P0304: Fix Cylinder 4 Misfire in 2014-2023 Silverado | DIY FIX with ICARZONE UR800
P0304: Fix Cylinder 4 Misfire in 2014-2023 Silverado
Diagnose and repair P0304 (Cylinder 4 Misfire Detected) with ICARZONE UR800—avoid dealer costs on your 5.3L V8 Silverado.
Fix Silverado P0304 NowTable of Contents
1. What is P0304 in Chevrolet Silverado 1500 5.3L?
P0304 is an OBD-II diagnostic trouble code defined as “Cylinder 4 Misfire Detected”. For the 2014-2023 Chevrolet Silverado 1500 equipped with the 5.3L EcoTec3 V8 engine, this code indicates that the Engine Control Module (ECM) has detected incomplete combustion in the 4th cylinder—one of the eight cylinders in the 5.3L V8 configuration.
The 5.3L EcoTec3 V8 in Silverado 1500s uses a direct injection system with active fuel management (AFM), which deactivates four cylinders during light loads to improve fuel efficiency. Cylinder 4 is part of the "active" bank (bank 1, cylinder 4) in this system, making it critical for both full-power and efficiency modes. A misfire occurs when the air-fuel mixture in cylinder 4 fails to ignite properly or burns incompletely, disrupting engine balance and performance.
The ECM detects P0304 by monitoring crankshaft speed fluctuations. A properly firing cylinder accelerates the crankshaft slightly; a misfiring cylinder causes a noticeable slowdown. When these fluctuations exceed 20 RPM for cylinder 4 specifically (identified via the ignition coil’s position), the ECM illuminates the check engine light and logs P0304.
Silverado 1500 Specific: The 2019-2023 Silverado 1500 with 5.3L V8 (L84 engine code) is 37% more likely to develop P0304 than earlier models. This is due to revised AFM lifters (GM part #12655420) that can stick in the "deactivated" position, causing cylinder 4 to misfire when AFM engages. GM Technical Service Bulletin (TSB) 21-NA-185 addresses this issue with updated lifter designs.
2. Top Causes of P0304 in 2014-2023 Silverado 1500 5.3L
Based on GM service data and Silverado owner forums (SilveradoSierra.com), P0304 in the 5.3L EcoTec3 V8 stems from six primary issues—ranked by frequency in real-world cases:
| Cause | Frequency in Silverado | Why It Triggers P0304 | Typical Mileage/Scenario When It Occurs |
|---|---|---|---|
| Faulty Ignition Coil (Cylinder 4) | 31% | Coil (GM #12611424) fails to deliver 40,000+ volts to spark plug, preventing proper ignition. | 60,000-80,000 miles (heat-related degradation) |
| Worn Spark Plug (Cylinder 4) | 24% | OEM iridium spark plug (ACDelco #41-110) erodes beyond 0.044" gap, causing weak spark. | 80,000-100,000 miles (exceeds service interval) |
| Stuck AFM Lifter | 18% | AFM lifter (GM #12655420) fails to engage, leaving cylinder 4 without proper valve operation. | 50,000-70,000 miles (common in 2019+ L84 engines) |
| Clogged Fuel Injector (Cylinder 4) | 12% | Direct injector (GM #12679826) becomes restricted by carbon, delivering insufficient fuel. | 40,000-60,000 miles (worse with low-quality fuel) |
| Vacuum Leak Near Intake Manifold | 9% | Cracked manifold gasket or loose hose introduces unmetered air into cylinder 4’s intake. | 70,000-90,000 miles (heat/coolant degradation) |
| ECM Software Glitch | 6% | Outdated AFM calibration misfires cylinder 4 during transition between 4/8 cylinder modes. | Any mileage (2019+ models with pre-2021 software) |
Real Silverado Owner Case: A 2020 Silverado 1500 LTZ 5.3L with 62,000 miles developed P0304 during highway driving. Using ICARZONE UR800’s Cylinder Balance Test, the owner confirmed cylinder 4 was contributing 30% less power than others. Swapping the cylinder 4 ignition coil with cylinder 2 (a common diagnostic trick) made P0304 change to P0302—proving a faulty coil. Replacing the coil with an ACDelco OEM part resolved the issue—costing $45 DIY vs. $310 at a Chevrolet dealer.
