P0306 on 2015-2020 Ram 2500: Cylinder 6 Misfire Causes and Fixes

What's Unique About the 2015-2020 Ram 2500

For the 2015-2020 Ram 2500, the cause of a P0306 code is entirely dependent on the engine. The 6.4L HEMI V8 (gas) most often has ignition-related misfires, but this code can also be the first sign of a serious internal engine problem known as the 'HEMI tick,' caused by a failed lifter damaging the camshaft. In contrast, on the 6.7L Cummins (diesel), a single-cylinder misfire code almost exclusively points to a problem with the high-pressure fuel system, with the fuel injector for cylinder 6 being the primary suspect.

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 fifth-gen trucks feature a redesigned frame, new interior tech, and made the 6.4L HEMI the standard gas engine. While the core engines are similar, some electronics, part numbers, and fuel systems (like the failure-prone Bosch CP4.2 pump on 2019-2020 Cummins) differ.

Symptoms You May Notice

• Rough or shaking idle
• Noticeable loss of power and acceleration
• Hesitation or stumbling during acceleration
• Flashing Check Engine Light (indicates a severe misfire)
• Reduced fuel economy
• Engine knocking or ticking sounds, particularly a rhythmic tick that increases with RPM on HEMI engines.
• Excessive white or blue-white smoke from the exhaust, especially at idle (more common on Cummins).
• Fuel smell from the exhaust.

Most Likely Causes

1. Failed Ignition Coil (6.4L HEMI V8 Only) 🔴 High Probability → Shop Ignition Coil Coil-on-plug systems are common failure points due to constant exposure to high engine heat and vibration, causing the internal windings to break down over time.
   How to confirm: Cylinder 6 on the 6.4L HEMI is the third cylinder from the front on the passenger's side (Bank 2). Swap the ignition coil from cylinder 6 with another cylinder (e.g., cylinder 4, the second cylinder on the same bank). Clear the codes and drive. If the code changes to P0304, the coil is faulty. This is a definitive and free diagnostic step.
   Typical fix: Replace the faulty ignition coil. The OEM Mopar part number is 68238603AA. It's often wise to replace the spark plugs at the same time.
   Est. part cost: $50 - $90 for one genuine Mopar coil.
2. Worn Spark Plugs (6.4L HEMI V8 Only) 🔴 High Probability → Shop Spark Plug The 6.4L HEMI uses two spark plugs per cylinder (16 total), increasing the statistical chance of a single plug failing or fouling compared to a single-plug design.
   How to confirm: After ruling out the coil, remove both spark plugs from cylinder 6. Inspect for a worn electrode, cracks in the porcelain, or heavy black/oily deposits. A fuel-soaked plug indicates it is not firing.
   Typical fix: Replace the spark plugs in cylinder 6. It is best practice to replace all 16 spark plugs as a set to ensure consistent performance and avoid future misfires.
   Est. part cost: $5 - $15 per plug.
3. Failed Fuel Injector (6.7L I6 Cummins Diesel Only) 🔴 High Probability → Shop Fuel Injector The high-pressure common rail fuel system operates at extreme pressures (over 20,000 psi), which puts significant stress on injectors, making them a common wear item and the number one cause of single-cylinder misfires on this engine.
   How to confirm: A 'cylinder contribution test' or 'injector cut-out test' using a professional-grade scan tool is the most accurate method. This test deactivates each injector one by one to see which one causes the least change in engine RPM, identifying the weak cylinder. A bent push tube can also be a sign of internal issues related to a misfire.
   Typical fix: Replace the faulty fuel injector and the high-pressure connector tube. The connector tube is considered a one-time-use part and is critical for a proper seal. After installation, the new injector's IQA code must be programmed into the PCM. The OEM Bosch part number for a new injector for 2013-2018 models is 0445120342 (Mopar R8210512AA).
   Est. part cost: $400 - $650 for a single new Bosch injector, or around $300-$450 for a remanufactured one.
4. Camshaft and Lifter Failure (6.4L HEMI V8 Only) 🟡 Medium Probability → Shop Engine Camshaft These engines are known for a specific valvetrain issue where the needle bearings in a lifter's roller fail. The roller stops spinning and grinds against the camshaft, flattening the lobe and preventing the valve from opening fully, which causes a persistent misfire. This is often called the 'HEMI tick' and is a well-documented problem on owner forums.
   How to confirm: Listen for a loud, rhythmic ticking noise that increases with engine RPM. A definitive diagnosis requires removing the valve cover to inspect the valvetrain or finding metal shavings ('glitter') in the engine oil and filter. A user on a Reddit forum described chasing a P0306 by swapping coils and injectors before realizing it was a mechanical issue.
   Typical fix: This is a major engine repair requiring replacement of the camshaft, all lifters, head gaskets, and other related components. The oil system must be thoroughly flushed to remove metal debris.
   Est. part cost: $1,000 - $2,500+ for a cam and lifter kit. Labor is extensive and can bring the total repair cost to over $5,000.

