P0308 on 2008-2015 Chevrolet Silverado 1500: Cylinder 8 Misfire Causes & Fixes

What's Unique About the 2008-2015 Chevrolet SILVERADO 1500

While cylinder 8 itself is not an AFM (Active Fuel Management) cylinder, the V8 engines in this era of Silverado (both GMT900 and K2XX) are notorious for issues with their AFM system. This system deactivates cylinders 1, 4, 6, and 7 to save fuel, but the specialized lifters are a common failure point. A collapsed AFM lifter can cause widespread oiling problems or valvetrain instability that could potentially contribute to issues in other cylinders. More directly, cylinder 8's location at the rear of the engine bay on the passenger side makes its ignition components susceptible to heat damage and leaks from nearby heater hoses.

Diagnostic Flowchart

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

Generation note: This range covers two Silverado generations: the GMT900 (2008-2013) and the K2XX (2014-2015). The GMT900 trucks use Vortec V8s, while the 2014-2015 K2XX trucks introduced the newer EcoTec3 V8 engine family. Both engine types have Active Fuel Management (AFM) and are susceptible to lifter failure, though components like spark plugs, coils, and fuel injectors differ between generations. For example, the 2014+ EcoTec3 engines use a direct injection fuel system, which can have unique failure modes like leaking injector seals causing compression loss.

Symptoms You May Notice

• Rough or shaking idle
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Flashing or solid Check Engine Light
• Reduced fuel economy
• Engine ticking or tapping noise, which could indicate a lifter issue
• Smell of fuel from the exhaust

Most Likely Causes

1. Worn or Fouled Spark Plug 🔴 High Probability Spark plugs are a regular maintenance item with a recommended 100,000-mile service interval that is often stretched, leading to wear. Cylinder 8 is at the back of the engine and can be harder to reach, sometimes getting skipped during maintenance.
   How to confirm: Remove the spark plug from cylinder 8 and inspect it for wear, carbon buildup, oil fouling, or damage. Compare it to a plug from a working cylinder.
   Typical fix: Replace the spark plug. It is recommended to replace all 8 spark plugs at the same time if they are near the end of their service life. Use ACDelco Iridium plugs for best performance.
   Est. part cost: $10-$25 per plug
2. Failed Ignition Coil 🔴 High Probability
   How to confirm: Swap the ignition coil from cylinder 8 with one from another cylinder (e.g., cylinder 6). Clear the codes and drive the truck. If the code changes to P0306, the coil is faulty.
   Typical fix: Replace the failed ignition coil. It's a simple, single-bolt removal.
   Est. part cost: $40-$100
3. Bad Spark Plug Wire 🟡 Medium Probability Wires degrade from heat and age. A coolant leak from heater core quick-connect hoses near the firewall is a known issue that can drip directly onto the #8 plug wire, causing it to fail and trigger a P0308.
   How to confirm: Inspect the wire for cracks, corrosion, signs of arcing, or moisture from a coolant leak. Test its resistance with a multimeter.
   Typical fix: Replace the spark plug wire. It's often sold in a set for all 8 cylinders.
   Est. part cost: $50-$150 for a set
4. Failed AFM/DFM Lifter or Other Valvetrain Issue 🟡 Medium Probability The Active Fuel Management (AFM) system lifters are a well-documented weak point on 5.3L and 6.2L GM V8s, prone to collapsing or getting stuck. While cylinder 8 is not an AFM cylinder, a failure in the system can lead to oil pressure problems or send debris through the engine, potentially affecting non-AFM lifters as well.
   How to confirm: Listen for a distinct ticking/tapping sound from the engine that increases with RPM. A compression test on cylinder 8 may show low readings. Diagnosis is often confirmed by removing the valve cover and observing rocker arm movement while the engine is running; a collapsed lifter will result in no movement.
   Typical fix: This is a major repair requiring removal of the cylinder head(s) to replace all lifters, lifter guides, and often the camshaft. Many owners opt for an 'AFM delete kit' to prevent future failures.
   Est. part cost: $500-$1500 for parts
5. Clogged or Faulty Fuel Injector ⚪ Low Probability
   How to confirm: Use a 'noid light' to confirm the injector is receiving an electrical pulse. You can also swap the injector with another cylinder to see if the misfire follows, though this is more labor-intensive, especially on direct-injection engines (2014+).
   Typical fix: Replace the faulty fuel injector. On 2014+ models with direct injection, the injector seals must also be replaced.
   Est. part cost: $50-$150

