P0306 on 2021-2025 Ram 1500: Cylinder 6 Misfire Causes and Fixes

What's Unique About the 2021-2025 Ram 1500

For the 2021-2025 Ram 1500, a P0306 code isn't always a simple spark plug or coil issue. Ram has issued multiple Technical Service Bulletins (TSBs) indicating that misfires on cold starts can be due to a software glitch in the PCM that requires reprogramming by a dealer. Furthermore, on models with the 5.7L HEMI V8, a persistent P0306 code, especially if accompanied by a ticking noise, can be an early symptom of the well-documented 'Hemi Tick,' which involves a failed MDS lifter and subsequent camshaft damage. This is a widely discussed topic in owner forums, with many sharing experiences of this specific failure mode.

Diagnostic Flowchart

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

Symptoms You May Notice

• Check engine light is on or flashing.
• Rough or shaky idle.
• Engine hesitation or stumbling during acceleration.
• Noticeable loss of power
• Valvetrain ticking or tapping noise (especially on 5.7L HEMI), which may be more noticeable on cold starts. [6, 09-011-25]
• Reduced fuel economy.
• Engine running rough during warm-up phase.

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Coil-on-plug ignition systems are subjected to significant heat and vibration, leading to eventual failure. This is a common wear item on most modern engines and a frequent fix reported by owners.
   How to confirm: The easiest way to confirm a bad coil is to swap the ignition coil from cylinder 6 with another cylinder (e.g., cylinder 4). Clear the codes and drive the truck. If the code changes to P0304, the coil is the culprit. This is a standard diagnostic step recommended in many owner forums.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace them in sets if the vehicle has high mileage, though replacing just the failed one is also common.
   Est. part cost: $40-$90
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug The 5.7L HEMI uses two spark plugs per cylinder (16 total), increasing the statistical chance of a single plug failing. Plugs are a standard maintenance item and will eventually wear out. TSB 09-013-20 REV. A also notes internal cracks can cause misfires on the 3.6L V6.
   How to confirm: Remove the spark plug(s) from cylinder 6 and inspect for wear (worn electrode), carbon fouling, oil, or a cracked porcelain insulator. You can also swap the plugs to another cylinder to see if the misfire follows, a common DIY diagnostic step.
   Typical fix: Replace the spark plug(s). It is best practice to replace all 16 plugs on the 5.7L HEMI or all 6 on the 3.6L V6 at the same time.
   Est. part cost: $5-$25 per plug
3. PCM Software Update Needed 🟡 Medium Probability Multiple TSBs (#18-031-25 REV. A, #18-020-26, #18-002-25) have been issued by the manufacturer for misfires, including P0306, that occur specifically during cold start catalyst heating. The software updates adjust parameters to prevent these false misfire detections during the warm-up phase.
   How to confirm: This can only be confirmed by a Ram dealership or a qualified shop with access to OEM service information. They will check your vehicle's VIN-specific software version against the latest available updates mentioned in the TSBs.
   Typical fix: The dealer will reprogram or 'flash' the Powertrain Control Module (PCM) and/or the Ignition System Control Module (ISCM) with the latest software.
   Est. part cost: $0 (if under warranty) - $250
4. Failed Camshaft and/or Lifter (5.7L HEMI) 🟡 Medium Probability → Shop Engine Camshaft The 5.7L HEMI engine is known for a valvetrain issue, often called the 'Hemi Tick,' where the roller on a hydraulic MDS lifter fails, seizes, and grinds down the corresponding lobe on the camshaft. This is a well-documented and feared issue in owner forums, with some estimates suggesting a 5-10% failure rate.
   How to confirm: This is a serious mechanical issue. Diagnosis starts with listening for a distinct ticking noise from the top of the engine, especially when cold. If basic ignition/fuel swaps don't resolve the P0306, a compression test is needed. Low compression on cylinder 6 points towards a valvetrain problem. Final confirmation requires removing the valve cover to inspect valve movement and, ultimately, pulling the cylinder head to inspect the lifters and camshaft.
   Typical fix: This is an extensive and expensive repair that involves replacing the camshaft, all lifters (both MDS and standard), and related gaskets and seals. Some owners on forums report dealer quotes ranging from $5,000 to over $7,000 for this job.
   Est. part cost: $800-$2000+
5. Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector Injectors can become clogged over time or fail electronically, but it's less common than ignition component failure. Sometimes a P0206 (Injector Circuit Malfunction) code will accompany the P0306.
   How to confirm: After ruling out spark plugs and coils, you can swap the fuel injector from cylinder 6 with another cylinder. If the misfire code moves, the injector is bad. A mechanic can also perform a resistance test or an injector balance test. In one documented case, a dealership initially misdiagnosed an internal engine problem when the actual fix was a simple fuel injector replacement.
   Typical fix: Replace the faulty fuel injector. Using a quality fuel system cleaner like Redline SI-1 is sometimes suggested as a first step if the injector is merely clogged.
   Est. part cost: $70-$180

