P0308 on 2016-2022 GMC Sierra 1500: Cylinder 8 Misfire Causes & Fixes

What's Unique About the 2016-2022 Gmc SIERRA 1500

The 2016-2022 GMC Sierra 1500, with its 5.3L (L83/L84) and 6.2L (L86/L87) V8 engines, is unfortunately well-known for issues with its Active Fuel Management (AFM) or Dynamic Fuel Management (DFM) systems. These systems deactivate cylinders to save fuel but can lead to premature failure of the valve lifters. A collapsed or stuck lifter is a very common cause for a P0308 code on this specific platform, often turning what would be a simple ignition issue on other vehicles into a major mechanical repair requiring camshaft inspection or replacement. While cylinder 8 is not an AFM/DFM cylinder itself, failures of the system are systemic and can affect non-AFM cylinders, as reported by numerous owners.

Diagnostic Flowchart

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

Generation note: This range covers the end of the third generation (K2XX, 2016-2018) and the start of the fourth generation (T1XX, 2019-2022). Both generations use versions of the EcoTec3 V8 engine family. The K2XX models primarily use Active Fuel Management (AFM), while the T1XX models introduced the more advanced Dynamic Fuel Management (DFM). Both systems are linked to valve lifter failures that can cause this code. TSB 23-NA-043 specifically addresses lifter-related misfires on 2019-2021 models.

Symptoms You May Notice

• Rough or shaking idle.
• Hesitation or stumbling during acceleration.
• Noticeable loss of engine power.
• Solid or flashing Check Engine Light.
• Vehicle lurching during gear shifts. [ODI #11403994]
• A ticking, chirping, or squeaking noise from the engine, which may be more prominent on a cold start.
• Engine backfiring or popping sounds. [ODI #11659222]

Most Likely Causes

1. Failed or Fouled Spark Plug 🔴 High Probability Spark plugs are regular wear items. Cylinder 8 is notoriously difficult to access, tucked away at the back of the passenger side 🎬 Watch: How to tackle the nightmare cylinder 8 spark plug., and may be neglected during tune-ups. Some owners successfully change it without removing the fender liner, but it is a tight space.
   How to confirm: Remove the spark plug from cylinder 8 and inspect it for wear, carbon fouling, oil, or damage. Compare it to a plug from another cylinder. A bad plug is a very common fix.
   Typical fix: Replace the spark plug. It's best practice to replace all 8 plugs at the same time using plugs gapped to 0.040".
   Est. part cost: $5-$20 per plug
2. Faulty Ignition Coil or Spark Plug Wire 🔴 High Probability Heat and vibration can cause coils and wires to fail over time. A GM Technical Service Bulletin specifically mentions checking for loose spark plug wires as a cause for P030x codes. The wire connector can lose its retaining 'C' clip, causing a poor connection at the coil.
   How to confirm: Swap the ignition coil from cylinder 8 with another cylinder (e.g., cylinder 6). Clear the codes and drive. If the code changes to P0306, the coil is bad. Inspect the wire for damage or looseness at both ends.
   Typical fix: Replace the faulty ignition coil or spark plug wire set.
   Est. part cost: $40-$90 for a coil, $50-$100 for a wire set
3. Failed AFM/DFM Valve Lifter 🟡 Medium Probability This is a widely documented failure point on GM's EcoTec3 V8 engines. The complex lifters used for cylinder deactivation can become stuck, collapse internally, or have the roller bearing fail, which in turn damages the camshaft lobe. TSBs like 19-NA-219, 23-NA-043, and PIP5861 all address this issue directly.
   How to confirm: This is a difficult diagnosis. If ignition and fuel system checks pass, a distinct ticking noise is present, and other TSBs are referenced, a lifter is the likely cause. Professional diagnosis involves removing the valve cover to inspect for bent pushrods or lack of valve movement. One owner on the ScannerDanner forum reported a $6500 dealer repair for a collapsed lifter and camshaft on cylinder 8.
   Typical fix: Requires extensive engine work to replace all lifters and guides on the affected bank, and often the camshaft as well. Per TSB 23-NA-043, if the vehicle has under 16,000 miles, GM recommends replacing lifters on both banks. Many owners opt to install an AFM/DFM delete kit at this time.
   Est. part cost: $400-$1200+
4. Faulty Fuel Injector ⚪ Low Probability Injectors can become clogged or fail electronically. A Reddit user with a P0308 also had a P124F code, indicating an injector circuit short, possibly due to coolant leaking onto the wiring harness. Special Coverage Program N182202781 addresses faulty fuel injectors on some 2016-2017 models.
   How to confirm: Use a 'noid light' to check for an electrical pulse at the injector connector. You can also listen for a clicking sound from the injector with a mechanic's stethoscope. Swapping injectors between cylinders is a definitive but labor-intensive test.
   Typical fix: Replace the faulty fuel injector.
   Est. part cost: $50-$150