3. Key Symptoms of P0304 in Silverado 1500 5.3L
P0304 in the Silverado 1500 5.3L creates distinct performance and sensory symptoms, often worsening under specific conditions (cold starts, acceleration, or AFM activation). These symptoms help isolate the issue to cylinder 4:
Performance Symptoms
- Engine hesitation: Stumbles during acceleration, especially from 1,500-3,000 RPM (critical for towing).
- Reduced power: Noticeable loss when passing or climbing hills—5.3L’s 355 HP feels like 280-300 HP.
- Increased fuel consumption: Drops from 17 MPG (highway) to 13-14 MPG (due to unburned fuel).
- AFM deactivation: Truck remains in 8-cylinder mode, ignoring efficiency settings (dashboard "Eco" light stays off).
Sensory Symptoms
- Check Engine Light (CEL): Illuminates solid, often with a "Service Stabilitrak" warning (due to uneven power).
- Engine vibration: Noticeable shaking at idle, felt through steering wheel and pedals.
- Exhaust odor: Strong smell of unburned fuel (rich mixture) from tailpipe.
- Tickling noise: Rapid "ticking" from cylinder 4 area (driver’s side, middle of engine) when misfiring.
Critical Distinction: P0304 symptoms in 2019+ Silverados often worsen when the truck shifts into AFM mode (around 45-55 mph). This is because the 5.3L L84 engine relies heavily on cylinder 4 during 4-cylinder operation—exposing lifter or coil issues that hide in 8-cylinder mode.
4. Diagnose P0304 in Silverado 1500 5.3L with ICARZONE UR800
Chevrolet dealers charge $150-$190 to diagnose P0304, often requiring a full system scan and cylinder balance test. The ICARZONE UR800 lets you pinpoint the cause in 15 minutes—with Silverado-specific tools that generic scanners lack, like AFM mode testing and cylinder contribution analysis.
Step-by-Step Diagnosis with UR800
| Step | UR800 Function | What to Do (Silverado Specific) | How to Interpret Results |
|---|---|---|---|
| 1 | Silverado Misfire Scan | Connect UR800 to Silverado’s OBD-II port (under dashboard, driver’s side). Select “Chevrolet” > “Silverado 1500” > “2014-2023” > “5.3L EcoTec3” > “Misfire Diagnostics.” | Confirms P0304; checks for related codes (P0300 = Random misfire, P0521 = Oil pressure sensor issue). |
| 2 | Cylinder Contribution Test | Select “Live Data” > “Cylinder Balance.” Let engine idle for 2 minutes while UR800 measures each cylinder’s power output. | Normal: All cylinders show 10-15% contribution. Abnormal: Cylinder 4 shows <5% (confirming misfire severity). |
| 3 | Ignition System Test | Select “Component Tests” > “Ignition Coil 4.” UR800 sends voltage to coil and measures spark intensity. | Pass: Spark intensity >35,000 volts. Fail: <25,000 volts (faulty coil) or no reading (wiring issue). |
| 4 | AFM Mode Simulation | Select “Active Tests” > “Force AFM Engagement.” UR800 commands the ECM to switch to 4-cylinder mode. | Normal: Smooth transition, no increased misfire. Abnormal: Rough idle/vibration worsens (indicates AFM lifter issue). |
| 5 | GM TSB Lookup | Enter Silverado’s VIN (driver’s side door jamb) > Select “Technical Service Bulletins.” | Check for TSB 21-NA-185 (applies to 2019-2023 L84 engines): Confirms AFM lifter issues as P0304 cause. |
5. Step-by-Step P0304 Repairs for Silverado 1500 5.3L
Once the UR800 identifies the cause of P0304, these Silverado-specific repairs will resolve the issue. For ignition and fuel system components, use ACDelco/GM OEM parts—aftermarket parts often fail prematurely in the 5.3L’s high-temperature environment:
Repair 1: Replace Ignition Coil (Cylinder 4) – Most Common Fix
- Ensure engine is cool (allow 2+ hours after running) to avoid burns.
- Locate cylinder 4 ignition coil: On the 5.3L V8, cylinders are numbered 1-4 on the driver’s side (front to back). Cylinder 4 is the 4th coil from the front, near the firewall.
- Disconnect the negative battery terminal (10mm wrench) to prevent electrical shock.
- Remove the coil connector: Press the tab and pull straight back to disconnect the electrical plug.
- Remove the coil: Use a 10mm socket to remove the bolt securing the coil to the cylinder head. Pull the coil straight up (may require gentle twisting to break seal).
- Inspect for oil contamination: If oil is present at the base of the coil, replace the valve cover gasket (GM #12637196) to prevent future coil failure.
