P0304 on 2021-2025 Ram 1500: Cylinder 4 Misfire Causes and Fixes

What's Unique About the 2021-2025 Ram 1500

For the 2021-2025 Ram 1500, P0304 points to two very different, but common, narratives. Several Technical Service Bulletins (TSBs) address software issues where a misfire on cylinder 4 (and others) can occur during a cold start, which is fixable with a PCM reprogram from a dealer. However, on the popular 5.7L HEMI V8, a P0304 code is also a well-documented symptom of a failing MDS (Multi-Displacement System) lifter. This failure is often attributed to lubrication issues at low RPMs and extended idle times, where a lifter's roller can stop spinning and grind a flat spot onto the camshaft lobe 🎬 Watch: A deep dive into the Hemi tick and engine protection., causing a persistent misfire and the infamous 'Hemi tick'.

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.
• Hesitation or stumbling during acceleration.
• Noticeable loss of power.
• Check engine light is on and steady, or flashing under load.
• An unusual exhaust smell, sometimes like rotten eggs or gasoline.
• For 5.7L HEMI, a distinct 'ticking' or 'clacking' sound from the engine, which may get more pronounced as it warms up.
🎬 See this video to help distinguish lifter noise from exhaust leaks.
• Vehicle may enter a 'limp mode' with reduced power and altered shifting behavior.

Most Likely Causes

1. Worn Spark Plug 🔴 High Probability Spark plugs are a routine maintenance item and a primary point of failure for any ignition system. The 5.7L HEMI uses two plugs per cylinder, but a failure of the primary plug is enough to cause a misfire.
   How to confirm: Remove the spark plug from cylinder 4 and inspect it for wear, fouling, or damage. A simple diagnostic step is to swap the spark plug with another cylinder (e.g., cylinder 2) and see if the misfire code changes to P0302.
   Typical fix: Replace the spark plug in cylinder 4. It is best practice to replace all spark plugs at the same time. 🎬 Watch: Step-by-step guide to replacing Hemi spark plugs and coils.
   Est. part cost: $5-$25 per plug
2. Faulty Ignition Coil 🔴 High Probability
   How to confirm: Swap the ignition coil from cylinder 4 with one from an adjacent, working cylinder (e.g., cylinder 2). Clear the codes and drive the vehicle. If the code changes to P0302, the coil is bad.
   Typical fix: Replace the faulty ignition coil. Many owners on forums report a bad coil pack as the fix.
   Est. part cost: $40-$100
3. PCM Software Update Needed 🟡 Medium Probability Multiple TSBs (#18-031-25 REV. A, #18-021-26, #18-031-25) have been issued for 2021-2025 models specifically for misfires (including P0304) that occur during cold start catalyst heating.
   How to confirm: This issue typically only occurs when the engine is cold, often within the first 30 seconds of starting. A Ram dealership can check your vehicle's VIN against their database for open TSBs or Rapid Service Updates (RSU).
   Typical fix: Reprogramming the Powertrain Control Module (PCM) with the latest available software.
   Est. part cost: $0 (if under warranty), $100-$250 (dealer labor)
4. Failed MDS Lifter / Camshaft Lobe (5.7L HEMI) 🟡 Medium Probability The Multi-Displacement System (MDS) lifters in the 5.7L HEMI are a known weak point, often due to lubrication issues at low RPM. A failed lifter can stop rotating and grind down the camshaft lobe, causing a persistent misfire. TSB #18-002-25 directly links P0304 with cylinder deactivation system codes.
   How to confirm: Listen for a loud, rhythmic ticking or clacking noise from the engine that may worsen as it warms up. A professional mechanic can confirm by removing the valve cover to inspect valve movement or, more definitively, by removing the cylinder head to inspect the lifters and camshaft.
   Typical fix: This is a major repair requiring replacement of all lifters (especially the MDS lifters) and often the camshaft as well.
   Est. part cost: $800-$2000+
5. Clogged or Faulty Fuel Injector ⚪ Low Probability Debris from fuel can clog injectors over time, leading to a lean misfire condition.
   How to confirm: Use a 'noid light' to verify the injector is receiving an electrical signal. To confirm a clog, the injector can be swapped with another cylinder, but this is more labor-intensive than swapping a coil or plug. A professional can perform a flow test.
   Typical fix: Clean or replace the fuel injector for cylinder 4.
   Est. part cost: $50-$150

Rare But Worth Checking

• Intake Manifold Gasket Leak: A vacuum leak near the intake runner for cylinder 4 can lean out the air/fuel mixture, causing a misfire. This can be diagnosed with a smoke test. One owner of a new Ram with the Hurricane engine and a P0304 found the cause to be a folded throttle body gasket, causing an air leak.
• Low Engine Compression: Internal mechanical problems like a worn piston ring, a leaking head gasket, or a damaged valve can cause a loss of compression, leading to a misfire. A compression test is needed to diagnose this. One Grand Cherokee owner with a P0304 found it was due to bad valves causing low compression on one bank of cylinders.