Rare But Worth Checking

• PCM Software Issue: Multiple Technical Service Bulletins, including #18-102-22 REV A and its successor #18-067-23, list P0301-P0306 misfire codes as a condition that may be resolved with a PCM software update, particularly on 2020 Cummins models.
• Low Engine Compression: If ignition and fuel system checks don't reveal the problem, a mechanical issue could be the cause. A burnt valve, worn piston rings, or a leaking head gasket can cause a loss of compression, leading to a misfire. A compression test is required to diagnose this.
• High-Pressure Fuel Pump (HPFP) Failure (2019-2020 Cummins): A known issue on 2019-2020 models involves the Bosch CP4.2 HPFP failing and sending metal debris through the entire fuel system, destroying the injectors. This led to recall Y78 (NHTSA 21V880). While it often triggers low fuel pressure codes like P0087, it can also cause multiple misfire codes (P0300-P0306) as the injectors fail.
• Injector Wiring Harness: The wiring harness or electrical connector to the fuel injector can become damaged or loose, causing an intermittent connection and a misfire. This can be diagnosed by checking for a steady pulse signal at the injector connector with a noid light and inspecting the harness for chafing or corrosion.

Diagnosis Steps

1. Identify your engine: 6.4L HEMI (gas) or 6.7L Cummins (diesel). The diagnostic path is completely different.
2. For 6.4L HEMI:
3. a. Locate cylinder 6, which is the third cylinder back from the front on the passenger's side.
4. b. Swap the ignition coil from cylinder 6 with another cylinder (e.g., cylinder 4). Clear the codes. If the misfire code moves to the new cylinder (e.g., P0304), the coil is bad and needs replacement.
5. c. If the code remains P0306, inspect the two spark plugs in cylinder 6 for wear, fouling, or damage. Replace if necessary.
6. d. Listen carefully for a loud, rhythmic ticking noise that gets faster with engine RPM. If present, suspect a camshaft/lifter issue and inspect the engine oil for metal shavings, especially when changing the oil filter.
7. e. If the above steps don't find the cause, check the fuel injector wiring for a pulse using a noid light and inspect the harness for damage.
8. f. As a final step, perform a compression test to check for mechanical engine problems like a bad valve or piston rings.
9. For 6.7L Cummins:
10. a. The most reliable first step is to use a high-quality scan tool to perform a 'cylinder contribution test' to confirm cylinder 6 is underperforming.
11. b. Inspect the wiring harness and electrical connector going to the cylinder 6 fuel injector for any visible damage, corrosion, or looseness.
12. c. For 2019-2020 models, check your VIN for recall Y78 regarding the CP4.2 fuel pump. Check the fuel filter for metallic 'glitter' which is a definitive sign of CP4 failure.
13. d. Check with a dealer for any available PCM software updates, as TSBs #18-102-22 REV A and #18-067-23 indicate updates can resolve false misfire codes on 2020 models.
14. e. If no other issues are found, the fuel injector is the most likely cause. Replacement requires special tools and programming the new injector's IQA code into the PCM.

