P0308 on 2009-2016 Chevrolet Silverado 3500: Cylinder 8 Misfire Causes and Fixes

What's Unique About the 2009-2016 Chevrolet SILVERADO 3500

The 6.0L V8 engine (LY6/L96) in this generation of Silverado HD trucks is known for its durability, but it has specific weaknesses that can lead to a P0308 code. Beyond common ignition part failures, these engines can be susceptible to valvetrain problems. Manufacturer bulletin #PIP4138R, which was superseded by #19-NA-219, specifically mentions that a persistent misfire can be caused by a worn camshaft lobe or a collapsed lifter, which is a more involved mechanical repair. This is especially true for the related 5.3L and some 6.0L engines equipped with Active Fuel Management (AFM), where the specialized collapsing lifters are a well-documented failure point that can lead to misfires and engine noise. While the heavy-duty 6.0L L96 engine in the 3500 series did not typically have AFM, the underlying engine architecture shares these potential cam/lifter vulnerabilities.

Diagnostic Flowchart

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

Generation note: The 2009-2016 year range covers two Silverado generations: the GMT900 (2009-2014) and the K2XX (2015-2016). The primary gasoline engine remained the 6.0L V8 (LY6, then L96), but part numbers for ignition components may differ. For example, the recommended ACDelco Iridium spark plug for a 2011 is 41-162, while a 2015 often uses 41-110. The underlying causes for a P0308 code are largely the same for both generations.

Symptoms You May Notice

• Rough or shaking idle
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Flashing or solid Check Engine Light
• Engine ticking, chirping, or squeaking noise (if related to lifter/camshaft)
• Smell of raw fuel from the exhaust
• Service Stabilitrak/Traction Control warning light may also illuminate

Most Likely Causes

1. Worn or Fouled Spark Plug 🔴 High Probability Spark plugs are a routine maintenance item. The recommended replacement interval is around 100,000 miles for iridium plugs. Accessing cylinder 8 is difficult due to its location at the rear passenger side, so it may be neglected during service.
   How to confirm: Remove the spark plug from cylinder 8. Inspect for a worn-down electrode, heavy carbon buildup, oil fouling, or cracks in the ceramic insulator. The recommended gap is 0.040 inches, but do not attempt to gap fine-wire iridium plugs.
   Typical fix: Replace the spark plug. It is best practice to replace all 8 spark plugs at the same time for balanced engine performance. Many owners remove the front passenger wheel and inner fender liner for better access to cylinder 8.
   Est. part cost: $8-$20 per plug
2. Failed Spark Plug Wire 🔴 High Probability TSB #PIP4819A specifically calls out inspecting for loose spark plug wires. Wires are exposed to high heat and can degrade, crack, or have their connections become loose over time, especially for cylinder 8 which is tucked in a high-heat area.
   How to confirm: Visually inspect the wire for any signs of cracking, burning, or corrosion at the boot. A definitive test is to swap the cylinder 8 wire with another cylinder (like cylinder 6) and see if the misfire code moves to P0306.
   Typical fix: Replace the faulty spark plug wire. It is recommended to replace the entire set of 8 wires. ACDelco Professional set 9748UU is a common replacement.
   Est. part cost: $60-$90 for a quality set
3. Failed Ignition Coil 🟡 Medium Probability The coil-on-plug units are subjected to constant heat and vibration. Cylinder 8's location at the rear of the engine bay can make it susceptible to heat soak, potentially leading to premature failure.
   How to confirm: The most common diagnostic step is to swap the ignition coil from cylinder 8 with another cylinder (e.g., cylinder 6). Clear the codes and run the engine. If the code changes to P0306, the coil is bad.
   Typical fix: Replace the faulty ignition coil. If the coils are original and the vehicle has high mileage, replacing all 8 is a preventative measure.
   Est. part cost: $40-$80 per coil
4. Clogged or Faulty Fuel Injector ⚪ Low Probability Fuel injectors can become clogged with deposits over time, or fail electrically. This is not specific to this platform but is a possibility on any higher-mileage engine.
   How to confirm: Listen to the injector with a mechanic's stethoscope; it should make a consistent clicking sound. You can also use a 'noid light' to confirm the injector is receiving an electrical signal. Swapping the injector with another cylinder is also possible but is more labor-intensive.
   Typical fix: Clean or replace the fuel injector for cylinder 8. It is often recommended to replace all 8 injectors at once to ensure a balanced fuel system.
   Est. part cost: $50-$120 per injector

