P0303 on 2020-2025 Jeep Gladiator: Cylinder 3 Misfire Causes and Fixes

What's Unique About the 2020-2025 Jeep GLADIATOR

The 2020-2025 Gladiator primarily uses the 3.6L Pentastar V6 engine. For this engine, cylinder 3 is on the passenger side of the engine, in the middle position (front to back: 1-3-5). A key design aspect is that the entire upper intake manifold must be removed to access the ignition coils and spark plugs on this side of the engine (Bank 1). This makes the repair more time-consuming than for the driver's side cylinders (Bank 2), which are easily accessible.

Diagnostic Flowchart

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

Symptoms You May Notice

• Rough or shaky idle
• Engine stumbling or hesitating during acceleration
• Noticeable loss of engine power
• Check Engine Light is on and may be flashing
• Reduced fuel economy
• Smell of unburnt fuel from the exhaust
• Ticking or tapping noise from the top of the engine, which can point to a valvetrain issue.

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Coil-on-plug systems are common failure points on many modern engines as they age. Heat and vibration lead to eventual failure. A user on the Gladiator subreddit reported a P0303 accompanied by a P0353 (Ignition Coil C Malfunction), directly pointing to a coil failure 🎬 Watch: How to diagnose P0303 codes and test ignition coils. at only 13k miles.
   How to confirm: Swap the ignition coil from cylinder 3 with another cylinder (e.g., cylinder 1, the front-most on the same passenger bank). Clear the codes. If the misfire code changes to P0301, the coil is bad. This is the universally recommended first diagnostic step.
   Typical fix: Replace the faulty ignition coil. Since the intake manifold must be removed, it is highly recommended to replace all three coils (1, 3, 5) and the spark plugs on that bank at the same time to save on future labor.
   Est. part cost: $40-$100
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug
   How to confirm: After confirming the coil is good, swap the spark plug from cylinder 3 with another cylinder. If the misfire code follows the plug, the plug is bad. Visually inspect the plug for wear, oil, or carbon fouling. A cracked insulator is also a possibility.
   Typical fix: Replace the spark plug. It is best practice to replace all six spark plugs at the same time if they are near the end of their service life (typically around 100,000 miles for the OEM Iridium plugs, but failures can occur sooner). TSB #09-013-20 REV. A specifically notes that some 2021 Gladiators were built with defective spark plugs that could crack 🎬 Watch: Step-by-step walkthrough for changing spark plugs on this engine. internally and cause misfires, requiring the replacement of all six.
   Est. part cost: $10-$25 per plug
3. Faulty Fuel Injector 🟡 Medium Probability → Shop Fuel Injector
   How to confirm: Listen to the injector with a mechanic's stethoscope; it should have a consistent clicking sound. A more definitive test is to check the injector's resistance with a multimeter; an abnormal reading indicates failure. Swapping the injector with another cylinder is also an option, but it requires removing the fuel rail and is labor-intensive. A common resistance value for a good injector is around 12-12.5 ohms. 🎬 See this pro guide for troubleshooting Pentastar V6 misfires.
   Typical fix: Replace the faulty fuel injector. One owner on a Wrangler forum resolved their P0303 by replacing the injector after coil and plug swaps failed to fix the issue.
   Est. part cost: $50-$150
4. Leaking Intake Manifold Gaskets ⚪ Low Probability → Shop Engine Intake Manifold The gaskets are disturbed every time the coils/plugs on the passenger side bank are serviced. If they are not replaced or seated correctly, they can create a vacuum leak, leaning out the mixture for that bank and potentially causing a misfire.
   How to confirm: With the engine running, spray brake cleaner or a propane torch (unlit) around the intake manifold gasket area for cylinder 3. If the engine RPM changes, a leak is present.
   Typical fix: Replace the upper and lower intake manifold gaskets. This should be done whenever the intake manifold is removed for other service.
   Est. part cost: $30-$70 for a gasket set

Rare But Worth Checking

• Internal Engine Mechanical Issue (Rocker Arm/Camshaft Failure): The 3.6L Pentastar engine is known for potential valvetrain issues, where a rocker arm bearing fails, causing the roller to seize and damage the camshaft lobe. This typically presents as a persistent ticking noise from the engine that may be more noticeable on a cold start, followed by a misfire code like P0303. A forum member on JLWranglerForums described this exact scenario: a long-term ticking sound eventually led to a P0303 code, which required valvetrain repair. A compression test is the first step to diagnosing this.
• Blown Head Gasket / Cracked Cylinder Head: → Shop Engine Cylinder Head Though less common, a failed head gasket can cause coolant to leak into the cylinder, fouling the spark plug and causing a misfire. Symptoms include mysterious coolant loss, a sweet smell from the exhaust, or white smoke. One Gladiator owner on Reddit with a P0303 was diagnosed with a blown head gasket after moisture was found in the cylinder. Another on a Wrangler forum confirmed a P0303 was caused by a head gasket leak at 28k miles, which was identified by a leakdown test pushing coolant into the reservoir.

