mechanisms can contribute to misfire-like symptoms if lifters or switching components malfunction.

SYMPTOMS YOU MIGHT NOTICE

• MIL illumination with P0304 code
• Rough idle or engine shake, especially at idle or low RPM
• Noticeable loss of power or sluggish acceleration
• Reduced or uneven engine performance under load
• Slight increase in fuel consumption
• Possible accompanying codes: P0300 (random/multiple misfire) or other P030x codes for different cylinders

DIAGNOSTIC STEPS (systematic, logical approach)

Safety first: perform all checks with the engine off when inspecting electrical connectors; allow the engine to cool if touching spark plugs or ignition components.

A. Confirm and scope

• Retrieve current DTCs and freeze frame data with a scan tool.
• Confirm there are no other misfire-related codes (P0300, P0301, P0302, P0303, P0305, P0306, P0307, P0308) that could indicate a multi-cylinder issue or a shared cause.
• Note fuel trim values (short-term and long-term) and engine load/RPM at the time of misfire.

B. Visual inspection

• Inspect spark plug for cylinder 4: signs of wear, fouling, oil deposits, or improper gap. Ensure the plug is the correct type and installed with the proper torque.
• Inspect ignition coil and coil boot for cylinder 4: cracks, carbon tracking, moisture, and proper seating. Check the coil connector for corrosion or bent pins.
• Inspect fuel injector for cylinder 4: look for signs of leaking injector or damaged electrical connector or harness.

C. Quick swap/verification tests (once safe to do so)

• Swap the ignition coil from cylinder 4 to another cylinder (e.g., cylinder 2) and clear codes. If P0302 (or the target cylinder) now presents, the coil is likely faulty.
• If possible, swap the spark plug from cylinder 4 with another cylinder to see if the misfire follows the plug. If the misfire moves, the plug is suspect; if it stays on cylinder 4, focus on the coil or injector or downstream causes.

D. Electrical and injector checks

• Measure the resistance of the ignition coil primary/secondary for cylinder 4 (compare to spec). A significantly out-of-range reading indicates a faulty coil.
• Test the coil/igniter wiring harness for continuity and resistance. Check for damaged insulation, shorts to ground, or open circuits.
• Test the fuel injector for cylinder 4: resistance check (spec varies by injector; compare to service spec), and listen for injector operation with a mechanic’s stethoscope or by using a noid light if applicable.
• Inspect injector harness and connector for corrosion, bent pins, or loose fit.

E. Fuel and air delivery checks

• Check fuel pressure with the engine running at idle and at higher RPMs; compare to the Silverado’s spec for your engine (e.g., ~40–60+ psi for many GM systems; exact spec depends on engine). A failing high- or low-pressure fuel pump/regulator could cause misfires.
• Check for vacuum leaks around intake manifold and cylinder 4 area (gaskets, hoses). A smoke test is an effective method to identify leaks.
• Check for excessive or lean fuel trim (short-term/long-term) that could indicate injector problems, vacuum leaks, or MAF/MAF sensor issues.

F. Mechanical compression check

• Perform a compression test on cylinder 4 and compare with the other cylinders. Low compression points to mechanical issues (valve seating, ring, or head gasket). If compression is low, further diagnosis or a leak-down test may be warranted.

G. Additional checks

• If you have access to misfire data, review misfire counters at various engine loads. A persistent misfire on cylinder 4 across loads supports circuitry or mechanical causes rather than a simple plug issue.
• Consider cam position sensor or crank sensor data if multiple cylinders show misfire or erratic timing, though these are less common single-cylinder culprits for P0304.

H. Decision point

• If a single simple component is identified (spark plug, coil, or injector), replace with OEM or equivalent quality parts and re-test.
• If no single faulty component is found but misfire persists, consider more thorough mechanical checks (valve/seat, piston ring, or gasket) or PCM-related issues. In some cases, software/EPROM updates or recalibration can be beneficial, but confirm through proper service channels.

RELATED CODES

• P0300: Random/Multiple Misfire Detected
• 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
• Note: P0304 is cylinder 4 misfire; other cylinder codes may occur in conjunction if multiple cylinders are affected.

REPAIR OPTIONS AND COSTS (2025 PRICES)

Prices vary by region, shop rates, and exact engine options. The figures below are typical ranges you might expect as of 2025 and are intended to help you plan. “DIY” costs reflect part prices only; “Shop” costs include labor.

