P0305 on 2015-2020 Ram 2500: Cylinder 5 Misfire Causes and Fixes

What's Unique About the 2015-2020 Ram 2500

For the Ram 2500, the cause of P0305 is entirely dependent on the engine. For the 5.7L and 6.4L HEMI V8s, the cause is typically a simple ignition component. However, these engines are also widely known for a specific mechanical failure where a collapsed lifter damages the camshaft, leading to a persistent misfire often accompanied by a distinct ticking sound (the "HEMI tick"). For the 6.7L Cummins diesel, the fault is almost always related to the high-pressure fuel system, with a failing fuel injector being the most common culprit.

Diagnostic Flowchart

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

Generation note: This range covers the fourth generation (2015-2018) and the fifth generation (2019-2020) Ram 2500. The primary engines (6.4L HEMI, 6.7L Cummins) and their common issues 🎬 Watch: Common 6.4L HEMI engine failures to watch out for related to P0305 are largely consistent across this period. The 5.7L HEMI was phased out of the 2500 series after the 2018 model year. For the 6.4L HEMI, a significant change occurred in 2019 with the introduction of the ZF 8-speed transmission, replacing the previous 6-speed, which improved drivability but did not fundamentally change the engine's misfire causes.

Symptoms You May Notice

• Flashing or solid Check Engine Light
• Rough or shaky idle
• Engine hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Smell of raw fuel from the exhaust
• Decreased fuel economy
• Rhythmic ticking or tapping noise from the engine bay, especially on HEMI engines

Most Likely Causes

1. Failed Ignition Coil (HEMI Engines) 🔴 High Probability → Shop Ignition Coil Coil-on-plug systems are subjected to intense heat cycles and vibration, making them a common failure point on modern engines like the HEMI. This is the most common first-step diagnosis.
   How to confirm: Swap the ignition coil from cylinder 5 with another cylinder (e.g., cylinder 3). Clear the codes and run the engine. If the misfire code moves to P0303, the coil is bad.
   Typical fix: Replace the faulty ignition coil. The OEM Mopar part number is 68238603AA, which supersedes several previous part numbers.
   Est. part cost: $40-$90
2. Worn or Fouled Spark Plugs (HEMI Engines) 🔴 High Probability → Shop Spark Plug HEMI engines use two spark plugs per cylinder, doubling the chance of a plug-related issue. They are a routine maintenance item that is often overlooked, with a recommended service interval of 100,000 miles for the 6.4L.
   How to confirm: After ruling out the coil, swap the spark plugs from cylinder 5 with another cylinder. If the misfire code follows the plugs, they are the cause. Visually inspect the plug for wear, carbon tracking, oil fouling, or physical damage.
   Typical fix: Replace the spark plugs. It is highly recommended to replace all 16 spark plugs at the same time for consistent performance.
   Est. part cost: $80-$160 for a full set of 16
3. Failed Fuel Injector (Cummins Engine) 🔴 High Probability → Shop Fuel Injector The high-pressure common rail fuel system on the Cummins is sensitive to fuel quality and filtration. Contamination or simple wear and tear can lead to premature injector failure, making it the most common cause of a single-cylinder misfire on this engine.
   How to confirm: Diagnosis often requires a capable scan tool to perform an injector kill test or a cylinder contribution test. A more involved method is to swap the injector with another cylinder and see if the misfire code follows. A professional can also perform an injector return flow test; a maximum of 210 mL in 30 seconds is allowed for all injectors combined, with any single injector contributing more than 40 mL being considered excessive.
   Typical fix: Replace the faulty fuel injector and the high-pressure connector line. The Bosch OEM new injector for 2013-2018 models is part number 0445120342. The high-pressure line for cylinder #5 is Cummins part 4935974 (for 2007.5-2018) or Mopar 68480000AA (for 2019+). This is often a job for a professional due to the high pressures and special tools involved.
   Est. part cost: $400-$700
4. Failed Camshaft Lobe / Collapsed Lifter (HEMI Engines) 🟡 Medium Probability → Shop Engine Camshaft This is a well-documented major issue on 5.7L and 6.4L HEMI engines. The needle bearings in the roller lifters can fail, causing the roller to seize and grind down the camshaft lobe. This prevents the valves from opening correctly, causing a persistent mechanical misfire. The issue is so common that owners on forums frequently diagnose it based on the P0305 code combined with a ticking sound.
   How to confirm: A persistent ticking noise that increases with engine speed is a strong indicator. A compression test on cylinder 5 will show lower readings than other cylinders. Visual inspection after removing the valve cover and intake manifold is required to confirm the damaged lifter and cam lobe.
   Typical fix: This is a major engine repair that involves replacing the camshaft, all lifters, head gaskets, and related components. Many owners opt to install non-MDS lifters or upgraded aftermarket lifters for improved durability.
   Est. part cost: $800-$2000 for a complete kit

