P0301 on 2020-2025 Jeep Gladiator: Cylinder 1 Misfire Causes and Fixes

What's Unique About the 2020-2025 Jeep GLADIATOR

The 3.6L Pentastar V6 in the Gladiator is a workhorse engine used across many Jeep, Dodge, and Chrysler vehicles. For the Gladiator (JT), a P0301 code is typically a standard ignition issue. However, a unique challenge with this engine is the location of cylinder 1. It is on the driver's side bank (cylinders 1, 3, 5), which is tucked under the upper intake manifold. This makes accessing the coil and spark plug more labor-intensive than for the passenger-side cylinders (2, 4, 6), turning a simple part swap into a more involved job that requires removing the manifold.

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, sometimes only on cold starts
• Engine hesitation or stumbling during acceleration
• Noticeable loss of power, especially under load like climbing a hill
• Reduced fuel economy
• The Auto Start/Stop (ESS) system may become disabled and show a 'Not Ready' message
• Audible ticking noise from the engine bay, which could indicate a mechanical valvetrain issue
🎬 See what causes the Pentastar tick and how to fix it.

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Coil-on-plug systems are common failure points due to constant heat cycles and vibration. While generally reliable, a single coil failure is a frequent cause of isolated misfires on the Pentastar engine.
   How to confirm: Because cylinder 1 is hard to access, the easiest confirmation is often done after the intake manifold is already removed. Swap the ignition coil from cylinder 1 with another cylinder (e.g., cylinder 3 on the same bank, or cylinder 2 on the passenger side if you're willing to reassemble and disassemble again). Clear the codes and drive. If the code changes to P0303 or P0302, the coil is bad.
   Typical fix: Replace the faulty ignition coil. Since accessing cylinder 1 requires removing the intake manifold, many owners and technicians recommend replacing all three driver-side coils (1, 3, 5), all six spark plugs, and the intake gaskets at the same time to prevent future labor duplication.
   Est. part cost: $50-$110
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug Spark plugs are a regular maintenance item. TSB 09-013-20 REV. A was issued for some 2021 Gladiators/Wranglers built between Sept. and Nov. 2020 due to a manufacturing issue causing internal cracks in the original spark plugs, leading to misfires. Even without a defect, plugs wear out.
   How to confirm: After ruling out the coil, visually inspect the spark plug for wear, carbon buildup, oil fouling, or physical damage like a cracked insulator. A fouled plug is a strong indicator of the problem.
   Typical fix: Replace the spark plug. Given the labor to access cylinder 1, it is highly recommended to replace all six spark plugs at the same time if they are near the end of their 100,000-mile service interval.
   Est. part cost: $15-$30
3. Faulty Fuel Injector 🟡 Medium Probability → Shop Fuel Injector Injectors can become clogged with fuel deposits or fail electronically, preventing the correct amount of fuel from reaching the cylinder and causing a lean misfire.
   How to confirm: With the engine running, use a mechanic's stethoscope to listen to the injector; it should have a consistent, audible clicking sound. You can also test the electrical signal with a 'noid light'. This must be done after removing the intake manifold to access the driver's side fuel rail. A resistance test can also be performed; a good injector will read around 12-13 ohms.
   Typical fix: Replace the faulty fuel injector. This also requires removing the intake manifold and fuel rail.
   Est. part cost: $70-$150
4. Leaking Intake Manifold Gasket ⚪ Low Probability → Shop Engine Intake Manifold The gaskets sealing the upper and lower intake manifold can degrade or be installed improperly, causing a vacuum leak near a specific cylinder. This introduces unmetered air, leading to a lean condition and a misfire.
   How to confirm: With the engine running, carefully spray brake cleaner or a propane torch (unlit) around the intake manifold gaskets near cylinder 1. If the engine RPM surges or stumbles, a leak is present. This is difficult to do accurately on the driver's side before disassembly.
   Typical fix: Replace the upper and lower intake manifold gaskets. This is required maintenance anytime the intake manifold is removed to access a coil, plug, or injector on the driver's side bank.
   Est. part cost: $40-$80

