P0305 on 2018-2021 Chevrolet Suburban: Cylinder 5 Misfire Causes and Fixes

What's Unique About the 2018-2021 Chevrolet SUBURBAN

The 2018-2021 Suburban V8 engines (5.3L L83/L84 and 6.2L L86/L87) use an Active or Dynamic Fuel Management system (AFM/DFM) to improve fuel economy by deactivating cylinders. This system, while effective, has a known weakness: the specialized lifters can fail by collapsing, getting stuck, or having an internal pin break. This prevents the valve from operating correctly, leading to misfires. While standard ignition issues are still the most common cause, a P0305 code on this specific platform warrants a closer look at potential valvetrain and lifter problems, an issue highlighted in multiple manufacturer service bulletins.

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 Suburban generations. The 2018-2020 models belong to the 11th generation (K2XX platform), while the 2021 model marks the start of the 12th generation (GMT1XX). Both generations use similar Gen V V8 engines (5.3L and 6.2L) with fuel management systems (AFM/DFM) that are prone to lifter issues causing misfires. The 2019+ L84 5.3L engine uses DFM, which is a more advanced version of AFM.

Symptoms You May Notice

• Check Engine Light is on or flashing
• Rough or shaky idle
• Engine hesitation or stumbling during acceleration
• Reduced engine power
• Poor fuel economy
• A feeling like driving over a bump strip, sometimes mistaken for a transmission issue.
• Possible fuel smell from the exhaust.
• A distinct ticking, chirping, or squeaking noise from the engine bay, often associated with a failed lifter.

Most Likely Causes

1. Worn Spark Plug 🔴 High Probability
   How to confirm: Remove the spark plug from cylinder 5 and inspect it for wear, fouling, or damage. Compare it to a new plug or a plug from a known good cylinder.
   Typical fix: Replace the spark plug. It is recommended to replace all 8 spark plugs at the same time for even performance.
   Est. part cost: $5-$20 per plug
2. Faulty Ignition Coil 🔴 High Probability Coil-on-plug systems are a common failure point. Cracks in the housing or internal shorts can cause a lack of spark.
   How to confirm: Swap the ignition coil from cylinder 5 with another cylinder (e.g., cylinder 1). Clear the codes and drive the vehicle. If the code changes to P0301, the ignition coil is faulty.
   Typical fix: Replace the faulty ignition coil.
   Est. part cost: $40-$100
3. Bad Spark Plug Wire 🟡 Medium Probability Wires can become loose or damaged. Some aftermarket wires are too long and can rub against the steering shaft, causing damage and an intermittent connection.
   How to confirm: Inspect the wire for visible damage, corrosion, or a loose connection at the coil and spark plug. Ensure it is securely clicked into place on both ends. A loose wire is a common and simple fix.
   Typical fix: Replace the spark plug wire set. Ensure the new wire is routed correctly to avoid contact with the steering shaft.
   Est. part cost: $50-$120 for a set
4. Failed AFM/DFM Lifter 🟡 Medium Probability The Active/Dynamic Fuel Management systems on these GM V8s use special lifters that can become stuck, collapse due to a broken internal pin, or fail to pump up with oil. This is a well-documented issue across the GM truck and SUV lineup.
   How to confirm: After ruling out ignition and fuel issues, a distinct ticking noise is a strong indicator. 🎬 See how to identify failed lifter noise in this video. A compression test may show low compression on cylinder 5. Definitive diagnosis requires removing the valve cover to inspect for a bent pushrod or a lifter that is not moving with the camshaft.
   Typical fix: This is a complex repair. Per TSB 23-NA-043, GM's procedure depends on mileage. For a 2021 model under 16,000 miles, all lifters and guides on both banks should be replaced. Over 16,000 miles, only the affected bank needs replacement. The repair involves removing the cylinder head(s), 🎬 Watch this teardown to see how lifters are removed. replacing the faulty lifter(s), lifter guides, and often gaskets and head bolts. The camshaft should also be inspected for damage.
   Est. part cost: $300-$800+
5. Clogged or Faulty Fuel Injector ⚪ Low Probability
   How to confirm: Listen to the injector with a mechanic's stethoscope to ensure it's clicking. For a more definitive test, swap the injector with another cylinder (a more involved job) and see if the misfire code follows the injector.
   Typical fix: Replace the faulty fuel injector.
   Est. part cost: $70-$150

