P0304 on 2017-2025 Chrysler Pacifica: Cylinder 4 Misfire Causes and Fixes

What's Unique About the 2017-2025 Chrysler Pacifica

While any engine can have a bad spark plug, the 3.6L Pentastar V6 in the Pacifica has well-documented, serious mechanical weaknesses that often lead to misfire codes like P0304. The two most significant issues are valvetrain failure, where rocker arm bearings disintegrate causing the infamous 'Pentastar tick' and misfires, and a high rate of cylinder head or head gasket failures that allow coolant to leak into the cylinders. These issues are so prevalent that a P0304 code on this van requires a more thorough diagnosis beyond just swapping ignition parts. Technicians and owners report the head gasket issue often appears between 50,000 and 80,000 miles, sometimes presenting as a cold-start misfire that improves as the engine warms.

Symptoms You May Notice

• Rough or shaking idle
• Hesitation or stumbling during acceleration
• Flashing or solid Check Engine Light
• Noticeable loss of power
• Engine ticking noise (if related to valvetrain)
• Unexplained coolant loss (if related to head gasket)
• Misfire is most noticeable on a cold start and may improve as the engine warms (head gasket symptom).
• Sweet smell from the exhaust (coolant being burned).
• White smoke from the exhaust, especially on startup.
• Vehicle entering "limp mode" with a turtle icon displayed on the screen (as reported in NHTSA ODI #11719903).

Most Likely Causes

1. Failed Cylinder Head / Leaking Head Gasket 🔴 High Probability → Shop Engine Cylinder Head This platform has a widely reported issue of head gasket and/or cylinder head failure, often between 50,000 and 80,000 miles, which can cause coolant to leak into a cylinder and trigger a misfire. Cylinder 4 is a commonly cited location for this failure. Some technicians attribute this to a cylinder head design flaw that damages the gasket over time. The issue often starts as a misfire on a cold engine that goes away as the metal expands with heat.
   How to confirm: Check for signs of coolant loss in the reservoir, a sweet smell from the exhaust, or white smoke. Also, check the oil filler cap and dipstick for a milky, frothy residue, which indicates coolant has mixed with the oil. A definitive diagnosis requires a cooling system pressure test to see if it holds pressure and a chemical block test to check for exhaust gases in the coolant. A cylinder leak-down test is the most conclusive diagnostic step. NHTSA ODI #11719903 describes a case where a P0304 was diagnosed as a leaking head gasket causing coolant contamination of the engine oil.
   Typical fix: Requires replacing the head gasket and machining or replacing the cylinder head. 🎬 Watch: Step-by-step guide to replacing Pentastar head gaskets This is a major repair, often costing thousands of dollars. The redesigned left cylinder head for earlier Pentastar models with this issue is part number RL141353AC.
   Est. part cost: $200-$400 for a head gasket set.
2. Failed Rocker Arm / Lifter 🔴 High Probability → Shop Engine Rocker Arm The 3.6L Pentastar engine is known for premature failure of the rocker arm needle bearings, which causes the arm's roller to fail. This creates excessive valvetrain noise (the 'Pentastar tick') and can lead to misfires and camshaft damage. The issue is widespread enough that multiple class-action lawsuits have been filed. The failure introduces metal debris into the oil, which can cause further engine damage if not addressed.
   How to confirm: Listen for a distinct, rhythmic ticking or tapping sound from the top of the engine that increases with RPM. The sound can be mistaken for a noisy fuel injector, but the rocker arm tick is typically louder. Diagnosis is confirmed by removing the valve cover to inspect the rocker arms and camshaft lobes for wear, scoring, and dropped roller bearings. 🎬 See this walkthrough on replacing rocker arms, lifters, and camshafts
   Typical fix: Replace all rocker arms and hydraulic lifters on the affected cylinder head (Bank 2). If the rocker arm has damaged the camshaft, the camshaft must also be replaced. An oil and filter change is critical after the repair to remove metal debris.
   Est. part cost: $150-$300 for a full set of rockers and lifters for one head.
3. Faulty Ignition Coil 🟡 Medium Probability → Shop Ignition Coil
   How to confirm: Swap the ignition coil from cylinder #4 with another cylinder on the same bank (e.g., cylinder #2 or #6). Clear the codes and drive. If the code changes to P0302 or P0306, the ignition coil is the culprit. Also inspect the coil boot for oil saturation, which indicates a leaking valve cover gasket.
   Typical fix: Replace the faulty ignition coil. Accessing the front bank requires removing the upper intake manifold.
   Est. part cost: $40-$80
4. Worn or Defective Spark Plug 🟡 Medium Probability → Shop Spark Plug TSB 09-013-20 REV. A was issued for 2020-2021 models that may have been built with defective spark plugs that can crack internally, causing misfires.
   How to confirm: After confirming the coil is good, remove the spark plug from cylinder #4. Inspect it for wear, fouling (it may be wet with coolant if the head gasket is leaking), or cracks in the ceramic. Compare it to a new plug. The service interval for these plugs is 100,000 miles, but they can fail earlier.
   Typical fix: Replace the spark plug. It is recommended to replace all six plugs at the same time if they are near their service life. If a plug is fouled with coolant or oil, the underlying leak must be addressed.
   Est. part cost: $10-$25 per plug.