Rare But Worth Checking

• Rocker Arm / Lifter Failure: → Shop Engine Rocker Arm The 3.6L Pentastar engine is known for a 'Pentastar Tick' which is often caused by the needle bearings in a rocker arm failing. This causes the arm to wear against the camshaft lobe, reducing valve lift and leading to a misfire. One owner on a forum had a P0300/P0301 that ended up being rocker arms needing replacement. If you hear a persistent ticking noise along with your P0301, this is a strong possibility and requires tearing down the top end of the engine to fix.
• Engine Mechanical Failure: In a forum discussion on JeepGladiatorForum.com, one owner with a persistent P0301 and associated ESS issues ultimately discovered the cause was coolant leaking into the cylinder through a flaw in the cylinder wall, which required a complete engine replacement under warranty. This is an extreme and rare case but highlights the need for a proper compression test if ignition and fuel issues are ruled out.
• PCM Software Issue: Emissions Recall Y68 was issued for some 2020 Gladiators because the PCM software might not enable misfire detection under certain conditions. While this wouldn't cause a misfire, it could prevent the code from being set correctly. TSB 18-061-24 also addresses various misfire codes with a PCM software update for some 2022 models. TSB 18-003-23 notes that on some models, misfires may only be detected when in 4WD-LO, also requiring a software update.

Diagnosis Steps

1. Confirm the code P0301 with an OBD-II scanner. 🎬 Watch a quick guide on diagnosing and fixing P0301 codes. Note any other codes and the freeze-frame data.
2. Identify cylinder 1. On the 3.6L Pentastar in a RWD configuration like the Gladiator, the passenger side bank (front to back) is cylinders 2, 4, 6. The driver's side bank is 1, 3, 5. Cylinder 1 is the front-most cylinder on the driver's side.
3. Listen for a ticking noise. A distinct, rhythmic tick from the driver's side valve cover area could point to a rocker arm issue, which is a more serious repair.
4. Because cylinder 1 is under the intake manifold, diagnosis requires disassembly. Plan to remove the upper intake manifold to access the ignition coil and spark plug for cylinder 1. A user on Reddit noted difficulty sliding the manifold off due to studs getting caught, requiring finesse.
5. Once the manifold is off, inspect the ignition coil and its wiring connector for damage or oil saturation.
6. Swap the cylinder 1 coil with the cylinder 3 coil (on the same bank). Reassemble everything with new intake gaskets, clear codes, and run the engine. If the code changes to P0303, the coil is the culprit.
7. If the code remains P0301, the next step is to inspect and replace the spark plug for cylinder 1. It is highly recommended to replace all six plugs and the intake gaskets at this time to save on future labor.
8. If the misfire persists, investigate the fuel injector for cylinder 1. Check its wiring and listen for operation before deciding to replace it. Test the injector's resistance with a multimeter; it should be between 12 and 14 ohms.
9. If ignition and fuel components are confirmed good, perform a compression test on cylinder 1 to rule out mechanical engine problems like bad rings or a bad valve. Note that a good compression test does not completely rule out rocker arm failure.
10. If a coolant leak is suspected, use a borescope to visually inspect inside the cylinder for coolant after a cooling system pressure test.