Rare But Worth Checking

• Failed Rocker Arm (3.6L Pentastar): → Shop Engine Rocker Arm The 3.6L Pentastar engine has a known issue with rocker arm bearing failure, which can cause a ticking noise and misfire codes. This can lead to camshaft damage if not addressed. While a class action lawsuit targeted earlier models, the underlying design is similar, making it a possibility on 2021+ trucks.
• Low Cylinder Compression: Beyond lifter failure, low compression can result from a burnt valve, leaking head gasket, or damaged piston rings. A compression test and cylinder leak-down test are required to diagnose this.
• Water Intrusion into Spark Plug Well: → Shop Spark Plug On some vehicle designs, a degraded cowl seal can allow rainwater to drip directly onto the engine and into the spark plug wells, shorting out the ignition coil and causing a misfire. While more common on older models like the Durango, it's a possibility to check for if the misfire appears after washing the truck or a heavy rain.

Diagnosis Steps

1. Read the code: Use an OBD-II scanner to confirm P0306 and check for any other pending or stored codes, such as P0300 or P3441, which provide critical context.
2. Identify Cylinder 6: On the 5.7L HEMI and 3.6L V6, cylinder 6 is the rearmost cylinder on the passenger side (Bank 2, closest to the firewall).
3. Swap the Ignition Coil: Swap the coil from cylinder 6 with the coil from cylinder 4 (the middle cylinder on the passenger side). Clear the codes and test drive. If the code returns as P0304, the coil is bad. This is the most common first diagnostic step.
4. Inspect/Swap Spark Plugs: If the misfire remains on cylinder 6, remove and inspect the two spark plugs. Look for wear, damage, or fouling. If unsure, swap the plugs with cylinder 4 and see if the code follows.
5. Check for TSBs: If the misfire primarily happens on cold starts, contact a Ram dealer and reference TSBs #18-031-25 REV. A and #18-020-26 to see if a PCM software update is needed. Provide your VIN.
6. Listen for the 'Hemi Tick': On 5.7L models, listen carefully to the top of the engine at idle, especially when cold. A distinct, rhythmic ticking or tapping noise is a strong indicator of a potential lifter/camshaft failure.
7. Check the Fuel Injector: If ignition components are good, you can swap the fuel injector from cylinder 6 with another cylinder to see if the code moves. You can also test the injector's resistance with a multimeter.

Parts You'll Likely Need

• Ignition Coil (OEM #68225727AA) — This is one of the most common failure points for a single-cylinder misfire. Heat and vibration cause them to fail over time.
  Trusted brands: Mopar, NGK, Delphi
• Spark Plug (HEMI V8) (OEM #SP143877AB) — Spark plugs are a routine maintenance item. The HEMI uses 16, increasing the chances of one failing. The correct OEM plug is crucial for proper performance.
  Trusted brands: Mopar (OEM), NGK
• Camshaft and Lifter Kit (HEMI V8) — In the case of the 'Hemi Tick', a complete kit including a new camshaft, all 16 lifters (MDS and non-MDS), head gaskets, and bolts is required for a proper repair.
  Trusted brands: Mopar, AMS Racing, Comp Cams