Rare But Worth Checking

• Worn Camshaft Lobe or Failed Lifter: This is a known, serious mechanical issue cited in TSB #PIP4138R (now #19-NA-219). If ignition and fuel system checks do not resolve the P0308 code, especially if accompanied by a persistent ticking or squeaking noise, this should be investigated. A worn cam lobe will result in reduced valve lift, which can be measured at the pushrod. This is a common failure on GM V8s of this era, particularly those with Active Fuel Management (AFM), though non-AFM engines can also be affected.
• Coolant Leak onto Ignition Components: A well-documented issue is a leak from the plastic heater core quick-connect hoses on the firewall. Due to its location, dripping coolant can run directly onto the cylinder 8 ignition coil and wire, causing it to short out and fail. A user on a Chevrolet forum confirmed this exact scenario fixed their P0308 after replacing ignition parts did not.
🎬 Watch: How to fix the common heater core connector leak.
• Intake Manifold Gasket Leak: A vacuum leak near the intake runner for cylinder 8 can lean out the air-fuel mixture and cause a misfire. This can be diagnosed by monitoring fuel trims with a scan tool or carefully spraying starter fluid around the intake manifold gasket with the engine running and listening for a change in idle speed.
• Low Cylinder Compression: Caused by internal mechanical issues like worn piston rings, a burnt valve, a broken valve spring, or a failing head gasket. This is less common than ignition or lifter issues but must be checked if other diagnostics fail. A compression test and/or a cylinder leak-down test is required to confirm.

Diagnosis Steps

1. Check if the Check Engine Light is solid or flashing. A flashing light indicates a severe misfire requiring immediate attention to prevent catalytic converter damage.
2. Use an OBD-II scanner to confirm P0308 and check for any other stored codes like P0300 or P050D.
3. Locate cylinder 8, which is the rearmost cylinder on the passenger side.
4. Carefully inspect the area around cylinder 8 for signs of a coolant leak from the heater hose connections on the firewall.
5. Perform an 'ignition swap test'. Swap the ignition coil from cylinder 8 with the coil from cylinder 6 (the next one forward on the same bank). Clear the codes and drive. If the code returns as P0306, the ignition coil is the faulty part.
6. If the code remains P0308, swap the spark plugs between the same two cylinders. If the code then moves to P0306, the spark plug was the issue. Inspect the old plug for wear, fouling, or damage.
7. If the code is still P0308, inspect the spark plug wire and the wiring harness for the coil and injector for damage, corrosion, or fluid contamination. Consider swapping the wire with another cylinder's.
8. If ignition components are good, test the fuel injector on cylinder 8 by listening for a click with a stethoscope or using a noid light to check for an electrical pulse.
9. If spark and fuel systems are confirmed to be working correctly, perform a compression test and a cylinder leak-down test on cylinder 8 to check for mechanical engine problems like bad rings, valves, or a head gasket leak.
10. If compression is good but the misfire persists, especially with a ticking noise, investigate the possibility of a worn camshaft or failed lifter, as noted in TSB #19-NA-219.

Parts You'll Likely Need

• Spark Plug (OEM #41-162 or 41-110) — This is the most common wear-and-tear item that causes a single-cylinder misfire. Part number may vary by specific year.
  Trusted brands: ACDelco, NGK

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or starting to affect other cylinders, a P0300 (Random/Multiple Cylinder Misfire) code may appear alongside P0308. This can sometimes point towards a systemic issue like a vacuum leak or a failing camshaft.
• P050D — This code for 'Cold Start Rough Idle' is sometimes seen with misfire codes. TSB #PIP5628G specifically links P050D with P0300-P0308 codes and requests diagnostic data be sent to GM's Technical Assistance Center (TAC).

Technical Service Bulletins (TSBs) & Recalls

• PIP5628G: Communicates a need for specific diagnostic information when diagnosing misfire codes P0300-P0308.
• PIP4138R: Advises checking for a worn camshaft lobe or lifter if standard diagnostics do not resolve P0300-P0308 misfire codes.
• PIP4819A: Recommends inspecting and replacing loose spark plug wires as a cause for P0300-P0308 codes.

Platform-Specific Known Issues

• AFM/DOD Lifter Failure: The Active Fuel Management (AFM) or Displacement on Demand (DOD) system lifters are a known major failure point. A collapsed or stuck lifter on cylinder 8 will cause a persistent misfire that cannot be fixed with ignition or fuel parts. This repair is labor-intensive and expensive.
• Worn Camshaft Lobe: TSB #PIP4138R directly links P0300-P0308 codes to worn camshaft lobes. This is a significant mechanical failure requiring camshaft and lifter replacement.

Mechanic-Grade Diagnostic Values

• Fuel Pressure (Key On, Engine Off) — expected: 55-65 psi. Failure: Pressure below this range indicates a weak fuel pump or leak.
• Fuel Pressure (at idle) — expected: 50-62 psi. Failure: Pressure below this range at idle can indicate a failing fuel pump or clogged filter.
• Ignition Coil Primary Resistance — expected: ~0.660 ohms. Failure: A significant deviation from this value suggests a faulty coil.
• Fuel Injector Coil Resistance — expected: 11-14 ohms. Failure: A reading outside this range, or a variance greater than 3 ohms between injectors, points to a failed injector.