Parts You'll Likely Need

• Ignition Coil (OEM #68223569AD) — This is the most common failure part for a single-cylinder misfire. Replacing it typically resolves the P0301 code.
  Trusted brands: Mopar, Bosch, Delphi, NGK, Denso
  OEM price range: $90-$120
  Aftermarket price range: $30-$70
• Spark Plug (OEM #SP225755AB) — Spark plugs are a maintenance item and the second most likely cause. A worn or fouled plug cannot create a strong enough spark. TSB 09-013-20 REV. A also identified faulty original plugs on some 2021 models.
  Trusted brands: Mopar, Champion, NGK, Denso
  OEM price range: $20-$35
  Aftermarket price range: $10-$25
• Upper and Lower Intake Manifold Gaskets — These must be replaced anytime the intake manifold is removed for service on the driver's side bank of cylinders to prevent vacuum leaks.
  Trusted brands: Mopar, Fel-Pro, Mahle
  OEM price range: $60-$90
  Aftermarket price range: $30-$60

Related Codes That Often Appear With This One

• P0300 — If the condition causing the misfire is not isolated to one cylinder (e.g., a large vacuum leak, fuel pressure issue, or a systemic problem like failing rocker arms), a P0300 (Random/Multiple Cylinder Misfire) code may appear alongside P0301.
• P0303, P0305 — If there is a systemic issue on the driver's side bank, such as a leaking intake gasket affecting multiple cylinders, you may see misfire codes for other cylinders on that same bank (1, 3, 5).
• P0420 — Code P0420 (Catalyst System Efficiency Below Threshold) often appears with a persistent misfire because unburnt fuel is overheating and damaging the catalytic converter. This is a sign that the misfire needs to be addressed immediately.

Technical Service Bulletins (TSBs) & Recalls

• 09-011-25: General TSB listing various misfire codes including P0301 for 2025 models.
• 18-061-24: Addresses P0301 and other misfire/fuel pressure codes on 2022 models with the 3.0L Diesel, fixed with a PCM software update.
• 18-002-22 REV. A: Also lists P0301 among other codes in a TSB for 2021 models, related to various system improvements via software.
• 09-013-20 REV. A: Specifically addresses misfire codes (P0301-P0306) on 2021 Gladiators/Wranglers due to internally cracked OEM spark plugs from a specific manufacturing period. The prescribed fix is to replace all six spark plugs.

Platform-Specific Known Issues

• Access Difficulty: The primary issue for a P0301 on the Gladiator is that cylinder 1 is on the driver's side bank, requiring the removal of the upper intake manifold for access. This adds 2-3 hours of labor to what would otherwise be a 15-minute job, significantly increasing the repair cost and complexity.
• Rocker Arm Failure ('Pentastar Tick'): → Shop Engine Rocker Arm The 3.6L Pentastar has a known weakness in the valvetrain where rocker arm bearings can fail, causing a ticking noise and eventually a misfire. If P0301 is accompanied by a persistent tick, this is a likely cause and a much more involved repair than a simple coil or plug.
• Faulty OEM Spark Plugs: → Shop Spark Plug TSB 09-013-20 REV. A was issued for 2021 Gladiators and Wranglers built in late 2020 due to a batch of defective spark plugs that could crack internally and cause misfires. The fix is to replace all six plugs.

Mechanic-Grade Diagnostic Values

• Fuel Injector Resistance — expected: 12 - 14 ohms. Failure: A reading significantly higher or lower (e.g., an open circuit or a dead short) indicates a failed injector.
• In-Cylinder Pressure Waveform Analysis — expected: A consistent and uniform waveform pattern compared to healthy cylinders.. Failure: An abnormal waveform, such as one showing a loss of pressure during the compression stroke, can indicate a mechanical issue like a worn camshaft lobe from a failed rocker arm, even if a static compression test is normal.

Hidden / Shadow Codes Worth Checking

• Misfire Counter (Live Data PID): This is not a DTC, but a live data parameter (PID) that can be monitored with a capable scan tool. It shows the real-time count of misfire events per cylinder long before they reach the threshold to trigger a P0301 code. A technician can watch this counter increment on cylinder 1 during a test drive to confirm the misfire. (see via A professional scan tool like FCA's wiTECH or advanced consumer tools like AlphaOBD or JScan.)