Parts You'll Likely Need

• Ignition Coil (HEMI Only) — This is the most common cause of a single-cylinder misfire on the 6.4L HEMI engine due to failure from heat and vibration.
  Trusted brands: Mopar, NGK, Denso
  OEM price range: $70-$120
  Aftermarket price range: $40-$80
• Spark Plugs (HEMI Only) (OEM #SP138239AC) — A routine wear item. With 16 plugs in the engine, the chance of one failing is relatively high. They should be replaced if a coil is bad or if they are near their service interval.
  Trusted brands: NGK, Champion
  OEM price range: $10-$20 per plug
  Aftermarket price range: $5-$15 per plug
• Fuel Injector (Cummins Diesel) — The most common cause of a P0306 code on the 6.7L Cummins. The high-pressure fuel system puts immense stress on these components, making them a primary failure point.
  Trusted brands: Bosch, Mopar
  OEM price range: $500-$800+ (Remanufactured)
  Aftermarket price range: $300-$600 (Remanufactured)
• Camshaft and Lifter Kit (HEMI Only) — Required for the known 'HEMI tick' issue. If a lifter fails, it destroys the camshaft, and both must be replaced along with related gaskets and seals.
  Trusted brands: Mopar, Comp Cams
  OEM price range: $1500-$2500
  Aftermarket price range: $1000-$1800

Related Codes That Often Appear With This One

• P0300 — If you see a P0300 (Random/Multiple Cylinder Misfire) code, it means the issue is affecting more than just cylinder 6. This points towards a systemic problem like a vacuum leak, contaminated fuel, or a failing HPFP on Cummins models.
• P0206 — This code indicates a malfunction in the cylinder 6 fuel injector circuit. If you see P0206 with P0306, it strongly suggests the fuel injector or its wiring is the root cause, making diagnosis much more direct.
• P0087 — On 2019-2020 Cummins models, P0087 (Fuel Rail/System Pressure - Too Low) seen with misfire codes is a strong indicator of a failing CP4.2 high-pressure fuel pump.

Technical Service Bulletins (TSBs) & Recalls

• 1810222REVA (superseded by 18-067-23): For 2020 Cummins models, lists P0301-P0306 misfires as a condition that may be resolved with a PCM software update.
• 1806623: Lists P0301-P0306 for 2019 models as part of a PCM update.
• 1810722REVA: Lists P0301-P0308 for 2015 models as part of a PCM update.
• Recall Y78 / NHTSA 21V880: For 2019-2020 Cummins models, recalls the Bosch CP4.2 high-pressure fuel pump which can fail and cause fuel starvation and misfires.

Platform-Specific Known Issues

• Camshaft/Lifter Failure ('HEMI Tick'): → Shop Engine Camshaft A significant known issue is the failure of the roller lifters, which stop rotating and grind down the camshaft lobes. This causes a persistent misfire (like P0306) accompanied by a distinct ticking sound. It is a major and expensive engine repair.
• Bosch CP4.2 High-Pressure Fuel Pump Failure: These model years were equipped with a CP4.2 pump that is prone to catastrophic failure, sending metal debris throughout the entire fuel system. This is the subject of safety recall Y78 / NHTSA 21V880. It can cause multiple DTCs, including misfires and P0087 (low fuel rail pressure).

