P0306 on 2010-2017 GMC Yukon XL: Cylinder 6 Misfire Causes and Fixes

What's Unique About the 2010-2017 Gmc YUKON XL

The V8 engines in this generation of GMC Yukon XL (5.3L and 6.2L) are equipped with Active Fuel Management (AFM). This system deactivates cylinders—including cylinder 6—to improve fuel economy. Unfortunately, the hydraulic lifters used for this system are a known, widespread failure point. A collapsed or stuck AFM lifter on cylinder 6 is a very common cause for a persistent P0306 code, often accompanied by a distinct ticking noise from the engine 🎬 Watch: Hear what a failing AFM lifter sounds like and sometimes a bent pushrod.

Diagnostic Flowchart

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

Generation note: The 2010-2017 year range covers two generations of the GMC Yukon XL: the end of the third generation (2010-2014, GMT900 platform) and the beginning of the fourth generation (2015-2017, K2XX platform). Both generations use V8 engines with Active Fuel Management (AFM) and are susceptible to the same common causes for P0306, particularly ignition components and AFM lifter failure, which is the subject of multiple class-action lawsuits.

Symptoms You May Notice

• Rough idle or engine vibration
• Flashing or solid Check Engine Light
• Noticeable loss of engine power and sluggish acceleration
• Hesitation or stumbling when accelerating
• Engine ticking or clicking noise, especially if a lifter is the cause
• Service StabiliTrak / Traction Control warning lights may appear along with the misfire

Most Likely Causes

1. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug Spark plugs are a regular maintenance item. GM recommends replacement at 100,000 miles for the original equipment iridium plugs, but they can fail sooner.
   How to confirm: Remove the spark plug from cylinder 6 (third cylinder from the front on the passenger side) and inspect it for wear, carbon buildup, oil fouling, or a cracked insulator.
   Typical fix: Replace the spark plug. It is best practice to replace all 8 spark plugs at the same time for even performance. Use the correct OEM plug, such as an ACDelco 41-162 (for many 2010-2014 models) or 41-110.
   Est. part cost: $8-$25 per plug
2. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Heat and vibration can cause the coil-on-plug units to fail over time, leading to a weak or non-existent spark.
   How to confirm: Swap the ignition coil from cylinder 6 with another cylinder (e.g., cylinder 4, second on the passenger side). Clear the codes and drive. If the code changes to P0304, the ignition coil is bad.
   Typical fix: Replace the failed ignition coil. The OEM part is often an ACDelco D521C or similar.
   Est. part cost: $40-$90
3. Bad Spark Plug Wire 🟡 Medium Probability → Shop Spark Plug As cited in GM's Technical Service Bulletin #PIP4819A, spark plug wires can become loose at the coil or plug, or the wire itself can be damaged, causing misfires. [PASS 1 TSB, 2]
   How to confirm: Visually inspect the wire for cylinder 6 for damage, white marks from arcing, or looseness at the coil and spark plug. Ensure it is securely clicked into place at both ends. A resistance test should show between 4,000-20,000 ohms; a reading over 30,000 ohms indicates a bad wire.
   Typical fix: Replace the spark plug wire. It's often recommended to replace the full set.
   Est. part cost: $50-$100 for a set
4. Failed Active Fuel Management (AFM) Lifter 🟡 Medium Probability → Shop Engine Valve Lifter The AFM system deactivates cylinders 1, 4, 6, and 7. The special lifters for these cylinders are a notorious weak point and are prone to collapsing or getting stuck, causing a permanent misfire. This issue is so widespread it has led to multiple class-action lawsuits against GM.
   How to confirm: This is a more complex diagnosis. If ignition and fuel system checks don't resolve the misfire on cylinder 6, and there is a persistent ticking noise, an AFM lifter is the likely culprit. A compression test may show low or zero compression on cylinder 6. In some cases, removing the valve cover will reveal a rocker arm that is not moving because the lifter has collapsed, often resulting in a bent pushrod.
   Typical fix: This is a major repair that involves removing the cylinder head to replace the failed lifter(s), lifter guides, and often the camshaft if it was damaged by the failed lifter. Many owners and shops opt to perform an 'AFM delete' at this time, replacing the AFM components with standard lifters and disabling the system in the ECU 🎬 Watch: How AFM lifters fail and how the delete works to prevent recurrence.
   Est. part cost: $400-$1500 for parts, depending on whether an AFM delete is performed and if the camshaft needs replacement.
5. Clogged or Failed Fuel Injector ⚪ Low Probability → Shop Fuel Injector
   How to confirm: Listen for a clicking sound from the injector to confirm it's activating. A more definitive test is to swap the cylinder 6 injector with another cylinder (if accessible) and see if the misfire code follows. A professional scan tool can run an 'Injector Balance Test'.
   Typical fix: Replace the faulty fuel injector.
   Est. part cost: $50-$150