Scan Tool Commands That Help

• Oscilloscope with Pressure Transducer: In-Cylinder Waveform Analysis — Use this advanced test when ignition and fuel system components have been ruled out, but a mechanical issue like a worn camshaft lobe or valvetrain problem is suspected. It provides a dynamic view of cylinder compression and breathing, which is more revealing than a static compression test for issues like a failed rocker arm.

Wiring & Ground Locations

• Cylinder 1 Injector Control Pin — On the Powertrain Control Module (PCM) connector. A pinout diagram shows this is often a Light Green wire responsible for the No. 1 injector signal.. If the injector itself tests good, a wiring issue between the PCM and the injector could be the cause. A continuity or voltage test at this pin can verify the integrity of the circuit.
• Engine and Chassis Grounds — Key locations include main grounds near the battery, on the frame behind the front passenger wheel, in the passenger kick panel, and above the spare tire.. A poor ground connection can cause erratic behavior in the ignition and fuel systems. While it would typically cause multiple, random issues, it's a foundational check. Verifying grounds are clean and tight is a crucial step in any electrical diagnosis.

Real Owner Repair Stories

• MyG37 Forum User (2011 Infiniti G37x (different vehicle, but identical diagnosis path for this failure type)) — P0301 Cylinder 1 Misfire, Service Engine Soon light.
  ❌ Tried (didn't work) Initial diagnosis focused on standard ignition/fuel causes.
  ✅ What actually fixed it The mechanic removed the spark plug and noted it was fouled and smelled of coolant. A borescope was inserted into the cylinder while the cooling system was pressure-tested, revealing a stream of coolant leaking onto the piston. The root cause was a head gasket failure, requiring major engine repair.
• JL/JT Wrangler/Gladiator Forums (Jeep Wrangler/Gladiator with 3.6L Pentastar) — Persistent ticking noise from the engine ('Pentastar Tick'), followed by a misfire code like P0301, often at higher RPMs initially.
  ❌ Tried (didn't work) Replacing spark plugs, Swapping ignition coils
  ✅ What actually fixed it The root cause was a failed rocker arm bearing, which seized and caused the camshaft lobe to wear down. This reduced valve lift, leading to a mechanical misfire. The fix required replacing the affected camshaft, all rocker arms, and lifters on that bank.

"I Checked Everything" — The Actual Cause

• Internal Coolant Leak: A standard smoke test checks for vacuum leaks and will come back clean. However, if the spark plug for cylinder 1 is fouled and smells sweet (like coolant), the actual cause may be a failed head gasket or a crack in the cylinder head/wall. This allows coolant to enter the combustion chamber, fouling the spark and causing the misfire. It can only be confirmed by pressure testing the cooling system and using a borescope to look for coolant inside the cylinder.

When the Usual Fixes Don't Work

• While rocker arm failure is a common cause of mechanical misfires on the 3.6L Pentastar, it is not a guaranteed diagnosis. One owner on a forum reported replacing all the rocker arms in response to an intermittent misfire, only for the problem to continue. This indicates that even if a common 'deep' mechanical fault is suspected and repaired, the true issue could be even more significant, such as a valve seating problem within the cylinder head itself, requiring a valve job or head replacement to finally resolve the misfire.

OEM Part Supersession History

• 68223569AB, 68223569AC → 68223569AD — Standard part revision and improvement by the manufacturer.
  Heads up: The newer part number is a direct replacement for the older versions.

Model Year Variations Within This Range

• 2021: Per TSB 09-013-20 REV. A, models built between September 1, 2020, and September 30, 2020, may have been equipped with a batch of faulty spark plugs prone to internal cracks, causing misfires. The recommended fix is to replace all six spark plugs.
• 2022: TSB 18-061-24 was issued to address various misfire codes, including P0301, with a PCM software update for some 2022 models.
• 2020-2025: TSB 18-003-23 notes a specific condition where misfire codes may only set when the vehicle is operated in 4WD-LO. This issue is resolved with a PCM software update.