Related Codes That Often Appear With This One

• P0300 — If the misfire becomes more frequent or other cylinders begin to misfire, a P0300 (Random/Multiple Cylinder Misfire) code will often accompany P0306. This is mentioned in TSB #18-002-25.
• P030X (e.g., P0302, P0304) — It's common to see other specific cylinder misfire codes if the underlying cause (like a software issue, fuel delivery problem, or widespread valvetrain wear) affects more than just cylinder 6. [18-002-25]
• P3441 / P3497 — TSB #18-002-25 explicitly links misfire codes like P0306 with Cylinder Deactivation System codes on the 5.7L HEMI. P3441 is for Cylinder 6 Deactivation Control Circuit, and P3497 is for Bank 2, strongly suggesting a relationship with the MDS system and its components (lifters).
• P0206 — This code indicates a malfunction in the fuel injector circuit for cylinder 6. If seen with P0306, it points directly to the fuel injector or its wiring as the likely culprit.

Technical Service Bulletins (TSBs) & Recalls

• 18-031-25 REV. A: Addresses cold start misfires (including P0306) and recommends a PCM software update.
• 18-002-25: Lists P0306 as a possible DTC along with cylinder deactivation system codes.
• 09-011-25: Connects P0306 to symptoms of rough idle and valvetrain noise.
• 18-020-26: Notes that P0306-00 can be set during cold start catalyst heating.
• 18-031-25: Also mentions PCM and ISCM reprogramming for cold start misfires.

Platform-Specific Known Issues

• Cold Start Misfires: Per TSB #18-031-25 REV. A and #18-020-26, these trucks are prone to setting misfire codes like P0306 during cold starts due to PCM software logic. The fix is a dealer-installed software update.
• HEMI Lifter/Cam Failure: A significant number of 5.7L HEMI engines experience failure of the MDS (Multi-Displacement System) lifters. This can manifest as a P0306 code and a ticking sound, requiring major engine repair.
• Valvetrain Noise: TSB #09-011-25 explicitly links P0306 with customer complaints of rough idle and valvetrain noise, pointing towards potential mechanical engine issues. [09-011-25]

Mechanic-Grade Diagnostic Values

• 5.7L HEMI Ignition Coil Primary Resistance — expected: 0.558 - 0.682 Ohms at 70-80°F. Failure: A reading outside of this range indicates a faulty coil.
• 3.6L V6 Fuel Injector Resistance — expected: Approximately 12.0 - 12.5 Ohms. Failure: A significantly higher or lower reading, or an open circuit, points to a bad injector. One diagnostic video showed a bad injector reading over 21 Ohms while good ones were around 14 Ohms.
• 5.7L HEMI Fuel Pressure (Cranking/Running) — expected: 58 ± 5 PSI. Failure: Pressure significantly below 53 PSI indicates a weak fuel pump or clogged filter. One diagnostic video showed a pump barely making 30 PSI.

Hidden / Shadow Codes Worth Checking

• Mode $06, TID $53 (or similar): This is not a trouble code, but a diagnostic monitor that tracks the raw misfire count for each individual cylinder, even for misfires not severe enough to trigger a Check Engine Light. A high count on cylinder 6 (e.g., several hundred or thousands) when other cylinders are near zero confirms the issue is isolated to cylinder 6 before a P0306 code is officially logged. (see via Requires a professional-grade scan tool or a capable consumer OBD-II adapter paired with an app like Torque Pro. In the scan tool, navigate to "Mode $06" or "Test Results".)

Scan Tool Commands That Help

• wiTECH (Dealer Tool) or equivalent professional scanner: Fuel Injector Balance Test — This function allows the technician to individually disable each fuel injector. When cylinder 6's injector is disabled, if there is no change in engine RPM or smoothness, it confirms that the injector was not contributing, pointing to a failure in that injector or its circuit.
• wiTECH (Dealer Tool) or equivalent professional scanner: Misfire Monitor / Live Data — While driving under various load conditions, a technician can watch the live misfire count for each cylinder. This helps confirm if the misfire on cylinder 6 happens only at idle, under acceleration, or during a cold start, which helps narrow down the cause (e.g., cold start misfires point to TSB software updates).