Diagnosis Steps

1. Scan the PCM for any other stored trouble codes to get more context. Codes like P3400 or P3425 are critical clues on a HEMI.
2. If the engine is a 5.7L HEMI, listen carefully for any ticking noises, especially as the engine warms up. A quiet tick when cold that gets louder can indicate a lifter issue.
3. Locate cylinder 4. On the 5.7L HEMI and 3.6L V6, it is the second cylinder back on the driver's side (left side) of the engine.
4. Swap the ignition coil from cylinder 4 with the coil from cylinder 2. Clear the codes and run the engine. If the code changes to P0302, the ignition coil is faulty.
5. If the code remains P0304, move the coil back and swap the spark plug from cylinder 4 with the one from cylinder 2. Clear codes and re-test. If the code is now P0302, the spark plug is the issue.
6. If the misfire persists on cylinder 4, inspect the wiring and connector for the fuel injector and ignition coil for any visible damage, chafing, or loose connections.
7. If the misfire only occurs on cold starts, contact a Ram dealer to check for available PCM software updates related to TSBs #18-031-25, #18-021-26, or #09-011-25.
8. If none of the above steps identify the problem, a more advanced diagnosis is needed. This includes testing the fuel injector, performing an engine compression test on cylinder 4, and (for HEMI engines) a physical inspection of the valvetrain and lifters.

Parts You'll Likely Need

• Ignition Coil (OEM #68238603AA) — A very common failure point for misfire codes. It's responsible for generating the high voltage for the spark plug.
  Trusted brands: Mopar, NGK, Delphi
  OEM price range: $60-$100
  Aftermarket price range: $40-$75
• Spark Plug (OEM #SP143877AB (for 5.7L HEMI, replaces 68143877ab)) — As a standard wear item, a fouled or worn spark plug is a primary cause of misfires.

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or begins to affect other cylinders, a P0300 (Random/Multiple Cylinder Misfire) may appear alongside P0304. This is common with both software issues and progressing mechanical failures.
• P3400 / P3497 — On 5.7L HEMI engines, these codes relate to the Cylinder Deactivation System. Their presence with P0304 strongly suggests a problem with the MDS lifters, as noted in TSB #18-002-25.
• P3425 — This code specifically points to a 'Cylinder 4 Deactivation Control Circuit' fault. If seen with P0304 on a 5.7L HEMI, it is a very strong indicator of a failed MDS solenoid or lifter for cylinder 4.

Technical Service Bulletins (TSBs) & Recalls

• TSB #18-031-25 REV. A: Addresses misfires on multiple cylinders (including P0304) during cold start catalyst heating, fixed by a PCM software update.
• TSB #18-002-25: Links P0304 with cylinder deactivation codes (P3400, P3497, P3425), pointing to MDS lifter issues or related software problems on the 5.7L HEMI.
• TSB #18-021-26: Also notes P0304 occurring during cold start catalyst heating, recommending a PCM software update.
• TSB #09-011-25: A general TSB for rough idle and various misfire codes, including P0304.
• TSB #18-046-24: Covers rough running and multiple misfire codes, including P0304.

Platform-Specific Known Issues

• Cold Start Misfires: Multiple TSBs confirm that a software glitch can cause P0304 and other misfire codes specifically during cold engine starts. The fix is a dealer-installed PCM software update. (TSBs #18-031-25 REV. A, #18-021-26, #18-031-25)
• 5.7L HEMI Lifter Failure: The MDS lifters are prone to failure, which often presents first as a single-cylinder misfire (like P0304) accompanied by a ticking noise. This is a well-documented issue across multiple forums and can lead to a very expensive camshaft replacement if not addressed. The issue is often linked to extended idling and oil viscosity.

Mechanic-Grade Diagnostic Values

• Fuel Injector Resistance — expected: 10 - 18 Ohms, with a more specific reading on a 2020 5.7L HEMI being around 11.5 Ohms.. Failure: A reading of 0 Ohms (short circuit) or infinite/OL (open circuit). Readings should be very similar across all injectors.
• Mode 6 Misfire Counter — expected: Zero or very low counts for each cylinder during the current and previous 10 driving cycles.. Failure: A significantly high number of misfire counts logged for cylinder 4 (e.g., Test ID $A6 for cylinder 4) compared to other cylinders, even if the Check Engine Light is not yet on.
• Ignition Coil Connector Voltage (Key On, Engine Off) — expected: One pin should show battery voltage (approx. 12V) from the ASD relay. The other pin is the control circuit from the PCM and will not show steady voltage.. Failure: No voltage on the power supply pin indicates a wiring or relay issue, not a faulty coil.

