P0304 on 2010-2013 Chevrolet Express: Cylinder 4 Misfire Causes and Fixes

What's Unique About the 2010-2013 Chevrolet EXPRESS

For the 2010-2013 Express vans, particularly the 2010 model year, General Motors issued a Technical Service Bulletin (TSB #PIP4819A) regarding misfire codes, including P0304. This bulletin specifically advises technicians to inspect for and replace loose-fitting spark plug wires, indicating a known issue with the connection between the wire and the spark plug or coil. Furthermore, the 5.3L and 6.0L V8 engines are equipped with Active Fuel Management (AFM), also known as Displacement on Demand (DoD). This system deactivates cylinders 1, 4, 6, and 7 under light loads to improve fuel economy. The hydraulic lifters associated with these cylinders are a known major failure point; they can become stuck or collapse, preventing the valve from opening and causing a persistent misfire on that cylinder, making P0304 a very common code related to this mechanical issue. A collapsed AFM lifter may also present with a ticking noise.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Rough or shaking idle
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Flashing or solid Check Engine Light
• Smell of unburned fuel from the exhaust
• Reduced fuel economy
• A distinct ticking or tapping sound from the engine that increases with RPM (often indicates a lifter issue).

Most Likely Causes

1. Loose or Faulty Spark Plug Wire 🔴 High Probability A specific TSB (PIP4819A) was issued for 2010 models for this exact problem, suggesting a higher-than-normal failure rate or fitment issue from the factory.
   How to confirm: Visually inspect the spark plug wire for cylinder 4 for damage, corrosion, or a loose fit at the spark plug and ignition coil. Ensure it 'clicks' firmly into place. You can also measure the wire's resistance with a multimeter; a very high or infinite reading indicates a bad wire.
   Typical fix: Replace the spark plug wire set. It's best practice to replace all wires at the same time.
   Est. part cost: $50-$100
2. Worn or Fouled Spark Plug 🔴 High Probability
   How to confirm: Remove the spark plug from cylinder 4. Inspect it for wear (rounded electrode), carbon buildup, oil fouling, or cracks in the porcelain. A simple diagnostic step is to swap the cylinder 4 spark plug with one from another cylinder (e.g., cylinder 2). If the misfire code changes to P0302, the spark plug is the culprit.
   Typical fix: Replace the spark plug. It is highly recommended to replace all spark plugs at the same time to maintain consistent performance. The correct gap for ACDelco 41-110 Iridium plugs is typically 0.040 inches.
   Est. part cost: $8-$20 per plug
3. Failing Ignition Coil 🟡 Medium Probability
   How to confirm: Swap the ignition coil from cylinder 4 with the coil from another cylinder (e.g., cylinder 2). Clear the codes and run the engine. If the code changes to P0302, the ignition coil is faulty.
   Typical fix: Replace the faulty ignition coil. While you can replace just one, if the vehicle has high mileage, consider replacing them as a set.
   Est. part cost: $40-$75 per coil
4. Collapsed AFM/DoD Lifter (V8 Engines Only) 🟡 Medium Probability The 5.3L and 6.0L V8s use AFM, and cylinder 4 is one of the cylinders that is deactivated. The specialized lifters for these cylinders are a very common failure point, leading to misfires.
   How to confirm: Listen for a loud, rhythmic ticking/tapping noise from the passenger side valve cover area. Remove the valve cover and start the engine (or have an assistant crank it with the fuel system disabled). Visually confirm if the rocker arms for cylinder 4 are moving significantly less than the others. A compression test on cylinder 4 may show low or zero compression. TSBs like PIP4568 provide diagnostic guidance for this issue.
   Typical fix: This is a major repair. It involves removing the cylinder head to replace the faulty lifters 🎬 Watch this walkthrough on replacing lifters and removing the cylinder head. on that bank. It is highly recommended to replace all AFM lifters, and often the camshaft is replaced at the same time due to potential damage from the failed lifter. Many owners opt for an 'AFM delete kit' to prevent future failures.
   Est. part cost: $300-$800 for lifters, gaskets, and bolts. Up to $1500+ if including a new camshaft and other components.
5. Clogged or Faulty Fuel Injector ⚪ Low Probability
   How to confirm: Use a mechanic's stethoscope or a long screwdriver to listen to the injector on cylinder 4. It should have a consistent, audible clicking sound. Compare its sound to an adjacent injector. No sound or an irregular sound suggests a problem. You can also swap injectors between cylinders to see if the misfire follows, though this is more labor-intensive.
   Typical fix: Replace the faulty fuel injector. The fuel rail may need to be removed for access.
   Est. part cost: $50-$120