Rare But Worth Checking

• Intake Manifold Gasket Leak: → Shop Engine Intake Manifold A vacuum leak near the cylinder 6 runner can lean out the air/fuel mixture and cause a misfire. A smoke test is the most effective way to find such a leak.
• Low Engine Compression: Beyond a failed lifter, low compression can be caused by worn piston rings, a bad valve, or a blown head gasket. A cylinder leak-down test can pinpoint the source of the compression loss.
• Bent Pushrod: → Shop Engine Push Rod Often a direct consequence of a collapsed AFM lifter. When the lifter fails, it creates excessive slack in the valvetrain, and the pushrod can bend. A visual inspection after removing the valve cover will confirm this.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0306 and check for any other 🎬 See this video for a walkthrough of P0306 causes and fixes stored codes.
2. Note if the Check Engine Light is flashing. If so, avoid driving the vehicle to prevent catalytic converter damage.
3. Locate cylinder 6. On GM V8s, this is the third cylinder from the front on the passenger (right) side of the engine.
4. Inspect the spark plug wire for cylinder 6. Ensure it's securely connected and not damaged, per TSB #PIP4819A.
5. Swap the ignition coil from cylinder 6 to another cylinder (e.g., cylinder 4). Clear the codes and see if the misfire moves to P0304. If it does, the coil is faulty.
6. If the misfire remains on cylinder 6, remove and inspect the spark plug. Look for wear, fouling, or a cracked insulator. Replace if in doubt.
7. Listen for a persistent ticking/clicking sound from the passenger side of the engine. This is a strong indicator of a potential AFM lifter failure.
8. If basic steps fail, perform a compression test on cylinder 6. A reading of zero or very low pressure points to a mechanical issue like a stuck valve or, most commonly, a failed AFM lifter.
9. If compression is good but the misfire persists, consider testing the fuel injector by swapping it with another cylinder.

Parts You'll Likely Need

• Ignition Coil (OEM #ACDelco D521C (Verify application)) — This is a very common failure item that directly causes a single-cylinder misfire.
  Trusted brands: ACDelco, Delphi, NGK
  OEM price range: $70-$100
  Aftermarket price range: $40-$70
• Spark Plug (OEM #ACDelco 41-162 or 41-110 (Verify application)) — Spark plugs are a routine maintenance part and a frequent cause of misfires.
  Trusted brands: ACDelco, NGK
  OEM price range: $15-$25
  Aftermarket price range: $8-$15
• Spark Plug Wire Set — GM TSB #PIP4819A specifically calls out loose or faulty spark plug wires as a cause for this code.
  Trusted brands: ACDelco, NGK
  OEM price range: $80-$120
  Aftermarket price range: $50-$80
• AFM Valve Lifter (OEM #GM 12648846 (Verify application)) — A failed AFM lifter is a well-documented, common, and serious cause of P0306 on this platform.
  Trusted brands: ACDelco, General Motors
  OEM price range: $30-$50 per lifter
  Aftermarket price range: $20-$40 per lifter

Related Codes That Often Appear With This One

• P0300 — If the underlying issue (like a failing fuel pump or systemic AFM problem) becomes more severe, it can cause random misfires across multiple cylinders, triggering P0300.
• P0301, P0304, P0307 — These codes, along with P0306, correspond to the cylinders that are deactivated by the AFM system (1, 4, 6, 7). Seeing multiple misfires on these specific cylinders is a strong indicator of a systemic AFM problem, potentially involving the Valve Lifter Oil Manifold (VLOM) or multiple failed lifters.

Technical Service Bulletins (TSBs) & Recalls

• Bulletin #PIP4819A: Mentions that engine misfire codes (P0300-P0308) can be caused by loose or damaged spark plug wires. Recommends inspection and replacement.
• Bulletin #PIP5163A: While not a direct cause, this TSB discusses diagnosing engine misfires or oil consumption suspected to be from cylinder bore damage, which can be a consequence of other failures.
• Bulletin #PIP5493C: Addresses misfire DTCs on various GM engines and provides diagnostic direction, including checking AFM rocker arms if misfires are isolated to one bank.

Platform-Specific Known Issues

• Active Fuel Management (AFM) lifter failure is a significant and widely documented problem on the 5.3L and 6.2L V8 engines used in these vehicles. The lifters for cylinders 1, 4, 6, and 7 are prone to failure, leading to misfire codes for those specific cylinders. This issue has resulted in numerous class-action lawsuits against GM, alleging the components are defective. Failure often requires cylinder head removal and can also damage the camshaft, leading to a very expensive repair.

Mechanic-Grade Diagnostic Values

• Fuel Pressure (Key On, Engine Off) — expected: 50-60 PSI (345-414 kPa). Failure: Pressure significantly below 50 PSI can indicate a weak fuel pump or a leak in the fuel system.
• Fuel Injector Resistance — expected: 11 - 14 ohms. Failure: A reading outside this range indicates a faulty injector coil.
• Ignition Coil Primary Resistance — expected: 0.4 - 2.0 ohms. Failure: A reading outside this range suggests a fault in the coil's primary winding.
• Ignition Coil Secondary Resistance — expected: 6,000 - 10,000 ohms. Failure: Significant deviation from this range suggests a fault in the coil's secondary winding.
• Spark Plug Wire Resistance — expected: 4,000 - 20,000 ohms. Failure: A reading above 30,000 ohms indicates excessive resistance and a bad wire.
• AFM VLOM Solenoid Resistance — expected: 11 - 18 ohms. Failure: Readings significantly outside this range point to a faulty solenoid within the Valve Lifter Oil Manifold.
• Engine Compression — expected: 100 - 150 PSI and consistent across cylinders. Failure: Very low or zero compression on cylinder 6 points to a mechanical failure like a collapsed lifter, stuck valve, or worn piston rings.

