P0303 on 2018-2025 Chrysler Pacifica: Cylinder 3 Misfire Causes & Fixes

What's Unique About the 2018-2025 Chrysler PACIFICA

While a P0303 code on many vehicles points to a simple ignition component, on the 2018-2025 Pacifica with the 3.6L Pentastar V6, it warrants a more serious investigation. This engine platform has a documented history of cylinder head and valvetrain issues that can manifest as a persistent cylinder 3 misfire. NHTSA owner complaints for this specific vehicle repeatedly link the P0303 code to severe problems like warped cylinder heads, blown head gaskets, and failed valve guides, making it crucial to rule out these major repairs before settling on a simple fix. Cylinder 3 is located on the rear bank of the engine against the firewall, making it more labor-intensive 🎬 Watch: How to access and replace rear bank plugs and coils. to access than cylinders on the front bank.

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
• Engine sputtering, running rough, or shaking, especially at idle or on a cold start.
• Loss of power and hesitation during acceleration.
• Distinct ticking or tapping noise from the engine top end (the 'Pentastar Tick'), which may get louder with RPM.
• Excessive white exhaust smoke and coolant loss, indicating coolant is being burned.
• Decreased fuel economy.
• Engine stalling intermittently.

Most Likely Causes

1. Failed Ignition Coil 🔴 High Probability Coil-on-plug systems are common failure points on many modern engines. The 3.6L Pentastar is known to be sensitive to ignition component quality.
   How to confirm: Swap the ignition coil from cylinder 3 with another cylinder (e.g., cylinder 1, which is on the same bank). Clear the codes and drive. If the misfire code changes to P0301, the coil is faulty.
   Typical fix: Replace the failed ignition coil. It is often recommended to replace all coils on the same bank, especially if they are original and high-mileage.
   Est. part cost: $30-$70 per coil
2. Worn or Fouled Spark Plug 🔴 High Probability
   How to confirm: Remove the spark plug from cylinder 3 and inspect it for wear, carbon buildup, or fouling from oil or coolant. A coolant-fouled plug (white, crystalline deposits) points to a head gasket leak. A plug that is wet with fuel could indicate an ignition or compression problem.
   Typical fix: Replace the spark plug. It is best practice to replace all six spark plugs at the same time. Due to the labor involved in removing the intake manifold for the rear bank, replacing all three rear plugs (1, 3, 5) at once is highly recommended.
   Est. part cost: $10-$25 per plug
3. Cylinder Head or Head Gasket Failure 🟡 Medium Probability The 3.6L Pentastar engine has a history of cylinder head issues, particularly in earlier years, though problems persist. NHTSA complaints for the Pacifica specifically cite warped cylinder heads and blown head gaskets as a cause for P0303. Coolant leaking into the cylinder is a common symptom, often causing a misfire on cold starts.
   How to confirm: Perform a cylinder leak-down test and a cooling system pressure test. Bubbles in the coolant reservoir during the test or a loss of pressure in the cooling system are strong indicators. A borescope inspection may reveal a 'steam-cleaned' piston top or visible coolant in the cylinder.
   Typical fix: This is a major repair requiring replacement of the cylinder head gasket and potentially machining or replacing the cylinder head itself. The timing cover must be removed to access a timing chain guide bolt for head removal.
   Est. part cost: $400-$1500 for head gasket set and/or new cylinder head
4. Failed Valvetrain Components (Rocker Arms, Lifters) 🟡 Medium Probability The Pentastar engine is known for issues with rocker arm bearings failing, which causes the roller to seize and wear down the camshaft lobe. This is often preceded by a distinct ticking noise. NHTSA complaints confirm this can cause a P0303, citing stuck intake valves and dropped valve guides.
   How to confirm: This requires removing the valve cover for a visual inspection of the rocker arms, camshaft lobes, and lifters for cylinder 3. Check for loose rocker arms or visible scoring on the camshaft lobes.
   Typical fix: Replace all 12 rocker arms on the affected bank (or all 24) and any damaged lifters or camshafts. It is considered best practice to replace all of them to prevent future failures.
   Est. part cost: $150-$500 for a full set of rocker arms and lifters
5. Clogged or Failed Fuel Injector ⚪ Low Probability
   How to confirm: Swap the fuel injector from cylinder 3 with another cylinder. If the misfire code follows the injector, it is the cause. This is more labor-intensive than swapping a coil as it requires removing the fuel rail. A multimeter can also be used to check the injector's resistance; a good injector should read around 12 ohms.
   Typical fix: Replace the faulty fuel injector.
   Est. part cost: $50-$120

Rare But Worth Checking

• Low Engine Compression: Beyond a head gasket, this can be caused by worn piston rings or a damaged valve. A compression test will confirm this. A leak-down test can further pinpoint the source of the leak (rings, intake valve, or exhaust valve).
• Wiring Harness Damage: Rodents can chew through the wiring for the ignition coil or fuel injector, causing an electrical fault that triggers the misfire code. A visual inspection of the harness leading to cylinder 3 is recommended.
• Powertrain Control Module (PCM) Failure: In very rare cases, the driver circuit within the PCM that controls the ignition coil or fuel injector for cylinder 3 can fail. This is typically diagnosed only after all other possibilities have been exhausted.