Rare But Worth Checking

• Intake Manifold Gasket Leak: A vacuum leak near the cylinder 5 intake runner can lean out the air/fuel mixture and cause a misfire. This is less common for a single-cylinder misfire but still possible.
• Low Compression (Valves, Piston Rings): Beyond a failed lifter, other mechanical issues like a burnt valve, broken valve spring, or worn piston rings can cause a loss of compression and a persistent misfire. A cylinder leakage test can help diagnose these issues.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0305 and check for any other codes. 🎬 Watch: Step-by-step guide to diagnosing a GM V8 misfire. Note if the check engine light is solid or flashing.
2. Perform a visual inspection. Look for loose connections on the cylinder 5 ignition coil and spark plug wire. Check for any obvious damage to the wiring.
3. Listen to the engine. A prominent ticking or tapping noise can point directly to a valvetrain issue like a collapsed lifter.
4. Swap the ignition coil from cylinder 5 with another cylinder (e.g., cylinder 1, which is front driver's side). Clear the codes, run the engine, and see if the misfire moves to P0301. If it does, the coil is bad.
5. If the misfire remains on cylinder 5, swap the spark plug wire with another cylinder and re-test. Check that the wire is not rubbing on the steering shaft.
6. If the misfire still remains on cylinder 5, remove and inspect the spark plug. Look for wear, oil fouling, or damage. Replace if necessary, even if it looks okay, as they are inexpensive.
7. If ignition components are good, the next step is to check the fuel injector. Swapping injectors is more complex and may require professional help.
8. If ignition and fuel systems are ruled out, perform a compression test on cylinder 5. Low compression points towards a mechanical issue.
9. If compression is low, the most likely cause on this engine is a failed AFM/DFM lifter. This diagnosis is confirmed by removing the valve cover to inspect the valvetrain for a collapsed lifter or bent pushrod.

Parts You'll Likely Need

• Ignition Coil (OEM #12674754 (superseded by 12726023)) — A common failure point for ignition systems, leading directly to a misfire in a single cylinder.
  Trusted brands: ACDelco, Delphi
  OEM price range: $60-$90
  Aftermarket price range: $40-$70
• Spark Plug (OEM #12622561 (ACDelco Iridium)) — Spark plugs are wear items and a fouled or worn plug is a primary cause of misfires.
  Trusted brands: ACDelco (Iridium), NGK
  OEM price range: $10-$20
  Aftermarket price range: $8-$15
• AFM/DFM Lifter Kit — A known mechanical weak point on these engines that directly causes misfire codes when they fail. Kits often include lifters, guides, and gaskets.
  Trusted brands: ACDelco, General Motors, Michigan Motorsports
  OEM price range: $300-$500 (for one bank)
  Aftermarket price range: $200-$400
• Valve Cover Gasket — Required to be replaced when removing the valve cover to inspect or replace lifters.
  Trusted brands: ACDelco, Fel-Pro
  OEM price range: $30-$50
  Aftermarket price range: $20-$40

Related Codes That Often Appear With This One

• P0300 — If the misfire is severe or intermittent, the ECM may log a P0300 (Random/Multiple Cylinder Misfire) in addition to the specific cylinder code. This is very common with failing AFM/DFM lifters.

Technical Service Bulletins (TSBs) & Recalls

• 23-NA-043: Addresses engine misfires (including P0305) on 2021 models due to internal lifter concerns. It provides guidelines for replacing lifters on one or both banks depending on vehicle mileage.
• 19-NA-219: Provides diagnostic advice for engine noises (chirp, squeak, tick) and misfires (P0300-P0308), listing potential causes like worn cam lobes, sticking valves, and collapsed AFM lifters.
• 19-NA-218: Addresses a cold-start engine tick noise that may be caused by a lifter not getting sufficient oil. This bulletin is referenced by TSB 23-NA-043 for vehicles outside the specific breakpoint window.
• PIP4819A: An older bulletin, but it highlights a recurring theme of checking for loose spark plug wires as a cause for misfires on GM V8 engines.

Platform-Specific Known Issues

• AFM/DFM Lifter Failure: The most significant issue for this platform. The complex lifters used for cylinder deactivation can fail, causing them to collapse or get stuck. This results in a misfire (often with a P0300 code) and can also damage the camshaft if not addressed. TSB 23-NA-043 directly addresses this concern for 2021 models, recommending lifter replacement to fix misfire codes including P0305. The failure can be a collapsed lifter, a stuck lifter, or a broken internal locking pin. A user on the Chevrolet Forum reported lifter failure at just 8,000 miles on their 2021 Suburban, and again at 84,000 miles.