Mechanic-Grade Diagnostic Values

• 6.4L HEMI Fuel Injector Resistance — expected: 11-15 Ohms. Failure: A reading significantly outside this range, or an infinite (OL) reading, points to a failed injector coil.
• 6.7L Cummins Fuel Injector Resistance — expected: 0-1 Ohm. Failure: A reading of infinite resistance (OL) indicates an open coil in the injector.
• 6.4L HEMI Ignition Coil Primary Resistance — expected: ~0.4 - 0.5 Ohms. Failure: A reading outside of the specified range indicates a faulty coil.
• 6.7L Cummins Low-Pressure Fuel System (Lift Pump) — expected: 10-15 PSI at idle. Failure: Pressure dropping near or to zero PSI under load indicates a weak lift pump or clogged fuel filter.
• 6.7L Cummins High-Pressure Fuel Rail (Cranking) — expected: ~4,000 PSI. Failure: Significantly lower pressure while cranking suggests leaking injectors or a weak high-pressure pump.
• 6.7L Cummins Injector Balance Rates (Scan Tool) — expected: Within ±2.0 mm³ at warm idle. Failure: Consistent readings beyond ±4.0 mm³ suggest a faulty injector or a mechanical cylinder issue.
• 6.7L Cummins Injector Return Flow Test (Total) — expected: Maximum of 210 mL in 30 seconds for all injectors combined. Failure: Any single injector contributing more than 40 mL of the total is considered to have excessive leakage and is faulty.

Hidden / Shadow Codes Worth Checking

• Mode 6 Misfire Counters: Most advanced scan tools can access Mode 6 data, which includes non-continuous monitor test results. For misfires, you can view raw misfire counts per cylinder for the current and last 10 driving cycles. This can confirm that cylinder 6 is the primary or only source of misfires, even if they aren't always frequent enough to keep the CEL on. (see via Professional-grade scan tool with Mode 6 data stream capabilities.)

Scan Tool Commands That Help

• wiTECH, Autel, Snap-on, AlfaOBD: Injector Kill / Cylinder Contribution Test — This is a primary diagnostic step for the 6.7L Cummins. It allows you to disable injectors one by one. If disabling cylinder 6 causes no change in idle quality, it confirms that cylinder is not contributing (misfiring), strongly pointing to a fuel injector or mechanical issue.
• wiTECH, Autel, Snap-on, AlfaOBD: Injector Quantity Adjustment (IQA) / Trim Code Programming — This function is required *after* replacing a fuel injector on a 6.7L Cummins engine. Each new injector has a unique calibration code that must be programmed into the ECM to ensure correct fuel metering and smooth engine operation.
• wiTECH (Dealer), high-end scan tools: Fuel Pressure Override Test — For advanced diagnostics on a 6.7L Cummins, this commands the fuel pump to a specific high pressure (e.g., 26,107 PSI) to perform a controlled leak-down or return flow test, which is the most accurate way to identify leaking injectors.

Real Owner Repair Stories

• Reddit user in /r/MechanicAdvice (2015 Ram 1500 5.7L HEMI with ~150k miles) — P0306 (Cylinder 6 Misfire) appeared a few days after a spark plug change. Check engine light would come on, turn off, and sometimes flash.
  ❌ Tried (didn't work) Cleared the code, but it returned., Swapped the ignition coil from cylinder #6 to cylinder #4. The P0306 code remained, ruling out the coil.
  ✅ What actually fixed it The user planned to swap the spark plugs next, then the fuel injector, to see if the misfire code would follow the part to the new cylinder. This systematic swapping process is the correct diagnostic path for this engine.
• RamForum.com user (2015 Ram HEMI with 36k miles) — Check engine light with code P0306 appeared after a remote start.
  ✅ What actually fixed it The user cleared the code and it did not immediately return. This suggests a potential intermittent or 'fluke' misfire, possibly related to cold start conditions, which is a known issue that can sometimes be resolved by a PCM software update.

OEM Part Supersession History

• 56029129AA, 56029129AB, 56029129AF, 68060346AA → 68238603AA — Standard part evolution for improved reliability or manufacturing changes.

Model Year Variations Within This Range

• 2019-2020 (6.7L Cummins): These model years used the Bosch CP4.2 high-pressure fuel pump, which is known to fail and contaminate the entire fuel system. A P0306 code on these trucks, especially if accompanied by a P0087 (low fuel rail pressure), warrants an immediate check of the fuel filter for metal debris before replacing any injectors.
• 2013-2018 (6.7L Cummins): According to some sources, unlike earlier models, replacement fuel injectors for 2013-2018 trucks do not require IQA/trim code programming into the ECM after installation. However, other sources state it is required for all common rail Cummins, so it is best practice to perform this step.