Rare But Worth Checking

• Intake Manifold Gasket Leak: A vacuum leak near the cylinder 8 runner can lean out the air/fuel mixture, causing a misfire. This can be diagnosed with a smoke test or by carefully spraying starting fluid near the intake runner and listening for a change in engine RPM.
• Low Compression: Caused by more severe mechanical issues like a worn piston ring, a bad valve, or a head gasket failure. A compression test is required for diagnosis. A healthy cylinder should typically have 120-150 PSI or more. On 2014+ models, a failed direct injection seal can also cause a loss of compression.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0308 and check for any other codes. Note freeze frame data if available.
2. Visually inspect the area around cylinder 8 (passenger side, rearmost cylinder). Look for obvious damage, loose connections, or coolant leaks from the heater hoses above the spark plug wire.
3. Swap the ignition coil from cylinder 8 with another cylinder (e.g., cylinder 6). Clear codes and drive. If the code changes to P0302, the coil is bad.
4. If the misfire remains on cylinder 8, swap the spark plug with another cylinder. If the code moves, the spark plug is bad.
5. Inspect and test the spark plug wire for cylinder 8. Check for physical damage and test resistance with a multimeter.
6. Listen carefully for a metallic ticking noise from the engine, which could indicate a valvetrain or lifter problem.
7. Perform a compression test on cylinder 8. A healthy reading should be above 120 PSI and consistent with other cylinders. Low compression points to an internal mechanical problem.
8. Test the fuel injector pulse with a noid light. If the pulse is present, consider having the injector professionally cleaned or tested.
9. If a ticking noise is present and compression is low, the next step is often removing the valve cover to inspect the valvetrain (rockers, pushrods, valve springs) for cylinder 8. This can confirm a collapsed lifter.
10. If all else fails, seek a professional diagnosis. They can perform more advanced tests like a cylinder leak-down test or use an oscilloscope to analyze sensor data.

Parts You'll Likely Need

• Spark Plug (OEM #ACDelco 41-162 (Iridium, supersedes 41-110)) — This is the most common failure point and a standard maintenance item. A worn plug cannot create a strong enough spark. The 41-162 is the updated Iridium plug recommended for these engines.
  Trusted brands: ACDelco, NGK
  OEM price range: $12-$20
  Aftermarket price range: $8-$15
• Ignition Coil (OEM #12699383 (ACDelco D521C is a common replacement)) — Ignition coils generate the high voltage for the spark plug and can fail from heat and age, causing a weak or no-spark condition.
  Trusted brands: ACDelco, Delphi
  OEM price range: $70-$100
  Aftermarket price range: $40-$70
• AFM Lifter Replacement Kit (OEM #12571595, 12619820 (individual lifter numbers)) — For persistent misfires accompanied by engine ticking, a failed Active Fuel Management (AFM) lifter is a very common cause on these specific engines. A complete kit is needed for the repair.
  Trusted brands: ACDelco, Delphi, Michigan Motorsports
  OEM price range: $400-$700
  Aftermarket price range: $250-$500
• Spark Plug Wires Set — The wire for cylinder 8 is prone to failure from heat and potential coolant leaks. It's best practice to replace them as a set if they are old.
  Trusted brands: ACDelco, NGK
  OEM price range: $80-$120
  Aftermarket price range: $50-$90

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or affects multiple cylinders, a P0300 (Random/Multiple Cylinder Misfire) may be stored alongside P0308.

Technical Service Bulletins (TSBs) & Recalls

• PIP5628G: A general bulletin requesting specific diagnostic information be sent to GM's Technical Assistance Center (TAC) for persistent misfire codes (P0300-P0308), indicating a known pattern of difficult-to-diagnose misfires.
• PIP5163H: Discusses engine misfires and ticking noises related to AFM lifters that may be collapsed or stuck. It notes that this will typically set a P0300 and misfires on cylinders 1, 4, 6, or 7.
• 15-06-01-002D: A bulletin related to engine oil consumption and AFM operation, which can be a contributing factor to lifter failure if oil levels are not maintained.