A. Quick fixes and common fixes

• Spark plug replacement (cylinder 4 only if you’re addressing just that plug)

  • Parts: $2–$15
  • Labor (swap plug, often bundled with coil check): $40–$120
  • Notes: If the plug is fouled or damaged, replacing it is inexpensive and often effective.

• Ignition coil replacement (cylinder 4)

  • Parts: $40–$120
  • Labor: $60–$150
  • Notes: If the coil shows resistance or replacement tests indicate a bad coil, this is commonly effective.

• Fuel injector for cylinder 4 replacement

  • Parts: $80–$250
  • Labor: $150–$450
  • Notes: If injector is clogged or leaking, replacement is a typical fix. If the injector is hard to access, labor costs rise.

B. Moderate fixes (if diagnostics indicate a single problematic component)

• Fuel injector cleaning (not always effective for sticky injectors on direct-injection engines)

  • Parts: $10–$50 (chemical cleaners)
  • Labor: $0–$60 (if performed as a DIY service; professional-only cleaning typically priced around $60–$150)
  • Notes: Cleaning is less reliable for direct-injected engines and when the injector is physically damaged.

• Spark plug and coil kit (if both coil and plug were found suspect)

  • Parts: $60–$150 (for both parts)
  • Labor: $60–$150
  • Notes: A combined fix is common if both components show wear.

C. More extensive or mechanical issues (less common for P0304 alone)

• Compression-related repairs (valve seating, head gasket, piston rings)
  • Parts: several hundred to several thousand dollars
  • Labor: 3–10+ hours depending on engine configuration
  • Notes: Requires significant teardown; often aligns with low compression findings.

D. Miscellaneous costs and considerations

• Diagnostic fee (if not included in a repair): $80–$150 in many shops
• PCM/software updates (if advised by dealer or tech)
  • Parts: minimal or none
  • Labor: $80–$220 depending on the vehicle and update
  • Notes: Software updates can sometimes address misfire edge cases but are not a guaranteed fix.

DIY vs PROFESSIONAL

• DIY approachable steps (if you’re comfortable with basic auto repair):

  • Start with a visual inspection of cylinder 4 spark plug, boot, and coil; swap coil or plug to verify misfire follows the component.
  • Replace spark plug if fouled or worn; replace coil if testing indicates a bad coil.
  • Use a fuel pressure gauge and perform a basic injector test if you’re comfortable with more advanced tools.
  • Pros: Low cost if you catch a simple issue; quick wins.
  • Cons: Misfire causes can be electrical, mechanical, or fuel-system related; some tests require special tools and experience.

• When to go professional:

  • Misfire persists after swapping plug/coil or if you observe low compression on cylinder 4.
  • Difficulty diagnosing fuel pressure, injector health, or vacuum leaks.
  • Suspected mechanical issues (valve seating, head gasket, piston rings) or AFM/lifter concerns.
  • You don’t have access to proper diagnostic equipment (compression tester, fuel pressure gauge, scope, etc.).
  • Complexity due to direct injection systems or newer engine architectures.

PREVENTION

• Regular maintenance per GM schedule:
  • Replace spark plugs at recommended intervals with the correct heat range and torque.
  • Replace ignition coils as recommended or if you notice misfire symptoms, coil degradation, or coil failure indicators.
    Inspect and clean or replace fuel injectors as needed (especially on direct-injection engines prone to deposits).
• Use quality fuels and, when appropriate, fuel system cleaners that are compatible with direct injection engines. Avoid fuels with excessive ethanol or contaminants.
• Address AFM-related concerns if your Silverado uses cylinder deactivation:
  • Periodic driving that includes highway speeds can help keep lifters and deactivation hardware functioning; if you notice AFM-related symptoms, discuss with your technician whether AFM-related maintenance or conversion (if applicable) is appropriate.
• Monitor engine health:
  • Keep up with oil changes using the correct grade and viscosity for your engine.
  • Address oil consumption issues promptly to avoid oil making its way into the combustion chamber, which can foul plugs/coils.
  • Periodically inspect vacuum hoses and intake gaskets for leaks.
• Quick follow-up testing:
  • If you’ve resolved P0304 with a component replacement, clear codes and re-check after a short test drive to confirm the issue is resolved.
• Data limitations:
  • The provided data shows no recalls or complaints for this exact scenario in NHTSA’s database. That doesn’t exclude the possibility of other fixes or advisories outside that data, but we’re not citing non-provided sources here.