Rare But Worth Checking

• Faulty Fuel Injector (HEMI Engines): → Shop Fuel Injector While less common than ignition issues, a clogged or failed fuel injector can cause P0305. TSB 14-003-22 REV. A was issued for some 2021 6.4L engines for high-flow injectors causing misfires. It should be investigated after spark and coil are ruled out. One owner confirmed a new injector fixed a persistent P0305 after plugs and coils were replaced.
• Vacuum Leak: A leak in a vacuum hose or intake manifold gasket near cylinder 5 can lean out the air-fuel mixture and cause a misfire. A failing PCV valve can also act as a vacuum leak.
• Low Compression: If not caused by a cam/lifter failure, low compression can result from a burnt valve, damaged piston, or a failed head gasket. A compression test is required for diagnosis.
• Injector Wiring Harness (Cummins Engine): On the 6.7L Cummins, the injector wiring is integrated into the valve cover gasket. Over time, the wiring for a specific cylinder can break, causing an intermittent connection and a misfire code. This would typically be accompanied by code P0205.

Diagnosis Steps

1. Identify your engine (HEMI gas or Cummins diesel) as the next steps differ significantly.
2. For HEMI Engines: Listen for a rhythmic ticking noise that increases with engine speed. If present, immediately suspect a camshaft/lifter issue and proceed with caution.
3. Swap the ignition coil from cylinder 5 (third from front, driver's side) with an adjacent cylinder (e.g., cylinder 3). Clear codes and run the engine. If the misfire code moves (e.g., to P0303), the coil is bad.
4. If the code remains on P0305, swap the spark plugs between the same two cylinders. If the code moves, the spark plug was the issue. Inspect the plug for fouling or damage.
5. Inspect the wiring and connector for the cylinder 5 ignition coil and fuel injector for any visible damage, corrosion, or loose connections.
6. If the misfire persists, perform a compression test on cylinder 5. A result significantly lower than other cylinders points to a mechanical problem (valves, piston, or the common cam/lifter failure).
7. If compression is good, consider a faulty fuel injector. You can swap the injector with another cylinder to see if the misfire follows, though this is more labor-intensive.
8. For Cummins Engines: Check fuel quality and ensure fuel filters have been replaced at the proper interval. A clogged filter can strain the entire system.
9. Use a high-end scan tool to perform a cylinder contribution test to confirm cylinder 5 is underperforming.
10. The most likely cause is the fuel injector for cylinder #5 (fifth from front). Diagnosis can be confirmed by swapping the injector with another cylinder, but this is a complex job best left to professionals familiar with high-pressure fuel systems.