Rare But Worth Checking

• Worn Camshaft Lobe: Often occurs as a direct result of a failed lifter roller. If a lifter has failed, the camshaft should always be inspected for damage. TSB 19-NA-219 describes this as a potential cause for a P0300-P0308 misfire.
• Low Cylinder Compression: Could be caused by a bent valve, broken valve spring, worn piston rings, or a bad head gasket. A compression test is needed to verify. TSB 19-NA-219 also lists broken valve springs and sticking valves as potential causes.
• Leaking Valve Cover Gasket: Oil can leak from the valve cover gasket onto the spark plug and wire for cylinder 8, causing it to fail and trigger a misfire.
• Wiring Harness Chafing: A Reddit user mentioned that on some trucks, the engine wiring harness is known to rub against the front fender liner, which can cause wet-misfire issues. GM has issued TSB 21-NA-149 which details multiple wiring harness chafe points, including against the ECM/TCM bracket, upper control arm, and shock tower bolt.

Diagnosis Steps

1. Read the code with an OBD-II scanner and note any other codes present. Freeze frame data can show engine conditions when the misfire occurred.
2. Inspect the spark plug wire for cylinder 8. Ensure it is securely attached at both the coil and the spark plug. Per TSB #PIP5159C, check for a missing retaining 'C' clip on the wire end that connects to the coil.
3. Swap the ignition coil from cylinder 8 with another cylinder (e.g., cylinder 6). Clear the codes and drive. If the misfire code moves to the new cylinder (P0306), the ignition coil is faulty.
4. If the misfire remains on cylinder 8, remove and inspect the spark plug. Look for excessive wear, fouling, or damage. Replace if questionable, preferably as a full set.
🎬 Watch: Step-by-step guide to replacing all eight spark plugs.
5. If ignition components are good, inspect the fuel injector. Listen for a steady clicking sound. Check the wiring harness for damage, especially from coolant or oil leaks.
6. If the simple checks above do not reveal the cause, the issue is likely more serious. Listen for a distinct ticking or chirping sound from the engine, especially on a cold start, which could indicate a failed lifter.
🎬 See this walkthrough of a 5.3L misfire and engine tick.
7. Perform a cylinder compression test and a cylinder leak-down test. Low compression on cylinder 8 points to a mechanical problem like a bad valve, broken valve spring, worn piston rings, or head gasket.
8. If a lifter failure is suspected, professional service is highly recommended. Diagnosis involves removing the valve cover to check for bent pushrods and confirming valve movement. This repair often requires replacing the lifters, lifter guides, and camshaft.

Parts You'll Likely Need

• Spark Plug (OEM #12622561 (ACDelco 41-114) or 12680073 (ACDelco 41-166)) — This is the most common and simplest cause of a single-cylinder misfire. Cylinder 8 is hard to reach and can be overlooked. Part number may vary by specific year and engine.
  Trusted brands: ACDelco, NGK
  OEM price range: $10-$15
  Aftermarket price range: $5-$10
• Ignition Coil (OEM #12611424 (ACDelco D521C) or 12713673) — A common failure item that directly causes a misfire on a single cylinder. Part number may have been superseded.
  Trusted brands: ACDelco, Delphi
  OEM price range: $60-$90
  Aftermarket price range: $35-$60
• Valve Lifter Kit (AFM/DFM) — A very common major failure on this platform. A collapsed or stuck lifter is a primary cause of misfires that aren't resolved by ignition or fuel system repairs. The kit typically includes lifters and guides.
  Trusted brands: ACDelco, Sealed Power, Melling
  OEM price range: $300-$500
  Aftermarket price range: $200-$400

