P0307 on 2020-2021 GMC Sierra 1500: Cylinder 7 Misfire Causes and Fixes

What's Unique About the 2020-2021 Gmc SIERRA 1500

The 2020-2021 Sierra 1500's 5.3L L84 and 6.2L L87 V8 engines use a sophisticated system called Dynamic Fuel Management (DFM). This system can deactivate any number of cylinders to save fuel, but the special hydraulic valve lifters it uses are a well-documented failure point. These lifters can collapse or get stuck, preventing the valve from opening and causing a persistent misfire. An owner complaint for a 2020 model with a P0307 code described a "sudden loud pop" before the light came on, which is consistent with this type of mechanical failure. [ODI #11619484] This issue is so prevalent that multiple TSBs have been issued, and it affects a wide range of GM trucks and SUVs using the same engines.

Diagnostic Flowchart

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

Symptoms You May Notice

• Flashing or solid Check Engine Light
• Rough or shaking idle
• Noticeable loss of engine power
• Hesitation or stumbling during acceleration.
• Audible ticking, tapping, or popping noise from the engine bay, especially on a cold start.
🎬 Watch: How to tell if it's a lifter tick or exhaust leak.
• Reduced fuel economy
• Engine shaking under light throttle.

Most Likely Causes

1. Failed or Collapsed Valve Lifter 🔴 High Probability The Dynamic Fuel Management (DFM) system used in the L84 and L87 engines has lifters that are a known weak point. They can fail mechanically, often due to the internal locking pin, leading to a bent pushrod and a complete loss of valve function for that cylinder. GM has issued Technical Service Bulletin #23-NA-043 specifically addressing this internal lifter concern causing misfires. Failures have been reported at surprisingly low mileages. 🎬 See a breakdown of common lifter issues for L84 and L87 engines.
   How to confirm: Listen for a distinct ticking or tapping sound from the engine. A mechanic can perform a cylinder deactivation test with a scan tool or remove the valve cover to visually inspect the rocker arms and pushrods for lack of movement or damage while the engine is cranked. A collapsed lifter will be visibly compressible by hand once removed.
   Typical fix: Replacement of all valve lifters and guides on the affected cylinder bank, as per GM TSB 23-NA-043. If mileage is low (under 16,000 miles), GM recommends replacing lifters on both banks. The camshaft and pushrods must also be inspected for damage and replaced if necessary. This is a major engine repair requiring cylinder head removal.
   Est. part cost: $400-$1200
2. Faulty Ignition Coil 🟡 Medium Probability
   How to confirm: Swap the ignition coil from cylinder 7 with another cylinder (e.g., cylinder 1 or 3). Clear the codes and drive the vehicle. If the misfire code changes to the cylinder you moved the coil to (e.g., P0301 or P0303), the coil is bad.
   Typical fix: Replace the faulty ignition coil.
   Est. part cost: $40-$90
3. Worn or Fouled Spark Plug 🟡 Medium Probability
   How to confirm: Remove the spark plug from cylinder 7 and inspect it. Look for heavy carbon buildup, oil fouling, or a worn/damaged electrode. Compare it to a plug from a healthy 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: $8-$20 per plug
4. Clogged or Faulty Fuel Injector ⚪ Low Probability
   How to confirm: A professional can test the fuel injector's flow rate and electrical function using a scan tool or a dedicated injector tester. One can also listen for the injector's clicking sound with a mechanic's stethoscope to ensure it's operating. A resistance check can also be performed.
   Typical fix: Replace the faulty fuel injector. One owner on a forum reported fixing a P0307 by replacing the injectors and injector harness on the affected bank.
   Est. part cost: $70-$150