Rare But Worth Checking

• Intake Manifold Gasket Leak: The plastic intake manifolds on Vortec engines can develop vacuum leaks near a specific cylinder, leaning out the air/fuel mixture and causing a misfire. A smoke test is the best way to confirm this.
• Low Engine Compression: Internal engine issues like a worn piston ring, a burnt valve, or a damaged cylinder head can cause a loss of compression, leading to a misfire. For the V8 engines, low compression is very often a direct result of a collapsed AFM lifter. A compression test is required to diagnose this.

Diagnosis Steps

1. Read the trouble codes with an OBD-II scanner to confirm P0304 and check for any other codes.
🎬 Watch: How to quickly diagnose a P0304 misfire with a code reader.
2. For V8 engines, identify cylinder 4: It is the second cylinder from the front on the passenger side.
3. Visually inspect the spark plug wire for cylinder 4. Ensure it is securely connected at both the ignition coil and the spark plug. Check for any signs of arcing (white marks) or physical damage. Per TSB #PIP4819A, this is a critical first step.
4. To easily isolate the cause, swap components. Start by moving the cylinder 4 spark plug to cylinder 2. Clear the codes and drive. If the code returns as P0302, the spark plug is bad.
5. If the code remains P0304, move the cylinder 4 ignition coil to cylinder 2 (after returning the spark plug). Clear codes and drive. If the code is now P0302, the coil is bad.
6. If the code is still P0304, listen carefully to the engine, especially the passenger side valve cover area. A distinct, rhythmic ticking noise strongly suggests a collapsed AFM lifter.
7. Check the fuel injector for cylinder 4 by listening for a steady clicking sound with a stethoscope or long screwdriver.
8. If a lifter issue is suspected, the next step is a compression test on cylinder 4. A low or zero reading points towards a mechanical problem, very likely the lifter/camshaft.
9. If all else fails, a smoke test can be performed to check for vacuum leaks, such as from an intake manifold gasket.

Parts You'll Likely Need

• Spark Plug Wire Set (OEM #9748UU) — A known issue for this vehicle range, as documented in TSB #PIP4819A. Wires can degrade over time or have poor connections, causing a weak spark.
  Trusted brands: ACDelco
  OEM price range: $60-$90
  Aftermarket price range: $45-$75
• Iridium Spark Plug (OEM #41-110) — Spark plugs are a routine maintenance item and a primary cause of misfires. A worn or fouled plug cannot create a strong enough spark for proper combustion.
  Trusted brands: ACDelco, NGK
  OEM price range: $12-$20
  Aftermarket price range: $8-$15
• Ignition Coil (OEM #12699382) — The ignition coil provides the high voltage needed to create a spark. Over time, heat and vibration can cause the coil to fail, leading to a misfire.
  Trusted brands: ACDelco, Delphi
  OEM price range: $60-$80
  Aftermarket price range: $40-$65
• AFM Hydraulic Roller Lifter Set (OEM #12648846 (Set of 4 AFM lifters)) — A very common failure point on 5.3L and 6.0L V8s, causing a P0304. If one has failed, it is best practice to replace all AFM lifters in the engine.

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or affects other cylinders, a P0300 (Random/Multiple Cylinder Misfire) code may be stored alongside P0304. The TSB #PIP4819A notes that P0300 often appears with specific cylinder misfire codes. A failing AFM system can also initially present as a P0300.
• Service Stabilitrak / Service Traction Control — On many GM vehicles, an engine misfire will disable the traction control and Stabilitrak systems as a safety precaution, as the engine is not running as expected. This is a symptom, not a separate problem.

Technical Service Bulletins (TSBs) & Recalls

• PIP4819A: Addresses engine misfires (P0300-P0308) and directs technicians to inspect and replace loose spark plug wires.
• PIP5163A: Discusses diagnosis for engine misfires, oil consumption, or blow-by, which can be related to cylinder wall or piston issues, though less common.
• PIP4568 (and subsequent versions): Provides diagnostic information related to collapsed AFM lifters causing misfires and/or noise.