Wiring & Ground Locations

• Cylinder 6 Ignition Coil Control Wire — On a 5.7L HEMI PCM, this is often on connector C1551E, pin 73. The wire color is typically Violet with a Brown stripe.. If the ignition coil and spark plug are good, a technician must test this wire. A constant ground on this wire with the PCM disconnected indicates a short to ground in the harness. If the wire only becomes grounded when the PCM is connected, it could indicate a rare failure of the coil driver inside the PCM itself.
• Cylinder 6 Fuel Injector Control Wire — In a wiring diagram for a 2017 5.7L Ram (which is often similar to later models), the control wire for injector #6 is listed as pin 80 (K16) at the PCM connector.. Similar to the coil, this wire must be tested for continuity and shorts if the injector itself is known to be good. A break or short in this wire between the PCM and the injector will prevent it from firing and cause a P0306.

Real Owner Repair Stories

• Reddit user in r/Ram1500 (2019 Ram 1500 HEMI, 35k miles) — P0306 - Cylinder 6 Misfire code appeared.
  ❌ Tried (didn't work) One Ram dealer charged a $210 diagnostic fee, could not find the cause, and quoted $1800+ for an engine teardown, suspecting an internal problem.
  ✅ What actually fixed it A second opinion at another Ram dealer correctly diagnosed the problem as a faulty fuel injector, which was replaced and solved the issue.
• DodgeForum.com user (2010 Ram 1500 5.7L HEMI) — After replacing a bad camshaft and lifters for a misfire on cylinder #1, a new P0306 code appeared for cylinder #6 at idle only.
  ❌ Tried (didn't work) Changing spark plugs, Changing ignition coil, Checking wiring
  ✅ What actually fixed it The user eventually revealed the cause was a misaligned exhaust rocker arm on cylinder #4 that was caught under the rocker shaft bolt's washer during reassembly. While the code was for cylinder 6, the mechanical imbalance from the rocker issue on another cylinder was likely being misinterpreted by the PCM as a cylinder 6 misfire at idle. This highlights how mechanical issues can sometimes lead to misleading codes.

When the Usual Fixes Don't Work

• In one case involving a 2019 Ram 1500 with a P0306, the first dealership was unable to diagnose the problem after charging a diagnostic fee and recommended a costly engine teardown, suspecting a major internal failure. The owner sought a second opinion, and the other dealership correctly identified the root cause as a simple faulty fuel injector. This demonstrates that even with a code as specific as P0306, misdiagnosis is possible, and it's not always the most common or most severe potential cause.

OEM Part Supersession History

• 5038785AA, 5038785AB, 5038785AC → 5038785AD — These are part numbers for the 5.7L HEMI MDS lifters. The needle bearings in the roller were a known weak point, and later revisions aim to improve durability.
  Heads up: When replacing a failed MDS lifter, it is critical to also replace the camshaft if its corresponding lobe shows any signs of scoring or wear. Installing a new lifter on a damaged camshaft will cause the new lifter to fail very quickly.
• 56029129AA, 56029129AB, 56029129AF, 68060346AA → 68238603AA — Standard part evolution for the ignition coil used on the 5.7L HEMI engine, likely for improved reliability or manufacturing updates.

Model Year Variations Within This Range

• 2021-2024: The 3.6L Pentastar V6 and 5.7L HEMI V8 (with and without eTorque) were the primary engine options. The 3.0L EcoDiesel was phased out early in this period.
• 2025: For the 2025 model year, Ram discontinued the 5.7L HEMI V8. The new primary engine is the 3.0L 'Hurricane' twin-turbo inline-6. The 3.6L Pentastar V6 remains the base engine. Therefore, HEMI-specific issues like MDS lifter failure are not applicable to 2025+ models equipped with the Hurricane engine.