Rare But Worth Checking

• Bent Pushrod: This is almost always a direct consequence of a collapsed valve lifter, not a standalone failure. If a bent pushrod is found, the lifter must also be inspected and likely replaced.
• Damaged Camshaft Lobe: A failed lifter roller can score and damage the camshaft lobe, requiring camshaft replacement in addition to the lifters. This significantly increases the cost and complexity of the repair, with some owners opting for a full AFM/DFM delete kit that includes a new, non-DFM camshaft.
• Wiring Harness Issue: Damage or a poor connection in the wiring for the ignition coil or fuel injector for cylinder 7 can cause a misfire. This should be inspected before replacing more expensive components. Loose engine and body grounds are also a known issue.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0307 and check for any other pending or active codes.
2. If the Check Engine Light is flashing, stop the engine immediately to prevent catalytic converter damage.
3. Listen for any abnormal engine noises, such as a loud ticking or tapping, which would strongly suggest a valvetrain issue like a failed lifter.
4. Swap the ignition coil from cylinder 7 with another cylinder (e.g., cylinder 5). Clear the codes and see if the misfire moves to the new cylinder (P0305). If it does, the ignition coil is faulty.
5. If the misfire remains on cylinder 7, swap the spark plug from cylinder 7 with another cylinder. If the misfire follows the plug, the spark plug is the issue.
6. If the misfire persists on cylinder 7 after swapping the coil and plug, the problem is likely more serious and internal to the engine.
7. Inspect the wiring and connector for the cylinder 7 fuel injector and ignition coil for any visible damage or loose connections. Check engine ground straps, particularly G114 (engine harness) and the main block-to-chassis ground.
8. Given the high probability of lifter failure on these engines, the next step is professional diagnosis. A mechanic should remove the valve cover to inspect the valvetrain (rocker arms, pushrods) for proper movement while the engine is cranked. A rocker arm that isn't moving indicates a collapsed lifter or bent pushrod.
9. Refer to GM Technical Service Bulletin #23-NA-043, which directly addresses internal lifter concerns causing these misfire codes and provides repair guidelines based on vehicle mileage.
10. For 2020 models built between June and October 2020, consider the possibility of a broken valve spring as per GM bulletin PIP5752D. A cylinder leak-down test should be performed to confirm.

Parts You'll Likely Need

• Engine Valve Lifter (DFM) (OEM #12740071) — This is the most common major failure causing a P0307 code on this specific engine due to issues with the Dynamic Fuel Management (DFM) system. The repair typically involves replacing all lifters on the affected bank.
  Trusted brands: ACDelco (GM Genuine Parts)
  OEM price range: $40-$85 per lifter
  Aftermarket price range: $20-$40 per lifter
• Ignition Coil (OEM #12611424) — A failed ignition coil is a common cause for a single-cylinder misfire. It fails to provide the necessary spark to ignite the air-fuel mixture.
  Trusted brands: ACDelco, NGK, Denso
  OEM price range: $60-$90
  Aftermarket price range: $40-$70
• Spark Plug (OEM #12680072 (ACDelco Iridium)) — Spark plugs are a routine maintenance item and can become worn or fouled, leading to a weak or non-existent spark.
  Trusted brands: ACDelco, NGK
  OEM price range: $12-$20
  Aftermarket price range: $8-$15
• Camshaft (if damaged) (OEM #12723516 (For L84)) — If the roller on a failed lifter seizes, it can wipe out the corresponding lobe on the camshaft, requiring replacement.
  Trusted brands: ACDelco (GM Genuine Parts)
  OEM price range: $200-$350
  Aftermarket price range: $150-$250

Related Codes That Often Appear With This One

• P0300 — If the underlying issue, like a failing lifter, starts to affect other cylinders or if the computer is having trouble isolating the single misfire, a P0300 (Random/Multiple Cylinder Misfire) may be stored alongside P0307.
• P0420 / P0430 — These codes indicate 'Catalyst System Efficiency Below Threshold'. A persistent misfire from P0307 dumps unburned fuel into the exhaust, which can damage the catalytic converter and trigger these codes.
• P0106 / P0506 — A 'MAP Sensor Performance' code (P0106) or 'Idle RPM Lower Than Expected' code (P0506) may appear with a misfire if the cause is a significant mechanical failure, such as a broken valve spring, which disrupts engine vacuum and idle stability.

Technical Service Bulletins (TSBs) & Recalls

• TSB #23-NA-043: Titled 'Poor Engine Performance, Engine Misfires, Malfunction Indicator Lamp (MIL) Illuminated'. This is the primary document for this issue. It instructs technicians on how to diagnose and repair misfires caused by an 'internal lifter concern.' It specifies replacing lifters on one or both banks depending on vehicle mileage.
• TSB #19-NA-218: Titled 'Ticking Noise from the Engine'. This bulletin addresses customer complaints of a ticking noise on cold starts, which can be an early symptom of lifter failure. It diagnoses the cause as a lifter not having sufficient oil on startup.