Parts You'll Likely Need

• Ignition Coil (HEMI) (OEM #68238603AA) — This is the most common and easiest-to-diagnose cause of a single-cylinder misfire on the 5.7L and 6.4L HEMI engines.
• Spark Plugs (HEMI) (OEM #SP142510AC (6.4L)) — Worn or fouled spark plugs are a common maintenance-related cause of misfires. All 16 should be replaced as a set.
• Fuel Injector (Cummins) (OEM #0445120342 (Bosch OEM for 2013-2018)) — This is the most probable cause for a P0305 on the 6.7L Cummins engine.
• Camshaft and Lifter Kit (HEMI) — Required for the common cam/lifter failure. Many owners upgrade to non-MDS lifters like Mopar part 5038784AD for improved durability.

Related Codes That Often Appear With This One

• P0300 — If the misfire becomes more widespread due to a systemic issue like a major vacuum leak or significant valvetrain damage, a P0300 (Random/Multiple Cylinder Misfire) code may appear alongside P0305.
• P0205 — This code for 'Injector Circuit/Open - Cylinder 5' points specifically to an electrical problem with the fuel injector or its wiring. Seeing it with P0305 strongly suggests the injector or its harness is the root cause, not spark or compression.

Technical Service Bulletins (TSBs) & Recalls

• 1810222REVA
• 1806623
• 1813022REVA
• 1810722REVA
• 1810122REVA
• 14-003-22 REV. A: Addresses '6.4L Fuel Injector High Flow Misfire' for some 2021 vehicles, where faulty injectors cause misfire codes including P0305.

Platform-Specific Known Issues

• The 5.7L and 6.4L HEMI engines are widely documented to suffer from premature camshaft and lifter failure. A single-cylinder misfire code like P0305, especially when paired with an engine tick, is a classic symptom of a failed roller lifter on cylinder #5, which then destroys the camshaft lobe.

Mechanic-Grade Diagnostic Values

• Fuel Injector Resistance (6.4L & 5.7L HEMI) — expected: 11-15 Ohms. Failure: An infinite reading (OL) indicates an open/failed injector.
• Fuel Injector Resistance (6.7L Cummins) — expected: Less than 1.0 Ohm. Failure: A reading significantly higher than 1.0 Ohm or an open circuit (OL) indicates a failed injector.
• Ignition Coil Primary Resistance (HEMI) — expected: Approximately 0.52Ω - 0.8Ω. Failure: Significant deviation from the expected resistance can indicate a failing coil.
• Cummins Injector Return Flow (Running Test) — expected: Maximum 210 mL in 30 seconds for all injectors combined.. Failure: Exceeding 210 mL total, or having one injector contribute more than 40 mL, indicates excessive leakage and a bad injector.
• Cummins Cranking Fuel Rail Pressure — expected: Approximately 4,000 PSI. Failure: Failure to build around 4,000 PSI during cranking can prevent the engine from starting, often due to leaking injectors.

Scan Tool Commands That Help

• wiTECH or equivalent high-end scanner: Cylinder Contribution Test / Injector Kill Test — Used to electronically disable individual injectors to confirm which cylinder is not contributing to engine power. This is a primary diagnostic step for both HEMI and Cummins engines to isolate the misfiring cylinder without disassembly.
• wiTECH or equivalent high-end scanner: Fuel Pressure Override Test (Cummins) — This command forces the fuel system to its maximum pressure (approx. 26,000 PSI) to perform an injector return flow test, which is crucial for diagnosing leaking injectors on the Cummins engine.
• wiTECH or equivalent high-end scanner: View Misfire Counters (Live Data) — Before and after swapping components (like an ignition coil), monitoring the live misfire count for cylinder 5 versus the cylinder you swapped with provides instant feedback on whether the fault has moved, confirming the bad part.