Platform-Specific Known Issues

• TSB #PIP4819A specifically calls out loose spark plug wires as a cause for misfires on 2010 models. This should be the first inspection point.
• For 5.3L and 6.0L V8s, failure of the Active Fuel Management (AFM) lifter for cylinder 4 is a very common and well-documented cause of a P0304 code, often accompanied by a ticking noise.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Resistance — expected: 0.4 to 0.6 ohms. Failure: A reading of 0 ohms (short) or infinite/OL (open).
• Ignition Coil Secondary Resistance — expected: 5,000 to 7,200 ohms. Failure: A reading significantly outside this range, or infinite/OL, indicates a faulty coil.
• Fuel Injector Resistance — expected: 11.0 to 16.0 ohms (for high-impedance injectors). All injectors should be within 0.5 ohms of each other.. Failure: An injector reading significantly different from the others, or showing 0/OL, is faulty.
• Fuel Pressure (Key on, Engine off and at Idle) — expected: 55 to 62 PSI for 5.3L V8 models.. Failure: Pressure below 50 PSI, especially under load, indicates a weak fuel pump or clogged filter.

Scan Tool Commands That Help

• Tech2 / GDS2 (GM Dealer Scanners): Cylinder Power Balance Test — This test allows a technician to view the real-time contribution of each cylinder to the crankshaft's speed. A graph will clearly show if cylinder 4 is underperforming compared to the others, confirming the misfire is happening live. It helps differentiate a constant misfire from an intermittent one.
• Tech2 / GDS2 (GM Dealer Scanners): Injector Kill / Disable — This bidirectional command allows the user to shut off the fuel injector for cylinder 4. If there is no change in engine RPM or smoothness when cylinder 4's injector is disabled, it confirms that cylinder was not contributing in the first place, pinpointing the misfire.

Wiring & Ground Locations

• G102 — Located at the left rear of the engine.. This is the primary ground point for all 8 ignition coils. A loose or corroded connection here can cause weak or intermittent spark on multiple cylinders, including cylinder 4, leading to misfires.
• G103 — Located on the cowl in the left rear of the engine compartment, often near the brake booster.. This ground serves the Engine Control Module (ECM) and Body Control Module (BCM). A poor connection can cause a variety of erratic engine management issues, including phantom misfire codes.
• Ignition Coil Connector — On the ignition coil for cylinder 4.. The 4-pin connector provides power, ground, and the trigger signal from the ECM. The pink wire (Pin B on some models) should have 12V+ with the key on. The black wire (Pin C) is the low reference/ground. The third wire is the trigger signal from the ECM. Verifying power and ground here is essential before condemning a coil.

Real Owner Repair Stories

• LS1Tech Forum User (Vehicle with a 6.0L V8 engine experiencing a P0304.) — Persistent misfire on cylinder 4, rough idle, and check engine light.
  ❌ Tried (didn't work) Replaced spark plug, Replaced spark plug wire, Swapped ignition coil with a known good one
  ✅ What actually fixed it The owner removed the valve cover and discovered a broken valve spring on cylinder 4. Replacing the broken spring and the valve seals resolved the misfire.
• Chevrolet Forum User (2002 Suburban with Vortec V8 (similar engine architecture).) — Misfire codes and general running issues.
  ❌ Tried (didn't work) Multiple part replacements.
  ✅ What actually fixed it The user found a GM Technical Service Bulletin referencing ground G103. After locating and cleaning the ground connection at the left front of the engine block (part of the main negative battery cable harness), the misfire issues were resolved.

OEM Part Supersession History

• Various older AFM lifter part numbers (e.g., 12576400) → 12648846 — The original AFM lifters had a high failure rate. The updated part number represents a revised design intended to improve durability and prevent collapsing or sticking.
  Heads up: When replacing failed AFM lifters, it is critical to use the correct, updated part. Using old stock or non-spec parts will likely lead to a repeat failure. It is recommended to replace all AFM lifters at once, not just the single failed one.

Model Year Variations Within This Range

• 2010+: In 2010, the 6.0L V8 engine was updated from the LY6 to the L96. The primary difference was the addition of Flex Fuel (E85) capability to the L96. While mechanically very similar, this involves different fuel injectors and ECM tuning. The L96 continued to use Variable Valve Timing (VVT) like the LY6.