Diagnosis Steps

1. Confirm the P0303 code using an OBD-II scanner. Note if the Check Engine Light is flashing and if other codes like P0300 or P0353 are present.
2. Identify cylinder 3. On the Gladiator's 3.6L V6, it is the middle cylinder on the passenger side (Bank 1).
3. Listen for engine noises. A distinct 'ticking' from the passenger-side valve cover area could indicate a rocker arm/camshaft issue, which is a known problem.
4. Perform an ignition coil swap. This requires removing the upper intake manifold. Exchange the coil from cylinder 3 with the coil from cylinder 1. Clear the codes and drive the vehicle to see if the misfire code returns as P0301. If it does, the coil is the problem.
5. If the code remains P0303, perform a spark plug swap while the manifold is off. Exchange the spark plug from cylinder 3 with one from another cylinder. If the code follows the spark plug, the plug is faulty. Inspect the old plug for damage, wear, or fouling (oil/coolant).
6. If the misfire is still on cylinder 3, inspect the fuel injector. Listen for a steady clicking sound. Check the wiring harness for damage. An ohms test on the injector can confirm electrical integrity; a good injector should read around 12-12.5 ohms.
7. If ignition and fuel components seem okay, perform an engine compression test on cylinder 3. Low compression indicates a mechanical engine problem (e.g., valvetrain, head gasket, piston rings).
8. Inspect for vacuum leaks around the intake manifold, particularly near the cylinder 3 runner, especially if the gaskets were not replaced during a previous repair.

Parts You'll Likely Need

• Ignition Coil (OEM #68223569AD (supersedes 68223569AC, 68223569AB)) — This is the most frequent cause of a single-cylinder misfire. It's recommended to replace all three on the passenger bank at once due to the labor involved in removing the intake manifold.
  Trusted brands: Mopar, Delphi, NGK, Denso
  OEM price range: $50-$80
  Aftermarket price range: $40-$100
• Spark Plug (OEM #SP225755AB (replaces 68225755AA)) — Spark plugs are a routine maintenance item and a common cause of misfires. TSB 09-013-20 REV. A was issued for defective plugs on some 2021 models. They should be replaced along with the coils on the passenger side bank.
  Trusted brands: Mopar (OEM), NGK, Champion
  OEM price range: $15-$25
  Aftermarket price range: $8-$15
• Intake Manifold Gasket Set (OEM #68535427AA (Kit) or 05281823AA (Upper Gaskets)) — These gaskets must be replaced whenever the intake manifold is removed to prevent vacuum leaks. It is cheap insurance against having to do the job twice.
  Trusted brands: Mopar, Fel-Pro, Mahle
  OEM price range: $40-$70
  Aftermarket price range: $30-$60

Related Codes That Often Appear With This One

• P0300 — This code means 'Random/Multiple Cylinder Misfire.' It often appears with a specific cylinder misfire code like P0303 if the issue is severe or beginning to affect other cylinders. TSB 18-048-22 notes that if P0300 is present on a 2020 Gladiator, the right intake camshaft must be replaced along with a software update.
• P0301, P0305 — Misfires on other cylinders on the same bank (passenger side) can occur if the root cause is systemic, like a vacuum leak affecting the whole bank, or if multiple coils/plugs are failing around the same time. A user on the Jeep Gladiator Forum reported getting P0302 and P0303 together under hard acceleration.
• P0353 — This code for 'Ignition Coil C Primary/Secondary Circuit Malfunction' specifically points to an electrical fault in the cylinder 3 ignition coil circuit. A Gladiator owner reported this code along with P0303, confirming the coil was the problem.