Platform-Specific Known Issues

• Active Fuel Management (AFM) Lifter Failure: The most significant known issue. The specialized lifters on cylinders 1, 4, 6, and 7 are prone to failure. While cylinder 8 is not an AFM cylinder, a collapsed lifter elsewhere can cause oil pressure loss or send metal debris through the engine, potentially damaging the lifter or camshaft lobe for cylinder 8.
• Heater Hose Coolant Leak: The plastic quick-connect fittings for the heater hoses at the firewall are a common failure point. They are located directly above the cylinder 8 spark plug and coil area. When they leak, coolant drips onto the spark plug wire and boot, causing corrosion and ignition failure that specifically triggers a P0308 code.
• Carbon Buildup on Intake Valves (2014+ EcoTec3): The 2014 and newer models with direct injection (EcoTec3) do not have fuel spraying on the back of the intake valves. This can lead to significant carbon buildup over time, which can restrict airflow or cause the valve to not seat properly, leading to a misfire.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Winding Resistance — expected: 0.4 - 2.0 Ohms. Failure: A reading outside this range (open or shorted) indicates a faulty coil.
• Ignition Coil Secondary Winding Resistance — expected: 6,000 - 11,100 Ohms (6.0kΩ - 11.1kΩ). Failure: A reading outside this range indicates a faulty coil winding.
• Fuel Pressure (Low Side - 2008-2013 Vortec) — expected: 55 - 62 PSI. Failure: Pressure below 55 PSI can indicate a weak fuel pump, which could contribute to a lean misfire under load.
• Fuel Pressure (High Side at Idle - 2014-2015 EcoTec3) — expected: 500 - 900 PSI. Failure: Significantly higher (e.g., 2500 PSI) or lower pressure at idle points to a problem with the high-pressure fuel pump (HPFP) or its sensor.
• Long Term Fuel Trims (LTFT) — expected: Within +/- 10% at idle and steady cruise.. Failure: Consistently high positive trims (e.g., +15% or more) on Bank 2 (which includes cylinder 8) can indicate a vacuum leak near cylinder 8. Consistently high negative trims can indicate a leaking injector.

Scan Tool Commands That Help

• GDS (Global Diagnostic System): Camshaft Position Actuator System Control — In cases of extended crank or crank-no-start along with misfire codes, this function can cycle the cam phaser solenoid. If a phaser is stuck, it can cause valve timing issues leading to misfires. This helps determine if the phaser is responsive.

Wiring & Ground Locations

• G103 — On the front of the passenger side (right side) cylinder head.. This is a primary ground for the Engine Control Module (ECM). A corroded or loose G103 can cause erratic sensor readings and difficult-to-diagnose misfires on all cylinders, including cylinder 8.
• G104 — On the rear of the driver's side (left side) cylinder head.. This is a primary engine-to-chassis ground strap. While not directly for cylinder 8, a poor connection here can cause the entire ignition system to have a weak ground path, potentially leading to weaker spark and intermittent misfires.
• Cylinder 8 Ignition Coil Connector — The electrical connector on the ignition coil for cylinder 8, located at the rearmost position on the passenger side valve cover.. The wiring harness to the #8 coil can become brittle from heat. There are reports of the wiring pulling out of the back of the connector, causing an intermittent connection and a P0308 code that comes and goes.

Real Owner Repair Stories

• 509VolleyballDad on r/ChevyTrucks (2011 Suburban (GMT900 platform, similar to Silverado)) — P0308 code.
  ❌ Tried (didn't work) Initially considered replacing all plugs and wires.
  ✅ What actually fixed it The heater core quick-connect hoses near the firewall were leaking coolant directly onto the #8 spark plug wire. Fixing the coolant leak and cleaning the plug wire resolved the P0308 code without replacing ignition parts.
• Vdubtuner86 on r/MechanicAdvice (2015 Tahoe (K2XX platform, similar to Silverado)) — Intermittent misfire on cylinder 8 (P0308).
  ❌ Tried (didn't work) Initial diagnosis was difficult as the misfire would come and go.
  ✅ What actually fixed it The wiring to the ignition coil on cylinder 8 was pulling out of the connector, causing an intermittent open circuit. Securing the wire in the connector fixed the problem.

Model Year Variations Within This Range

• 2014-2015: The introduction of the EcoTec3 engine family brought Direct Injection (DI). This makes the fuel system more complex, with both a low-pressure in-tank pump and a high-pressure mechanical pump on the engine. A P0308 on these models could be related to a failing high-pressure pump or, more commonly, carbon buildup on the intake valves, which is not an issue on the port-injected 2008-2013 Vortec engines.
• 2008-2013: These models use the Vortec engine family with port fuel injection. Their fuel system diagnostics are simpler, focusing on a single in-tank fuel pump with a target pressure of 55-62 PSI. They are not susceptible to intake valve carbon buildup in the same way as the later direct-injection models.