Diagnosis Steps

1. Read the fault codes with an OBD-II scanner to confirm P0303 and check for any other codes (e.g., P0300, P105C).
2. Note the freeze frame data to see the engine conditions (temperature, RPM) when the code was set. A misfire on a cold start (low engine temp, short run time) often points to a head gasket leak allowing coolant to seep in overnight.
3. Listen for a distinct ticking noise from the engine, which is a strong indicator of rocker arm/lifter failure.
4. Visually inspect the wiring and connector for the cylinder 3 ignition coil and fuel injector for any damage.
5. Swap the ignition coil from cylinder 3 to a different cylinder on the same bank (e.g., cylinder 1). Clear codes and run the engine. If the code changes to P0301, the coil is bad.
6. If the misfire stays on cylinder 3, remove and inspect the spark plug. A plug fouled with coolant (white/ashy) is a strong sign of a head gasket leak.
7. If ignition components are good, perform a dry and wet compression test on cylinder 3. A significant loss of compression indicates a mechanical fault.
8. Perform a cylinder leak-down test to pinpoint the source of the leak (rings, intake valve, or exhaust valve).
9. If compression and leak-down tests are good, remove the valve cover to inspect the camshaft lobes and rocker arms for cylinder 3 for scoring or excessive wear.
10. If all else fails, test the fuel injector by checking its resistance or swapping it with another cylinder.

Parts You'll Likely Need

• Ignition Coil (OEM #68223569AD) — This is one of the most common and easiest to replace causes of a single-cylinder misfire.
  Trusted brands: Mopar, NGK, Delphi
  OEM price range: $50-$80
  Aftermarket price range: $30-$60
• Spark Plug (OEM #SP225755AA (Champion Iridium)) — Spark plugs are a routine maintenance item and can cause misfires when worn or fouled. Accessing the rear bank is labor-intensive, so replacing all is wise.
  Trusted brands: Champion, NGK
  OEM price range: $15-$25
  Aftermarket price range: $8-$15
• Cylinder Head Gasket Set (OEM #Varies by year, e.g., 68157224AC) — Required for a head gasket failure, a known issue on this platform causing coolant leaks into the cylinder.
  Trusted brands: Mopar, Fel-Pro
  OEM price range: $200-$350
  Aftermarket price range: $100-$200
• Rocker Arm & Lifter Kit (OEM #Varies, e.g., 5184296AH (Rocker Arm)) — The failure of rocker arm bearings is a very common cause of misfires and ticking noises on the 3.6L Pentastar engine.
  Trusted brands: Mopar, Melling
  OEM price range: $20-$30 per rocker arm
  Aftermarket price range: $150-$250 for a full engine kit

Related Codes That Often Appear With This One

• P0300 — Random Misfire. This may appear alongside P0303 if the underlying issue, such as a vacuum leak, failing valvetrain components on one bank, or a head gasket leak, begins to affect other cylinders.
• P105C — Intake Valve Stuck in Low Lift Position. This manufacturer-specific code, when seen with P0303, strongly points to a mechanical valvetrain problem in cylinder 3, as noted in NHTSA complaint #11611534.
• P0456 — EVAP System Small Leak. While not directly related to the misfire cause, a PCM software update (TSB 18-001-19 REV. B) was issued to address several false codes, including P0456, on 2018 Pacificas. This TSB will not fix a mechanical misfire but ensures the PCM software is current.
• P219A — Bank 1 Air-Fuel Ratio Imbalance. Since cylinder 3 is on Bank 1, a persistent misfire can disrupt the oxygen sensor's readings for that entire bank, leading to this code.

Technical Service Bulletins (TSBs) & Recalls

• 18-001-19 REV. B: A PCM software update released May 1, 2019, for 2018 models to address several erroneously set DTCs, including P0456 (EVAP leak), and improve idle quality. It is not a direct fix for a mechanical misfire but is recommended to ensure the vehicle's software is up to date.

Platform-Specific Known Issues

• On the transversely mounted 3.6L Pentastar in the Pacifica, the cylinders are numbered 1-3-5 on the bank against the firewall (Bank 1) and 2-4-6 on the front bank (Bank 2). Cylinder 3 is the middle cylinder on the difficult-to-access rear bank, which requires removal of the upper intake manifold for service.
• This is the common term for the audible ticking/tapping sound caused by failing rocker arm roller bearings. The sound is a primary symptom that often precedes or accompanies a misfire code like P0303. The failure of the bearing causes the arm to have excessive play or seize, damaging the camshaft lobe.