Mechanic-Grade Diagnostic Values

• Low-Side Fuel Pressure (Key On, Engine Off) — expected: 55-62 PSI. Failure: Pressure below 55 PSI may indicate a weak fuel pump or a leak.
• Cylinder Power Balance RPM Drop — expected: A noticeable and consistent RPM drop (e.g., 100-150 RPM) when a cylinder is deactivated.. Failure: Little or no RPM drop when cylinder 5 is deactivated indicates it was not contributing power, confirming a misfire.

Hidden / Shadow Codes Worth Checking

• Mode 6 Misfire Counts: The Engine Control Module (ECM) tracks misfire events for each cylinder even before they reach the threshold to set a P030x code. A professional scan tool can access this 'Mode 6' data to see which cylinder is misfiring intermittently. (see via A professional-grade OBD-II scan tool with Mode 6 data capability.)

Scan Tool Commands That Help

• GDS2 (GM Dealer Scan Tool): Cylinder Power Balance Test — This is a primary diagnostic step after reading codes. It allows a technician to electronically disable the fuel injector or ignition to cylinder 5 and observe the RPM drop. If there is little to no drop compared to other cylinders, it confirms cylinder 5 is the source of the misfire without contributing power.
• GDS2 (GM Dealer Scan Tool): Misfire Counter — To monitor real-time misfire events on each cylinder during a test drive or at idle. This is crucial for diagnosing intermittent misfires that don't immediately set a hard code.

Wiring & Ground Locations

• G102 — Located at the left rear of the engine; it is the ground for all 8 ignition coils.. A loose or corroded G102 ground could cause weak or intermittent spark on multiple cylinders, including cylinder 5, leading to misfires that might be hard to trace to a single component.
• G103 / G104 — Located on the cylinder heads (G103 on the front of the passenger side head, G104 on the rear of the driver's side head for some models).. These are critical engine block grounds. A poor connection at these points can cause a host of electrical issues, including problems with the ECM and ignition system that could manifest as a misfire code.
• Cylinder 5 Ignition Coil Connector — On the driver's side valve cover, third coil from the front.. This is the direct electrical connection for the coil. Technicians test for 12V+ on the power feed wire (typically pink on GM vehicles) with the key on, and check the ground connection. A damaged connector or wire at this point will cause a P0305.

Real Owner Repair Stories

• Reddit user in r/ChevyTrucks (2019 Silverado 1500 5.3L V8 with 78k miles) — Check Engine Light with Service ESC and ABS warnings, sluggish engine, and rough shifting.
  ❌ Tried (didn't work) Oil change, Lucas Oil fuel additive, Checking spark plug gap
  ✅ What actually fixed it Dealer service found a compression issue due to stuck/failed lifters. The fix was to replace all 16 lifters and the camshaft, which was covered under the powertrain warranty.
• Chevrolet Forum user (2021 Suburban High Country 6.2L L87) — Check engine light, lifter/camshaft issue diagnosed by dealer.
  ❌ Tried (didn't work) A previous dealer repair at 8,000 miles where all lifters were replaced.
  ✅ What actually fixed it The user reported a second lifter failure at 84,000 miles, requiring another lifter and camshaft replacement. This highlights the recurring nature of the issue for some owners.
• Reddit user in r/Silverado (2019 Silverado 1500 5.3L) — Lifter failure on cylinder 2.
  ❌ Tried (didn't work) Replacing only the affected bank of lifters.
  ✅ What actually fixed it Less than 100 miles after replacing one bank of lifters, a lifter on cylinder 8 failed. The final, correct repair required dropping the engine to replace the camshaft and all new lifters again, indicating that a partial repair can be insufficient.

OEM Part Supersession History

• 12674754 → 12726023 — Standard OEM part revision. GM often updates parts to improve reliability or address minor issues discovered in the field.
  Heads up: The new part number (12726023) is the correct direct replacement for the original. No incompatibility is noted.

Model Year Variations Within This Range

• 2019-2021: Starting in 2019 on the L84 5.3L and L87 6.2L engines, GM replaced Active Fuel Management (AFM) with the more advanced Dynamic Fuel Management (DFM). AFM deactivates four specific cylinders, while DFM can deactivate any number of cylinders in 17 different patterns. This means all 8 cylinders on DFM engines have deactivation-style lifters, whereas only 4 cylinders did on AFM engines, theoretically increasing the potential points of failure.