Rare But Worth Checking

• Clogged or Faulty Fuel Injector: → Shop Fuel Injector While less common than ignition or mechanical failures, a fuel injector can become clogged or fail electrically, preventing the correct amount of fuel from reaching cylinder #4. This can be tested by swapping the injector with another cylinder, similar to an ignition coil test, though it is much more labor-intensive.
• Intake Manifold Gasket Leak: → Shop Engine Intake Manifold A vacuum leak from a failed lower intake manifold gasket near the port for cylinder #4 can lean out the air/fuel mixture and cause a misfire. This can sometimes be detected by spraying a non-flammable substance like brake cleaner near the gasket mating surface while the engine is running and listening for a change in idle.
• Failed Oil Cooler Housing: The 3.6L Pentastar has an oil cooler assembly located in the engine valley that is prone to cracking. This can cause oil and coolant to mix, leading to overheating and other engine problems that could manifest as a misfire. Symptoms are similar to a head gasket failure (milky oil, oily coolant). An owner report in NHTSA ODI #11552765 notes a P0304 misfire occurring alongside an oil cooler failure and loss of coolant.

Diagnosis Steps

1. Read the code with an OBD-II scanner and confirm P0304 is present. Note any other codes and check freeze frame data to see when the misfire occurs (e.g., cold start). Manufacturer Bulletin #09-011-25 confirms that P0304 is a primary diagnostic code for customers commenting on a rough idle.
2. Perform a visual fluid check. Inspect the coolant reservoir for low levels or an oily film. Check the oil dipstick and filler cap for a milky, white, or brown sludge. These are strong indicators of a head gasket or oil cooler failure.
3. Listen carefully to the engine at idle and with light revs. A rhythmic ticking noise strongly points to a rocker arm/lifter issue.
4. To test the ignition system, you must first remove the upper intake manifold to access the front bank of cylinders (2, 4, 6).
5. Swap the ignition coil from cylinder #4 with the coil from cylinder #2 or #6. Reassemble, clear the codes, and drive. If the code returns as P0302 or P0306, the coil is bad.
6. If the code remains P0304, swap the spark plugs between the same cylinders. If the code changes, the spark plug was the issue.
7. If the misfire remains on cylinder #4 after swapping ignition components, the problem is likely mechanical or fuel-related.
8. Perform a cooling system pressure test. Pressurize the system to the specification on the radiator cap and see if it holds pressure. A loss of pressure indicates a leak, which could be the head gasket.
9. Perform an engine compression test on cylinder #4 and compare it to adjacent cylinders. A significant loss of compression (typically >15-20% difference) indicates an internal engine problem.
10. For a more definitive diagnosis, perform a cylinder leak-down test. This can pinpoint whether the leak is from intake valves, exhaust valves, piston rings, or the head gasket.
11. If a rocker arm failure is suspected, remove the valve cover to visually inspect the rocker arms and camshaft lobes for scoring or damage.

Parts You'll Likely Need

• Ignition Coil (OEM #68223569AD) — A common failure point for single-cylinder misfires. It's a primary suspect after ruling out spark plugs.
  Trusted brands: Mopar, NGK, Bosch, Delphi
  OEM price range: $80-$120
  Aftermarket price range: $40-$70
• Spark Plug (OEM #SP142582AC (NGK ILZKR7B11)) — A standard maintenance item that can wear out or fail, causing a misfire. It's the simplest and most inexpensive part to replace. Some model years had defective plugs from the factory.
  Trusted brands: NGK, Champion, Autolite
  OEM price range: $20-$30
  Aftermarket price range: $10-$20
• Rocker Arm (OEM #68272236AA) — A known major failure point on the 3.6L Pentastar engine that directly leads to misfires and ticking noises.
  Trusted brands: Mopar, Melling
  OEM price range: $25-$35 per arm
  Aftermarket price range: $15-$25 per arm
• Cylinder Head Gasket Set — Required for the common head gasket failure. The kit includes the head gasket, intake and exhaust manifold gaskets, valve cover gaskets, and other seals needed for the job.
  Trusted brands: Mopar, Fel-Pro, Mahle
  OEM price range: $300-$500
  Aftermarket price range: $150-$300

Related Codes That Often Appear With This One

• P0300 — If the underlying mechanical issue, like a failing valvetrain or head gasket, begins to affect multiple cylinders, a P0300 (Random/Multiple Cylinder Misfire) may accompany the P0304 code.
• P0302, P0306 — Since cylinders 2, 4, and 6 are on the same bank, issues like a leaking intake gasket or a failing cylinder head on that bank can cause misfires on adjacent cylinders. Early Pentastar cylinder head failures were most common on the left bank (2-4-6).