Hidden / Shadow Codes Worth Checking

• Mode $06 Misfire Data: This is not a specific code but a data stream showing raw misfire counts for each cylinder, including cylinder 8. It can reveal misfires that are not yet frequent enough to set a P0308 code. (see via Accessible using a GM Tech2 or GDS2 scan tool, typically under Engine Data or Misfire Data menus. Some high-end aftermarket scanners may also display this data.)

Scan Tool Commands That Help

• GM Tech2 / GDS2: Misfire Graphic — To visually monitor misfire counts on all cylinders in real-time. This helps confirm if the misfire is isolated to cylinder 8 or if other cylinders are also misfiring intermittently.
• GM Tech2 / GDS2: Fuel Injector Balance Test — To command each injector to fire for a set duration and measure the corresponding drop in fuel pressure, identifying a weak or clogged injector on cylinder 8.
• GM Tech2 / GDS2: Reset Fuel Trims — After a repair that affects the air/fuel mixture (like fixing a vacuum leak or replacing an injector), this forces the PCM to relearn baseline fuel delivery values immediately.
• GM Tech2 / GDS2: Crankshaft Position Variation Learn (CASE Relearn) — This procedure must be performed after replacing the crankshaft position sensor, PCM, or flexplate to synchronize the sensor with the reluctor wheel. An incorrect learn value can cause false misfire detection.

Wiring & Ground Locations

• G103 — The main engine wiring harness ground, attached to the passenger side (right) cylinder head. Depending on the model year, it may be at the front or rear of the head.. This is a critical ground for the ECM. Corrosion or a loose connection at this point is a known cause of various misfire codes, including P0308, as it can disrupt sensor readings and ignition control signals.
• Engine Block to Firewall Strap — A braided ground strap connecting the rear of the engine block/cylinder head area to the firewall on the driver's side.. A poor connection here can cause a variety of electrical issues and introduce electrical noise into sensor signals, potentially leading to misfire detection.
• Cylinder 8 Injector/Coil Harness — The wiring that runs to the rearmost passenger side of the engine.. This section of the harness is susceptible to heat damage from the exhaust manifold and chafing against engine brackets. A short or open in the injector or ignition coil control wire will directly cause a P0308.

Real Owner Repair Stories

• Reddit user on r/ChevyTrucks (2011 Suburban (GMT900 platform, similar to Silverado)) — P0308 code.
  ❌ Tried (didn't work) Initial diagnosis pointed towards common ignition parts.
  ✅ What actually fixed it The user discovered the heater core quick-connects on the firewall were dripping coolant directly onto the #8 spark plug wire. Fixing the coolant leak and cleaning the wire resolved the P0308 code.
• Reddit user on r/MechanicAdvice (2015 Tahoe (K2XX platform, similar to Silverado)) — Intermittent misfire on cylinder 8 (P0308).
  ❌ Tried (didn't work) The misfire would come and go, making diagnosis difficult.
  ✅ What actually fixed it The wiring to the ignition coil for cylinder 8 was found to be pulling out of the connector, causing an intermittent loss of connection. Securing the wire in the connector fixed the issue.

When the Usual Fixes Don't Work

• In several documented cases, owners replaced spark plugs, wires, and ignition coils for cylinder 8 without resolving the P0308 code. The final fix was often an external factor, not a primary ignition or fuel component. One of the most notable examples is a leak from the heater core hose quick-connect fitting on the firewall, which drips coolant directly onto the cylinder 8 coil and wire, causing a short. Another confirmed fix was a corroded main ECM ground terminal (G103) on the passenger side cylinder head, which disrupted the ignition system's electrical signals. These instances highlight the importance of inspecting the surrounding environment and critical electrical grounds before assuming a new part has failed.

OEM Part Supersession History

• ACDelco 41-110 → ACDelco 41-162 — Supplier change and/or design update.
  Heads up: The 41-162 is physically shorter than the 41-110. While they are listed as interchangeable for many applications, some owners and mechanics report better idle quality and prefer to source the older 41-110 plugs, citing concerns about the manufacturing quality of the newer part number.

Model Year Variations Within This Range

• 2009-2010 vs 2010-2016: The engine transitioned from the LY6 to the L96 around 2010. The main difference is the L96 is Flex-Fuel capable, meaning it has different fuel injectors designed to handle E85. The LY6 is gasoline-only. Both are 6.0L V8s with VVT and without Active Fuel Management (AFM).
• 2009-2016: The location of the critical G103 ECM ground may vary. According to a GM document, it can be on the front or the rear of the right-side (passenger) cylinder head, depending on the specific model year.