Technical Service Bulletins (TSBs) & Recalls

• Bulletin #09-013-20 REV. A: Details a known manufacturing issue with spark plugs on some 2021 models that can cause internal cracks and lead to misfires (P0301-P0306). The fix is to replace all six spark plugs.
• Bulletin #18-002-22 REV. A: Lists P0303-00 'Cylinder 3 Misfire' as a potential code fixed by a PCM software update, however, this specific TSB applies to 2021 Gladiators with the 3.0L Diesel engine.
• Bulletin #18-048-22: For 2020 Gladiators, this TSB states that if a P0300 (Multiple Cylinder Misfire) is present, the right intake camshaft MUST be replaced along with a software update.
• Bulletin #09-011-25: Confirms P0303 as 'Cylinder 3 Misfire' for 2025 models.
• Bulletin #18-061-24: Lists P0303-00 'Cylinder 3 Misfire' among potential codes for 2022 models.

Platform-Specific Known Issues

• The primary issue for this code on the Gladiator is the labor involved. Accessing cylinder 3 requires removing the upper intake manifold, which adds significant time and complexity compared to cylinders on the driver's side.

Mechanic-Grade Diagnostic Values

• Fuel Injector Resistance — expected: 12.0 - 12.5 Ohms. Failure: A significantly higher reading (e.g., over 25 Ohms) or an open circuit (infinite resistance). One real-world case showed a faulty injector reading over 60 Ohms.
• Ignition Coil Primary Resistance — expected: 0.4 - 2.0 Ohms. Failure: A reading outside of the specified range indicates a faulty primary winding.
• Ignition Coil Secondary Resistance — expected: 6,000 - 10,000 Ohms. Failure: A reading outside of this range suggests a failure in the secondary winding.
• Fuel Pressure (System) — expected: Approximately 43.5 psi / 3 bar at the injector rail.. Failure: Low fuel pressure can cause lean conditions and misfires, though it would typically affect multiple cylinders.

Scan Tool Commands That Help

• wiTECH / wiTECH 2.0: ECU View - Actuators — The dealer-level tool can command individual injectors to fire or coils to spark, helping to isolate a component failure without physical swapping. It can also perform automated cylinder contribution tests.
• wiTECH / wiTECH 2.0: Module Reset / Calibration — After replacing certain components, such as a PCM or performing major engine work, this function is used to reset learned adaptations and ensure the new parts function correctly within the system.

Wiring & Ground Locations

• Main Engine Ground (G100 on similar models) — On the 3.6L engine block, often near the oil dipstick tube, connecting to the chassis. A similar setup shows a ground strap from the firewall to a stud on the rear coil pack bolt.. A poor engine ground can cause erratic behavior in all ignition and fuel components, leading to intermittent and hard-to-diagnose misfires.
• Main Battery Ground — A heavy gauge wire from the battery negative terminal to a stud on the passenger side inner fender, near the battery.. This is the primary ground for the entire vehicle's electrical system. Corrosion or looseness here can cause widespread issues, including misfires.
• Passenger Kick Panel Grounds — Inside the cabin, in the passenger-side kick panel area, there are typically multiple ground studs, sometimes with unused spots.. These grounds serve various interior and body control modules. While less likely to cause a single cylinder misfire, a fault here could affect PCM operation in rare cases.

Real Owner Repair Stories

• JL Wrangler Forums user (2018 Jeep Wrangler JL (shared 3.6L engine), 59k miles) — P0303 on cold startup, rough idle that clears quickly, minor coolant loss.
  ❌ Tried (didn't work) Spark plug swap and inspection.
  ✅ What actually fixed it Diagnosis confirmed a blown head gasket. A leakdown test on cylinder 3 caused the coolant level in the reservoir to rise. The recommended fix was to replace the head gasket, with a strong suggestion to replace the gasket on the other cylinder bank as well due to a pattern of failures.
• YouTube channel 'yellerlife' (2015 Jeep Wrangler JKU (shared 3.6L engine)) — P0303 code with audible engine misfire.
  ❌ Tried (didn't work) Swapped ignition coils; misfire did not move., Swapped spark plugs; misfire did not move.
  ✅ What actually fixed it An ohms test on the fuel injectors revealed the cylinder 3 injector had a resistance of ~65 ohms, while good injectors measured ~12 ohms. Replacing the faulty fuel injector resolved the misfire.

OEM Part Supersession History

• 68223569AB → 68223569AC, then 68223569AD — Standard part revision and improvement by the manufacturer over time.
  Heads up: The newer revisions (AC, AD) are direct replacements for the older part number and are fully compatible.

Model Year Variations Within This Range

• 2024-2025: For the 2024 model year, Jeep discontinued the 3.0L EcoDiesel engine option, making the 3.6L Pentastar V6 the sole powertrain. The 2024 refresh also included a new grille design, a standard 12.3-inch infotainment screen, and new wheel designs.