Technical Service Bulletins (TSBs) & Recalls

• TSB 09-013-20 REV. A: Notes that 2020-2021 models may have been built with defective spark plugs that can crack and cause misfires, specifically listing P0304 as a potential code.
• Bulletin #09-011-25: A manufacturer service bulletin noting that customers may comment on a rough idle associated with DTC P0304.
• TSB 18-022-21: A PCM software update for Ram trucks with the 3.6L engine to address various misfire codes, including P0304, especially after a cold start.
• Chrysler Extended Warranty X56: While for older (2011-2013) Pentastar engines, this highlights the history of cylinder head issues by extending the warranty to 10 years/150,000 miles for a specific left head failure that caused misfires.

Platform-Specific Known Issues

• Pentastar Tick / Valvetrain Failure: The 3.6L V6 is notorious for a ticking sound caused by failing rocker arm bearings. This is not just a noise; it's a mechanical failure that leads to misfires and can destroy the camshaft if ignored. A class-action lawsuit specifically addresses this issue.
• Premature Head Gasket Failure: Numerous owner and technician reports indicate a high failure rate for head gaskets on this engine, often occurring with relatively low mileage (50k-80k miles). This is considered a pattern failure by many in the independent repair community.

Mechanic-Grade Diagnostic Values

• Fuel Pressure (at fuel rail) — expected: Approximately 58 psi. Failure: Significantly lower pressure (e.g., below 40 psi) points to a weak fuel pump or clogged filter.
• Short-Term and Long-Term Fuel Trims — expected: Between -5% and +5% at idle on a warm engine.. Failure: High positive values (e.g., >10%) on the bank containing cylinder 4 could indicate a vacuum leak affecting that bank.
• Cylinder Compression (Minimum) — expected: Compression should be above 100 psi and within 25% of the highest reading cylinder.. Failure: A reading on cylinder 4 that is significantly lower than other cylinders indicates a mechanical engine problem.

Hidden / Shadow Codes Worth Checking

• Mode 6, Test ID $0D: This is not a DTC, but a data parameter in Mode 6 that tracks the raw misfire count for cylinder 4. Test IDs $0A through $0F correspond to cylinders 1 through 6. Monitoring $0D can show if misfires are occurring even if they aren't frequent enough to set a P0304 code. (see via Requires a scan tool with Mode 6 capabilities, such as the dealer-level wiTECH or other advanced consumer tools.)

Scan Tool Commands That Help

• wiTECH or equivalent advanced scanner: Fuel Injector Kill / Power Balance Test — This bidirectional command allows a technician to disable the fuel injector for cylinder 4 while the engine is running. If the engine's idle quality does not change when the injector is killed, it confirms that cylinder 4 was not contributing power, pointing towards a spark or compression issue rather than a fuel injector problem.

Wiring & Ground Locations

• G102 — Left side of the engine compartment.. A poor engine ground can cause a host of electrical issues, including weak spark or erratic sensor readings that could lead to a misfire code. While not specific to cylinder 4, checking the main engine grounds is a valid step when electrical causes are suspected.
• Cylinder 4 Ignition Coil Connector — On the front bank of the engine (near the radiator), middle cylinder. Requires removal of the upper intake manifold to access.. The connector and its wiring are the direct link for providing power and signal to the ignition coil. A visual inspection for corrosion, damage, or loose pins is crucial before replacing the coil itself.

Real Owner Repair Stories

• Chrysler Minivan Forum user 'Flgators2904' (2015 Chrysler Town & Country Platinum Limited (same 3.6L Pentastar engine family)) — P0304 code for cylinder 4 misfire.
  ❌ Tried (didn't work) Replaced all ignition coils, Replaced all spark plugs
  ✅ What actually fixed it The dealer diagnosed and replaced a failed left cylinder head. The owner reported that Chrysler covered the cost of the part, and the owner paid for labor, suggesting it was a known issue even on a 2015 model.
• NHTSA ODI #11484102 — An owner reported the van started running slightly rough in the mornings when the engine was cold, eventually setting a P0304 code. Despite replacing ignition coils and spark plugs at 80,000 miles, the issue persisted.
• NHTSA ODI #11552765 — An owner reported a failed cylinder head and P0304 misfire at 71,000 miles, requiring an engine rebuild or replacement, noting it occurred alongside an oil cooler failure.