Related Codes That Often Appear With This One

• P0300 — If the condition causing the cylinder 8 misfire (like a failing fuel pump or major vacuum leak) begins to affect other cylinders, a P0300 Random Misfire code may appear as well. Many of the TSBs for lifter failure list P0300 along with the specific cylinder codes.
• P050D — A GM TSB links this code (Rough Idle During Cold Start) with misfire codes P0300-P0308, suggesting a related diagnostic path often pointing towards lifter issues.
• P124F — This code for 'Injector 8 Positive Voltage Control Circuit Shorted to Control Circuit' points directly to a problem with the fuel injector or its wiring on cylinder 8, providing a more specific diagnosis.

Technical Service Bulletins (TSBs) & Recalls

• 23-NA-043: Addresses misfires (P0300-P0308) caused by internal lifter concerns, providing guidelines for replacing lifters and guides based on mileage.
• 19-NA-219: Diagnostic guide for engine noises and misfires, pointing to causes like worn cam lobes, sticking valves, broken valve springs, and collapsed AFM lifters.
• PIP5861: Preliminary information about misfires resulting from a lifter that has come apart, recommending replacement of the lifter guide and all four lifters on the affected bank.
• PIP5159C: Instructs technicians to inspect for loose spark plug wires at the ignition coil, specifically looking for a missing 'C' clip on the wire end.
• 15-06-01-002M: Details diagnosis and correction for stuck/collapsed AFM lifters, bent pushrods, and camshaft damage.
• PIP5628G: Links rough idle codes (P050D) with misfire codes (P0300-P0308), aiding diagnosis.
• N182202781: A special coverage program (not a TSB) for faulty fuel injectors on certain 2016-2017 models in specific states.

Platform-Specific Known Issues

• AFM/DFM Lifter Failure: This is the most significant known issue. The failure can manifest as a collapsed lifter, bent pushrod, or a damaged roller that in turn destroys the camshaft lobe. TSB 23-NA-043 gives specific guidance on whether to replace lifters on one or both banks based on vehicle mileage.
• Spark Plug Wire Connection: TSB PIP5159C highlights a specific, simple-to-check issue where the spark plug wire comes loose from the ignition coil because of a missing or damaged 'C' clip inside the boot.
• Cylinder 8 Access: The location of cylinder 8 (rearmost on the passenger side) makes access for spark plug and wire replacement difficult, which can lead to these components being overlooked during maintenance.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Resistance — expected: 0.4 to 2 ohms. Failure: A reading of 0 ohms (short) or infinite/OL (open circuit).
• Ignition Coil Secondary Resistance — expected: 6,000 to 10,000 ohms. Failure: A reading significantly outside this range, or open/shorted.
• Fuel Injector Coil Resistance (Direct Injection) — expected: Approximately 12-15 ohms, with some sources citing around 13.5 ohms.. Failure: A reading significantly higher or lower than the other injectors, or open/shorted.
• Low-Pressure Fuel System (Key On, Engine Off) — expected: 55 to 62 PSI for the lift pump feeding the high-pressure pump.. Failure: Pressure below 55 PSI can indicate a weak in-tank fuel pump.
• High-Pressure Fuel System (Direct Injection) — expected: Can exceed 2,000 PSI, varies with engine load.. Failure: Requires a specialized scan tool to monitor; low readings under load can indicate a failing high-pressure fuel pump (HPFP).

Hidden / Shadow Codes Worth Checking

• Misfire Counter (Mode $06): Most advanced OBD-II scanners and dealer tools like the GDS2 can display misfire counts for each cylinder, even if they haven't reached the threshold to set a P0308 code. This is useful for confirming an intermittent misfire on cylinder 8. (see via Advanced OBD-II Scan Tool or GM GDS2 software. Look for 'Misfire History' or 'Misfire Graphic' data PIDs.)