Mechanic-Grade Diagnostic Values

• Fuel Injector Resistance — expected: 12.0 - 12.5 Ohms. Failure: A significantly higher reading (e.g., 63 Ohms) or an open/short circuit indicates a failed injector. Readings slightly out of spec (e.g., 11.4 Ohms) may also indicate a problem.
• Ignition Coil Primary Resistance — expected: ~0.46 Ohms. Failure: A reading outside of the manufacturer's specification.
• Ignition Coil Secondary Resistance — expected: 9.5 - 15.70 kOhms. Failure: A reading outside of this range suggests a faulty coil winding.
• Fuel Rail Bolt Torque — expected: 4 ft-lbs (5.4 Nm). Failure: N/A - This is an installation specification.
• Ignition Coil Bolt Torque — expected: 71 in-lbs (8 Nm). Failure: N/A - This is an installation specification.

Scan Tool Commands That Help

• wiTECH (Dealer Tool): OBD II Monitors -> 'Which cylinder is misfiring' — To view live misfire counts for each individual cylinder, which is essential for diagnosing intermittent misfires or confirming the specific cylinder at fault when a P0300 (random misfire) is also present.
• High-Level Aftermarket Scan Tool: Power Balance Test / Cylinder Drop Test — To actively disable individual cylinders (one at a time) via the scan tool to see which cylinder causes the least change in engine RPM and sound. If disabling cylinder 3 causes no change, it confirms that cylinder was not contributing, pinpointing the misfire.

Wiring & Ground Locations

• Cylinder 3 Injector Connector — On the rear bank of the engine (against the firewall), middle injector. The connector has a red sliding lock tab.. This is the electrical connection for the cylinder 3 fuel injector. The two pins can be used to test injector resistance. The PCM grounds this circuit to fire the injector.
• Engine Block Ground Strap — There are multiple grounds. One key ground goes from the engine block/manifold area to the chassis. On older Pacificas, a key ground was located near the transmission stud (G101).. A poor engine ground can cause a weak spark or erratic sensor readings, potentially leading to misfire codes. While not a primary cause for a single-cylinder misfire, it should be checked if multiple electrical issues are present.

Real Owner Repair Stories

• Reddit user in r/ChryslerPacifica (2018 Chrysler Pacifica Touring L, 88,000 miles) — Intermittent stalling, rough start, followed by a solid check engine light for P0303.
  ❌ Tried (didn't work) The user was preparing for a head gasket diagnosis under warranty.
  ✅ What actually fixed it Another user in the same thread reported fixing their P0303 on a 2018 model at 105,000 miles by replacing all spark plugs and coil packs, showing it can sometimes be a standard ignition issue.
• YouTube video by a mechanic (2017 Chrysler Pacifica, 103,000 miles) — P0302 (Cylinder 2 misfire, but same bank and issue as P0303), heavy engine steam, empty coolant reservoir.
  ❌ Tried (didn't work) Replacing spark plugs and ignition coil did not resolve the misfire.
  ✅ What actually fixed it Diagnosis confirmed coolant in the cylinder via borescope. The ultimate fix was replacing the cylinder head gasket. The video confirms that to do this job on the rear bank, the timing cover must be removed.
• Reddit user in r/ChryslerPacifica (2019 Chrysler Pacifica) — Head gasket leak diagnosis from a shop.
  ❌ Tried (didn't work) N/A
  ✅ What actually fixed it The user was quoted $6,600 for a head gasket replacement. Other users in the thread confirmed this is a known, expensive issue, with some suggesting a complete engine replacement from a company like Jasper might be more cost-effective than just a head gasket repair due to the risk of a warped block.

OEM Part Supersession History

• 5184296AD, 5184296AE, 5184296AF, 5184296AG → 5184296AH — This is the Mopar part number for the valve rocker arm, a frequent failure point in the Pentastar valvetrain that leads to ticking and misfires. The multiple supersessions indicate revisions to address the original design's flaws.
• 68223569AC → 68223569AD — This is the Mopar part number for the ignition coil. Part numbers are often updated for minor manufacturing changes or supplier shifts.

Model Year Variations Within This Range

• 2021-2025: The Pacifica received a major facelift for the 2021 model year, including revised styling and a new Uconnect 5 infotainment system. While the core 3.6L Pentastar V6 engine remained, some vehicles use the 'ERC' engine code variant which has different heads and cams compared to the older 'ERB' code and specifies 0W-20 oil. This may affect internal engine parts compatibility.
• 2018: A specific Technical Service Bulletin (TSB 18-001-19 REV. B) was released for 2018 models to update the PCM software. This update addresses several potential false codes, including P0456 (EVAP leak), and can improve idle quality and Engine Start-Stop (ESS) performance. While it won't fix a mechanical P0303, ensuring the PCM is updated is a good first step.