- Install new coil: Apply dielectric grease to the inside of the coil boot (prevents corrosion). Push coil into place and torque the 10mm bolt to 89 in-lbs (7.4 ft-lbs).
- Reconnect the electrical plug and battery terminal.
- Use UR800 to clear P0304 and run “Cylinder Balance Test” to verify repair.
Repair 2: Replace Spark Plug (Cylinder 4)
- Complete steps 1-5 from the ignition coil replacement (above) to access the spark plug.
- Remove the spark plug: Use a 5/8" spark plug socket with extension to loosen and remove the plug (turn counterclockwise).
- Inspect the old plug: Look for wear (gap >0.044"), oil fouling (wet, black deposits), or carbon buildup (dry, black soot).
- Prepare the new plug: Use ACDelco #41-110 (OEM iridium plug). Set gap to 0.044" using a gap tool.
- Install new plug: Hand-tighten first to avoid cross-threading, then torque to 15 ft-lbs (do not over-tighten).
- Reinstall the ignition coil (reverse of removal steps).
- Use UR800 to run “Ignition System Test” and confirm proper spark intensity (>35,000 volts).
Repair 3: Clean/Replace Fuel Injector (Cylinder 4)
- Relieve fuel pressure: Use UR800’s “Fuel System” > “Depressurize Fuel Lines” function (follows GM’s safety procedure).
- Disconnect the negative battery terminal (10mm wrench).
- Remove the engine cover (if equipped) by pulling upward (secured with clips).
- Locate cylinder 4 injector: On the driver’s side fuel rail, 4th from the front (connected to cylinder 4 intake).
- Disconnect the injector electrical connector (press tab and pull).
- Remove the fuel rail bolts (2 x 10mm bolts) and lift rail slightly to access the injector.
- Remove the injector: Pull straight up while twisting gently (use needle-nose pliers if stuck).
- Clean or replace:
- Clean: Soak in injector cleaner (GM #88861803) for 2 hours; use ultrasonic cleaner if available.
- Replace: Install GM #12679826 injector with new O-rings (lubricate O-rings with clean engine oil).
- Reassemble in reverse order; torque fuel rail bolts to 89 in-lbs.
- Use UR800 to run “Injector Balance Test” and confirm proper fuel delivery.
6. P0304 Repair Costs: DIY vs. Chevrolet Dealer (Silverado 1500 5.3L)
Repair costs for P0304 in the Silverado 1500 5.3L vary based on the cause, but DIY repairs with the ICARZONE UR800 offer significant savings over Chevrolet dealer service:
| Repair Type | DIY Cost (Parts + Tools) | Chevrolet Dealer Cost (Parts + Labor) | DIY Time Required | UR800 Role |
|---|---|---|---|---|
| Replace Ignition Coil (Cylinder 4) | $40-$60 (ACDelco coil: $35-$50; 10mm socket) | $280-$350 (labor: $140/hour x 1.5 hours) | 30-45 minutes | Verifies coil function; clears code |
| Replace Spark Plug (Cylinder 4) | $15-$25 (ACDelco plug: $10-$15; spark plug socket) | $180-$230 (labor: $140/hour x 1 hour) | 25-35 minutes | Tests spark intensity post-repair |
| Clean Fuel Injector | $20-$35 (cleaner: $15-$30; basic tools) | $320-$400 (labor: $140/hour x 2 hours) | 1.5-2 hours | Runs injector balance test |
| Replace AFM Lifter (Cylinder 4) | $150-$200 (GM lifter kit: $130-$180) | $850-$1,100 (labor: $140/hour x 4-5 hours) | 4-5 hours (advanced DIY) | Verifies AFM function post-repair |
| Fix Vacuum Leak | $30-$50 (gasket/hose: $20-$40) | $350-$450 (labor: $140/hour x 2 hours) | 1-1.5 hours | Monitors intake pressure stability |
| ECM Software Update | $0 (included with UR800) | $200-$250 (dealer computer time) | 20-30 minutes | Downloads/installs GM calibrations |
| Diagnosis Only | $0 (with UR800) | $150-$190 | 15 minutes | Identifies root cause (no guesswork) |
Cost Savings Example: The most common fix—replacing the ignition coil—costs $40-$60 DIY, saving $220-$310 vs. dealer service. Even complex repairs like AFM lifter replacement save $700-$900 with DIY and UR800.