OEM Part Supersession History

• 5184296AD, AE, AF, AG → 5184296AH — The original rocker arm design was prone to premature failure of the needle bearings in the roller. The updated 'AH' version is intended to have improved durability.
  Heads up: Beware of counterfeit parts sold online that claim to be the correct part number but have incorrect physical geometry. Installing these can prevent valves from closing properly.

Model Year Variations Within This Range

• 2017-present (engine change from 2016): The 3.6L Pentastar engine was significantly updated for the 2016 model year, which applies to all Pacificas in this range. Changes included a two-stage variable valve lift (VVL) system, a higher compression ratio (11.3:1 vs 10.2:1), new injectors, and new ignition coils. This means parts and diagnostic approaches for pre-2016 Pentastars may not be identical.
• 2021-present: A facelift for the 2021 model year introduced new exterior styling and the option for All-Wheel-Drive (AWD) on gasoline models. While the core engine remained the same, the AWD system adds complexity to the drivetrain, though it is not known to directly affect the P0304 causes.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Transmission Shudder, Harsh Shifting, or Failure 🔴 High — Commonly reported, especially in 2017-2018 models with the 9-speed automatic. Hybrid eCVT models also have significant issues. (Ref: Recall 23V-010 (NHTSA ID) for Hybrid models due to wiring short causing stall. Multiple software update TSBs exist for the 9-speed.)
• Engine Stalling / Sudden Shutdown 🔴 High — A significant issue, particularly for hybrid models, leading to a major recall. Can also affect non-hybrid models. (Ref: NHTSA Recall 23V-010 for 2017-2023 Hybrids.)
• Uconnect Infotainment System Glitches 🟠 Medium — Widespread reports of the screen freezing, rebooting, or becoming unresponsive across multiple model years. (Ref: Various software update TSBs have been released to address stability.)
• Power Sliding Door Malfunctions 🟠 Medium — Frequently reported issue where doors fail to open, close, or latch properly.
• Excessive Oil Consumption 🟠 Medium — Some owners report needing to add oil between scheduled changes. (Ref: Generally handled on a case-by-case basis under warranty if consumption is proven to be excessive.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this repair, used parts are generally not recommended for the most common failure items. A used intake manifold or wiring harness from a verified, low-mileage donor could be a cost-effective choice if they are the cause. However, the primary culprits (rocker arms, head gaskets) should always be replaced with new parts.

Donor-vehicle mileage cap: roughly under 60000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Verify the donor vehicle's VIN to confirm the year and engine version.
• For any mechanical part, look for a vehicle with no signs of front-end collision or fire.
• If buying a major component like a cylinder head, request to see the donor vehicle's maintenance records if possible.
• Inspect electrical connectors for corrosion, brittleness, or cut wires.

OEM-only on this vehicle (don't cheap out):

• Rocker Arms / Lifters: Due to the known design flaw and the high labor cost, using only the latest OEM revision (5184296AH) is critical to prevent a repeat failure.
• Head Gasket / Cylinder Head Bolts: These are single-use, critical components. Never reuse them. Always use new, quality parts for a head gasket job.
• Cylinder Head: While a used head is possible, the high failure rate on this engine makes it risky. A new or professionally remanufactured head with the updated design is the safest bet.

Aftermarket brands forum-validated for this vehicle:

• Valve Cover Gaskets: Fel-Pro, Mahle
• Ignition Coils: NTK, Delphi
• Spark Plugs: NGK, Champion (as per OEM spec)

Brands owners have reported issues with on this vehicle:

• Unbranded/white-box rocker arms from online marketplaces. There are documented cases of parts with correct numbers but incorrect physical profiles, leading to catastrophic engine damage.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0300 — Random or Multiple Cylinder Misfire; often accompanies P0304 if the head gasket failure or rocker arm debris affects multiple cylinders on Bank 2.
• P0302 — Cylinder 2 Misfire; located on the same cylinder bank (Bank 2) as cylinder 4. Used during diagnostic 'coil swapping' to confirm if a fault moves between cylinders.
• P0306 — Cylinder 6 Misfire; also located on Bank 2. Often checked alongside P0304 when diagnosing valvetrain issues or performing ignition component swaps.
• P0301 — Cylinder 1 Misfire; though on the opposite bank, it may appear if general Pentastar valvetrain or spark plug defects are widespread across the engine.

Frequently Asked Questions