Scan Tool Commands That Help

• GM GDS2 (or high-end aftermarket scanner): Cylinder Power Balance Test — This active test allows the technician to disable one cylinder at a time and observe the corresponding drop in engine RPM. If disabling cylinder 8 causes little or no change in RPM, it confirms that cylinder is not contributing power, pointing to a spark, fuel, or compression issue on that specific cylinder.
• GM GDS2 (or high-end aftermarket scanner): Fuel Injector Balance / Kill — After confirming a power loss on cylinder 8, this test can disable the fuel injector for that cylinder. If there is no change in engine operation, it suggests the injector was not working in the first place. This helps differentiate between a fuel and spark issue without disassembly.

Wiring & Ground Locations

• G110 / G114 — On the frame near the front of the vehicle, under the radiator support area on the driver's side.. GM issued Engineering Information (EI) bulletin PIE0548 regarding loose ground connections at G110 (Body Harness) and G114 (Engine Harness) on 2019-2020 models. A poor engine ground can cause a host of electrical issues, including weak spark or erratic sensor readings that can lead to misfire codes.
• Engine Harness Chafe Points (TSB 21-NA-149) — Multiple locations on 2019-2022 models, including: 1) against the ECM/TCM bracket, 2) the driver's side upper control arm, and 3) the shock tower bolt.. This TSB specifically addresses various drivability concerns caused by the engine harness rubbing through and shorting wires. A short in the ignition coil or fuel injector circuit for cylinder 8 due to this chafing can directly cause a P0308 code. The fix involves repairing the damaged wires and securing the harness with sleeves and zip ties.
• Engine to Firewall Ground Strap — Typically runs from the back of the cylinder head or engine block to the vehicle's firewall.. This strap ensures the engine block has a solid ground connection to the vehicle's body. Corrosion or a break in this strap can lead to intermittent and hard-to-diagnose electrical problems, including misfires.
• Underhood Fuse Block (Engine Wiring Harness Junction Block) — On the driver's side of the engine bay, near the fender.. This is the central hub for engine electronics. The circuits for the ignition coils and fuel injectors run through this block. Corrosion or a faulty internal relay within this block could potentially isolate a problem to a single cylinder circuit.

Real Owner Repair Stories

• ScannerDanner Forum (2016 GMC Sierra 5.3L) — Flashing check engine light with code P0308.
  ❌ Tried (didn't work) The story begins after the initial repair was already performed.
  ✅ What actually fixed it The dealership diagnosed a collapsed lifter on cylinder 8. The repair involved replacing the camshaft and all lifters, at a cost of $6,500 covered by an extended warranty. The code returned two days later, suggesting a potential secondary issue or misdiagnosis, but the primary confirmed fault was the collapsed lifter.
• Reddit r/gmcsierra (2018 Sierra 1500) — Misfire when cold and especially when raining/damp, code P0308.
  ❌ Tried (didn't work) Replacing all spark plugs., Replacing all spark plug wires (initially seemed to fix it, but the misfire returned after a 2-3 mile drive).
  ✅ What actually fixed it The owner's final update stated the fix was replacing the fuel injector for cylinder 8. The repair, including diagnostics, cost around $500.

OEM Part Supersession History

• Varies by year (e.g., 12570427 for 2007-2008) → Varies by year (e.g., 12642655 for 2009-2011) — To address issues with the PCV system design causing excessive oil consumption.
  Heads up: A TSB for older models notes that the left valve rocker arm cover was updated with a relocated PCV drain hole to prevent oil from entering the intake manifold. Using the wrong year's cover could cause an SES light due to different PCV orifice sizes. While this specific TSB is for older models, it highlights that valve cover designs can change and are not always interchangeable.

Model Year Variations Within This Range

• 2016-2018 (L83 Engine): These models primarily use Active Fuel Management (AFM), which deactivates 4 of the 8 cylinders (1, 7, 6, and 4) in a fixed pattern. Lifter failures are common on these specific cylinders but can cause issues system-wide.
• 2019-2022 (L84/L87 Engines): These models use the more advanced Dynamic Fuel Management (DFM), which has 17 different firing patterns and can run on as few as one cylinder. DFM uses special deactivating lifters on all 8 cylinders, making any cylinder susceptible to a DFM-related lifter failure. TSBs like 23-NA-043 are specific to these later models.
• 2014-2019 vs 2007-2014: The ignition coils used on 2014+ Gen V engines are a different design ('square' or 'boxy' style) compared to many earlier Gen IV LS engines which used a 'round' or 'cylinder-like' coil. They are not interchangeable.