Hidden / Shadow Codes Worth Checking

• Mode 6, Test IDs $A2-$A9: These are not traditional codes but onboard diagnostic monitor results. Test IDs $A2 through $A9 correspond to misfire counts for cylinders 1 through 8. A technician can view these values to see if cylinder 4 is registering misfires before the count is high enough to trigger the P0304 DTC and illuminate the check engine light. (see via A professional-grade scan tool with Mode 6 data capability.)

Scan Tool Commands That Help

• wiTECH 2.0 (OEM Tool): PCM Reprogram/Flash — This is required to apply the fix for cold-start misfires as specified in multiple Technical Service Bulletins (TSBs). The dealer uses this function to load the updated software onto the vehicle's Powertrain Control Module.
• wiTECH 2.0 or advanced aftermarket scanner: Live Data > Misfire Counters — To monitor real-time misfire events on cylinder 4 and compare them to other cylinders while performing diagnostic tests (e.g., raising RPM, test driving under load). This helps confirm if a repair was successful or if the misfire is intermittent.
• wiTECH 2.0 or advanced aftermarket scanner: Cylinder Power Balance Test — This bidirectional test deactivates one cylinder at a time and measures the corresponding drop in engine RPM. A cylinder that causes little or no RPM drop when deactivated is the one that is misfiring. This can quickly confirm the location of the misfire without swapping parts.

Wiring & Ground Locations

• Main Engine/Body Grounds — Key locations include a ground strap from the engine block to the frame/firewall, and the primary battery negative cable connection to the chassis (often on the driver's side inner fender).. A corroded or loose ground can cause erratic behavior in the ignition and fuel systems, leading to intermittent misfires that are difficult to diagnose. The PCM and ignition coils rely on solid ground connections for accurate operation. Cleaning and tightening these grounds is a low-cost diagnostic step.
• Cylinder 4 Ignition Coil Connector — On the driver's side valve cover, second from the front of the engine.. The connector itself or its wiring can become damaged from heat and vibration, causing a poor connection to the coil. A visual inspection for cracked plastic, spread terminals, or chafed wires is crucial before replacing the coil.

Real Owner Repair Stories

• 5thGenRams.com forum user (2020 Ram 1500) — P0304 misfire code.
  ✅ What actually fixed it The user reported the cause was a bad ignition coil pack. Another user in the same thread confirmed a bad coil pack fixed their P0305 (cylinder 5) misfire at only 6,000 miles.
• YouTube channel 'ADVANCED LEVEL AUTO' (4th Gen Ram 1500 5.7L HEMI (diagnostic process is identical)) — Persistent P0301 (Cylinder 1 Misfire) that returned after initial checks.
  ❌ Tried (didn't work) Swapping spark plugs between cylinders.
  ✅ What actually fixed it The fuel injector from the misfiring cylinder (#1) was swapped with the injector from cylinder #3. The misfire code then changed to P0303, proving the fuel injector was faulty. Replacing the bad injector resolved the issue.
• YouTube channel 'Tony's Toolbox' (2013 Ram 1500 5.7L HEMI) — Loud ticking/knocking noise from the passenger side of the engine after a recent camshaft and lifter replacement.
  ❌ Tried (didn't work) The previous owner had already replaced the cam and lifters, but the noise returned.
  ✅ What actually fixed it Upon inspection, the rocker arm shafts had been installed improperly, causing several pushrods to become bent and damaged. Replacing the damaged pushrods and correctly installing the valvetrain components fixed the ticking and associated misfire.

OEM Part Supersession History

• 56029129AA, 56029129AB, 56029129AF, 68060346AA → 68238603AA — Standard part evolution for improved reliability or manufacturing changes.
  Heads up: The newest part number, 68238603AA, is the correct service replacement for the listed predecessors on 5.7L HEMI engines.

Model Year Variations Within This Range

• 2021-2025: Multiple software updates have been released to address cold start misfires (including P0304). A dealer must check the vehicle's VIN to see which specific TSB applies. For example, TSB #09-011-25 targets 2021 models, #18-021-26 targets 2022 models, and #18-031-25 REV. A covers a broader range including 2025 models.
• 2021: A specific recall (Chrysler recall 37A) was issued for some 2021 Ram 1500 models with the 5.7L eTorque engine for a PCM software issue that could cause an engine stall. While not directly for P0304, it highlights the importance of ensuring the PCM software is fully updated.