Wiring & Ground Locations

• Cylinder 5 Fuel Injector Connector (HEMI) — On top of the engine, on the driver's side fuel rail, at the third injector from the front.. This connector and its wiring are the primary electrical link for the cylinder 5 fuel injector. Damage, corrosion, or looseness here will cause P0305 and potentially P0205.
• G300 — Under the vehicle at the driver door on a body mount.. While there are over 50 grounds on the truck, major body and chassis grounds like G300 can cause unpredictable electronic issues if they become loose or corroded. While not a primary suspect for a single-cylinder misfire, it's a location to check if multiple, seemingly unrelated electrical issues are present.
• Injector Wiring Harness (Cummins) — Integrated into the valve cover gasket, with a pass-through connector on the exterior of the valve cover.. This harness is a very common failure point. The wiring for cylinder 5 can break or short inside the valve cover, causing a persistent P0305 and/or P0205. Checking continuity from the external connector to the injector itself is a key diagnostic step.

Real Owner Repair Stories

• 5thGenRams Forum user (Ram 2500 with 115,000 miles) — P0305 misfire at low idle that only occurs after the truck warms up. Runs great at higher RPM.
  ❌ Tried (didn't work) Replaced all 16 spark plugs, Replaced the ignition coil for cylinder 5
  ✅ What actually fixed it Replacing the fuel injector for cylinder #5 resolved the misfire. The user noted the local dealer had 32 of these injectors in stock, suggesting it's a relatively common replacement part.
• RamForum user 'huntergreen' (2010 Ram 1500 5.7L HEMI (similar engine, relevant failure mode)) — Flashing check engine light with P0305 under acceleration (2k-3.5k RPM), hesitation, and a noticeable engine tick from the #5 cylinder area.
  ❌ Tried (didn't work) Replaced spark plugs, Swapped ignition coil with another cylinder, Swapped fuel injector with another cylinder
  ✅ What actually fixed it The final diagnosis pointed to a lifter/camshaft failure. The recommended next step was to remove the valve cover to visually inspect the rocker arm movement to confirm the mechanical failure.
• Reddit user in r/ram_trucks (2014 Ram 5.7L HEMI (similar engine, relevant failure mode)) — Initial P0305 misfire due to lifter failure. After replacing the camshaft and lifters with an aftermarket kit, the truck had new misfires on cylinders 1 and 4.
  ❌ Tried (didn't work) Re-checking engine timing, Replacing an MDS solenoid
  ✅ What actually fixed it The problem was a defective *new* lifter from the aftermarket kit. The issue was ultimately resolved by replacing the aftermarket lifters with genuine MOPAR 'Hellcat' lifters.

When the Usual Fixes Don't Work

• While ignition components are the most common cause of P0305 on a HEMI, a forum user with a 2015+ Ram 2500 reported that after replacing spark plugs and the cylinder 5 coil, the misfire persisted. The issue was only resolved by replacing the cylinder 5 fuel injector. This serves as a strong reminder to not rule out fuel system issues on the gas engine, even though they are less common than on the Cummins.

OEM Part Supersession History

• 56029129AA, 56029129AB, 56029129AF, 68060346AA → 68238603AA — Standard part evolution for improved reliability and manufacturing consistency for the HEMI ignition coil.
• Various MDS lifter part numbers (e.g., 53021720AE) → 5038784AD (Non-MDS 'Hellcat' lifter) — Many owners and shops proactively replace the failure-prone MDS lifters with the more robust non-MDS 'Hellcat' lifters during a camshaft repair to prevent future failures.
  Heads up: Using these non-MDS lifters requires the Multi-Displacement System (MDS) to be electronically disabled in the PCM using a tuner. Failure to do so will result in fault codes and improper engine operation.

Model Year Variations Within This Range

• 2019-2020: For the 6.4L HEMI, the 2019 model year marked the shift from the 66RFE 6-speed automatic transmission to the ZF 8HP75 8-speed automatic. While this significantly changed the truck's driving characteristics and shift points, the engine itself and its common causes for P0305 (coils, plugs, cam/lifters) remained the same.
• 2015-2018: The 5.7L HEMI V8 was available in the Ram 2500 through the 2018 model year but was discontinued for the 2500 series starting in 2019.