Hidden / Shadow Codes Worth Checking

• Mode $06, TID $A2-$A7: Professional scan tools can access Mode $06 data, which contains raw misfire counts for each cylinder for the current and last ten driving cycles. This allows a technician to see the severity and frequency of the misfire on cylinder 6 (and others) before it's severe enough to keep the CEL on. (see via Use a professional scan tool (like a GM Tech 2, GDS2, or high-end Autel/Snap-on) that can display OBD-II Mode $06 test results.)

Scan Tool Commands That Help

• GDS2 / Tech2: Injector Balance / Active Fuel Injector Test (AFIT) — After ruling out spark issues, this command fires the cylinder 6 injector and measures the fuel pressure drop. If the drop is less than other cylinders, it confirms a clogged or failing injector.
• GDS2 / Tech2: Cylinder Deactivation / AFM Solenoid Test — This function allows the technician to command the AFM solenoids in the VLOM on and off to test their electrical integrity. It helps determine if a suspected AFM issue is caused by a bad solenoid, wiring, or a mechanical lifter.
• GDS2 / Tech2: Cancel Fuel Injectors — To isolate a mechanical noise. If a ticking sound persists after using this command to disable the cylinder 6 injector, it confirms the noise is mechanical (like a lifter) and not related to combustion.

Wiring & Ground Locations

• G102 — Typically located at the left rear of the engine; grounds all 8 ignition coils.. A poor connection at this ground point can cause weak or intermittent spark for all cylinders, potentially leading to misfire codes.
• G103 — Located on the cowl in the engine compartment, often above the brake booster. Another source places it on the front left of the engine block.. This is a critical ground for the ECM and Body Control Module (BCM). A faulty G103 ground can cause a wide range of erratic sensor readings and module behavior, potentially triggering false misfire codes.
• Engine Block to Firewall Straps — Braided ground straps connecting the engine block/cylinder heads to the vehicle's firewall.. These straps ensure the engine has a solid ground path to the chassis. Corrosion or a break can create electrical noise and interfere with sensor signals, including the crankshaft position sensor that detects misfires.

Real Owner Repair Stories

• YouTube channel 'Ford Boss Me' (2015 Chevy Tahoe PPV with 190,000 miles) — Flashing check engine light, P0306 code stored.
  ❌ Tried (didn't work) Swapped spark plug between cylinder 4 and 6, Swapped spark plug wire between cylinder 4 and 6, Installed a new ignition coil on cylinder 6
  ✅ What actually fixed it Diagnosis revealed a collapsed AFM lifter on the intake valve for cylinder 6. After removing the valve cover, the technician observed the rocker arm was loose and not moving, confirming the internal mechanical failure. The final fix required cylinder head removal to replace the lifters.

"I Checked Everything" — The Actual Cause

• In many instances on these GM V8s, a technician will find no vacuum leaks after a smoke test, confirm good spark and injector pulse, and even get an acceptable compression reading, yet the P0306 code persists. The actual cause is often a mechanically failed AFM lifter that is stuck or collapsed internally. This fault will not be revealed by smoke tests or basic electrical checks.

OEM Part Supersession History

• GM 12648846 (or similar older AFM lifters) → GM 12698946 (Newer DFM-style lifter) — GM redesigned the lifter for the newer Dynamic Fuel Management (DFM) system. This newer design is considered more robust against failure.
  Heads up: The newer DFM-style lifter (12698946) is backward-compatible and recommended for use in older AFM engines. However, the original AFM-only lifters must not be used in newer DFM engines.
• Original Valve Lifter Oil Manifold (VLOM) → GM 12571609 — GM released an updated VLOM to improve oil pressure regulation and flow to the AFM lifters, helping to address one of the root causes of lifter failure.

Model Year Variations Within This Range

• 2010-2014 (GMT900 Platform): These models use Gen IV V8 engines (e.g., 5.3L LC9/LMG, 6.2L L94) with Port Fuel Injection. Diagnosis for P0306 focuses primarily on ignition components, mechanical issues (AFM lifters), and port fuel injectors.
• 2015-2017 (K2XX Platform): These models use Gen V 'EcoTec3' V8 engines (e.g., 5.3L L83, 6.2L L86) with Direct Injection (DI). In addition to the common causes, diagnosis must also consider DI-specific issues like failing high-pressure fuel pumps and significant carbon buildup on intake valves, which can restrict airflow to cylinder 6 and cause a misfire.