Platform-Specific Known Issues

• Valve Lifter Failure: The most significant issue for the 2020-2021 Sierra V8s is the failure of the Dynamic Fuel Management (DFM) valve lifters. GM has issued TSB #23-NA-043 which details how an 'internal lifter concern' can cause misfire codes P0300 through P0308. The bulletin advises technicians to replace the lifters on the affected bank if a collapsed lifter or bent pushrod is found. This issue is widely discussed in owner forums, with many reporting failures at low mileage.
• Complete DFM Delete as a Permanent Fix: Due to repeat failures even after replacing lifters with new OEM parts, many owners and independent shops recommend a 'DFM delete'. This involves replacing all DFM lifters with standard (non-DFM) lifters, installing a non-DFM camshaft, and reprogramming the ECU to disable the system entirely. This is considered a permanent but expensive solution.

Mechanic-Grade Diagnostic Values

• Fuel Injector Coil Resistance — expected: 11-14 Ω. The difference between the highest and lowest reading across all injectors should be 3 Ω or less.. Failure: A reading outside the 11-14 Ω range or a variance greater than 3 Ω between injectors indicates a faulty injector.
• Low-Side Fuel Pressure (Key On, Engine Off) — expected: Approximately 55-65 psi.. Failure: Significantly lower pressure indicates a weak low-pressure fuel pump or a leak, which can starve the high-pressure pump.
• Fuel Injector Balance Test (via Scan Tool/AFIT) — expected: All cylinders should show a similar fuel pressure drop when the injector is pulsed.. Failure: An injector with a pressure drop variance of 10% or greater from the average indicates it is clogged or failing and should be replaced.

Hidden / Shadow Codes Worth Checking

• P0106 / P0506: While not 'hidden', these codes for MAP Sensor Performance (P0106) and Idle RPM Low (P0506) can appear alongside a P030x misfire code and may suggest a root cause of a significant mechanical failure, like a broken valve spring, rather than a simple ignition or fuel component failure. (see via Standard OBD-II scanner.)

Scan Tool Commands That Help

• GDS2 (GM Techline Connect): Fuel Injector Balance Test — Use this function after ruling out spark issues. It commands each injector to fire for a precise duration and measures the corresponding drop in fuel rail pressure to identify a weak or clogged injector without removing it from the engine.
• GDS2 (GM Techline Connect): Cylinder Deactivation / DFM System Test — To test the functionality of the DFM solenoids and lifters. This can help confirm if the valvetrain components are responding to commands from the ECM, which is critical when a collapsed DFM lifter is suspected.
• GDS2 (GM Techline Connect): Fuel Pump Relay Command — Used to manually turn on the low-pressure fuel pump to build pressure for static tests (KOEO) without starting the engine.

Wiring & Ground Locations

• G114 — Engine harness ground point.. GM issued an Engineering Information bulletin (PIE0548) regarding loose connections at this specific ground on 2019-2020 models, which can cause a wide range of electrical issues, including those that could manifest as a misfire.
• G110 — Body harness ground point.. Also mentioned in bulletin PIE0548 as a potential source of electrical problems due to a loose connection.
• Engine Block to Chassis Ground — A braided ground strap typically located on the passenger side, connecting the rear of the engine block to the vehicle's chassis/firewall. It is often difficult to see.. A poor connection at this primary ground can cause unstable sensor readings and intermittent electrical faults for the entire engine management system, leading to misfires.

OEM Part Supersession History

• 12645725, 12680871, 12698946 (and others) → 12740071 — Multiple revisions to the DFM (Dynamic Fuel Management) valve lifter design to improve durability and prevent collapse.
  Heads up: The long list of superseded part numbers (including 12569256, 12571595, 12619820, 12632143, 12639516) strongly indicates a history of design issues. Always use the latest available part number for replacement.

Model Year Variations Within This Range

• 2020: Vehicles built between June 1, 2020, and October 7, 2020, are subject to a service bulletin (PIP5752D) for potentially broken valve springs from a bad supplier batch. For a P0307 on a truck from this period, a broken valve spring is a distinct possibility that should be investigated before assuming lifter failure.
• 2020-2021: There were no significant hardware changes to the L84 engine's core components, sensors, or wiring between the 2020 and 2021 model years. The primary cause of lifter failure is consistent across both years.