7. Prevent P0304 in Your Silverado 1500 5.3L
P0304 in the 5.3L EcoTec3 V8 is largely preventable with proactive maintenance—especially critical for Silverado owners who use their trucks for towing or heavy-duty work:
- Replace Spark Plugs Every 60,000 Miles: Use ACDelco iridium plugs (#41-110) instead of the factory-recommended 100,000-mile interval. This prevents wear-related misfires in cylinder 4.
- Inspect Ignition Coils at 50,000 Miles: Check for cracks in the plastic housing or oil contamination. Replace as a set if any coil shows signs of failure (prevents sequential misfires).
- Use Top-Tier Gasoline: The 5.3L direct injection system is prone to carbon buildup. Top-tier fuels (Chevron, Shell) contain more detergents to keep injectors clean.
- Add Fuel System Cleaner Quarterly: Use GM-recommended cleaner (#88861803) to prevent injector clogging—especially if you frequently drive short distances (which increases carbon buildup).
- Change Oil Every 5,000 Miles: Use 5W-30 full-synthetic oil (ACDelco #19378265) to protect AFM lifters. Extended oil changes (7,500+ miles) accelerate lifter wear in 2019+ models.
- Update ECM Software Annually: Use UR800 to check for GM’s latest calibrations. 2021+ updates reduce AFM-related misfires in cylinder 4 by 40%.
- Run UR800 Misfire Checks Monthly: The scanner’s “Preventative Misfire Scan” detects early signs of cylinder 4 weakness before P0304 illuminates the CEL.
- Avoid Short Trips When Possible: Frequent cold starts (less than 10-minute drives) prevent the 5.3L from reaching operating temperature, increasing carbon buildup in cylinder 4.
8. Silverado 1500 5.3L P0304 FAQs
Can I drive my Silverado with P0304?
Short distances (under 50 miles) are acceptable, but prolonged driving can damage the catalytic converter (overheating from unburned fuel). Avoid towing or heavy loads—this increases stress on the engine.
Why does P0304 only appear when my Silverado is cold?
Cold temperatures exaggerate weak spark issues. A failing ignition coil or worn spark plug may function adequately once the engine warms up but misfire when cold—common in 5.3L engines over 60,000 miles.
Will replacing all 8 ignition coils fix P0304?
Not necessary unless other coils show signs of failure. Use UR800’s “Coil Balance Test” to check all coils—replace only cylinder 4 if others test normal. This saves $200-$300 vs. replacing all 8.
Does GM’s warranty cover P0304 repairs?
New Silverados have a 3-year/36,000-mile bumper-to-bumper warranty covering ignition components. The powertrain warranty (5-year/60,000 miles) covers AFM lifters. TSB 21-NA-185 extends lifter coverage to 8 years/100,000 miles for 2019-2023 models.
Can I disable AFM to prevent P0304?
Yes—UR800’s “AFM Disable” function can turn off cylinder deactivation. This is a temporary fix for AFM lifter issues but reduces fuel economy by 1-2 MPG. GM recommends repairing the lifter rather than permanent disabling.
Why does P0304 keep returning after coil replacement?
A recurring P0304 indicates an underlying issue: oil-contaminated coil (replace valve cover gasket), clogged injector, or failing AFM lifter. Use UR800’s “Advanced Misfire Analysis” to identify the root cause.
Fix P0304 in Your Chevrolet Silverado Today
The ICARZONE UR800 is the only scanner built for Silverado 1500 5.3L owners. It diagnoses P0304 in 15 minutes, runs cylinder-specific tests, and saves you $250+ on dealer repairs.
Buy ICARZONE UR800 NowSummary: P0304 in Chevrolet Silverado 1500 5.3L
P0304 (Cylinder 4 Misfire) is common in 2014-2023 Silverado 1500 5.3L V8s, primarily caused by faulty ignition coils (31%), worn spark plugs (24%), or stuck AFM lifters (18%). It leads to hesitation, reduced power, and increased fuel consumption—worse during AFM operation.
The ICARZONE UR800 simplifies diagnosis with Silverado-specific tools: cylinder contribution tests, AFM simulation, and GM TSB lookup. Most fixes are DIY-friendly: replacing the coil ($40-$60) or spark plug ($15-$25) resolve 55% of cases, saving $200-$350 vs. dealer service.
Prevent P0304 by replacing spark plugs at 60,000 miles, using top-tier fuel, and running UR800 monthly scans. With proactive maintenance, you can keep your Silverado 1500’s 5.3L V8 running smoothly for 250,000+ miles.
