P0300 on 2020-2023 Ram ProMaster: Random Misfire Causes and Fixes

What's Unique About the 2020-2023 Ram PROMASTER

The Ram ProMaster in this year range uses the 3.6L Pentastar V6 engine. While many vehicles can get a P0300 code from simple tune-up parts, the Pentastar engine has a more complex and documented history. A common failure pattern involves the rocker arm bearings seizing, which then causes the camshaft lobe to wear down, a condition often preceded by an audible ticking sound. A specific Technical Service Bulletin (TSB #9100143) points to a potential issue with the right intake camshaft on the Pentastar Upgrade (PSU) engine, which can be the root cause of the P0300 code, making it critical to look beyond just spark plugs.

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 shaking idle
• Hesitation or stumbling during acceleration
• Flashing Check Engine Light
• Reduced engine power
• Poor fuel economy
• Difficulty starting the engine
• Audible ticking or tapping noise from the top of the engine (the 'Pentastar Tick'), especially on cold starts

Most Likely Causes

1. Worn Spark Plugs 🔴 High Probability Spark plugs are a standard maintenance item and a frequent cause of misfires on all gasoline engines.
   How to confirm: Remove the spark plugs and inspect for wear, fouling, or an incorrect gap. The plugs for the rear bank (cylinders 1, 3, 5) are under the intake manifold, requiring its removal, which is a 2-3 hour job.
   Typical fix: Replace all six spark plugs. It is recommended to use high-quality Iridium plugs like NGK or Champion. Also replace the upper intake manifold gaskets since the manifold must be removed.
   Est. part cost: $60-$150
2. Faulty Ignition Coils 🔴 High Probability Ignition coils are a common failure point that leads to weak or no spark. The rear bank (1, 3, 5) is located under the intake manifold, making replacement more labor-intensive.
   How to confirm: A diagnostic scan tool may show misfire counts per cylinder. A common technique is to swap a suspected coil with one from a known good cylinder to see if the misfire code changes (e.g., from P0301 to P0302). This is more difficult with a P0300 code unless you can identify specific misfiring cylinders via live data. 🎬 Watch: Advanced diagnostic tools for finding Pentastar engine misfires.
   Typical fix: Replace the faulty ignition coil(s). It is often recommended to replace all three coils on the bank under the intake manifold at once to avoid repeat labor costs.
   Est. part cost: $40-$80 per coil
3. Faulty Right Intake Camshaft and/or Rocker Arms 🟡 Medium Probability A specific TSB (#9100143) was issued for the Pentastar Upgrade (PSU) engine, indicating that a P0300 code can be caused by an issue with the right intake camshaft. This is often caused by failed rocker arm bearings, which seize and grind down the camshaft lobe. This is a widely documented issue known as the 'Pentastar Tick'.
   How to confirm: This is a complex diagnosis. A primary symptom is a persistent ticking noise from the valvetrain. Diagnosis involves removing the valve cover to inspect the camshaft lobes and rocker arms for visible wear and scoring after basic ignition and fuel issues have been ruled out.
   Typical fix: Replace the right intake camshaft (current PN 5047913AC or 5047913AD) and all intake rocker arms in that cylinder head, as per TSB #9100143. It is critical to replace the rocker arms as they are the root cause of the camshaft failure. 🎬 Watch: Full walkthrough of intake removal and rocker arm replacement.
   Est. part cost: $300-$500
4. Vacuum Leak 🟡 Medium Probability Leaks in the intake manifold gaskets or various vacuum hoses can introduce unmetered air, leading to a lean air-fuel mixture and random misfires.
   How to confirm: Perform a smoke test by introducing smoke into the intake system and watching for leaks. Spraying carburetor cleaner around suspected areas while the engine is running and listening for a change in idle speed is another method. The intake manifold gaskets are a common point of failure.
   Typical fix: Replace the leaking gasket or hose.
   Est. part cost: $20-$200
5. Fuel Delivery Issues ⚪ Low Probability A weak fuel pump or clogged fuel injectors can cause a lean condition and misfires across multiple cylinders.
   How to confirm: Check fuel pressure using a fuel pressure gauge connected to the fuel rail to ensure it's within spec. Test injector flow and spray pattern.
   Typical fix: Replace the weak fuel pump or clean/replace the faulty fuel injectors.
   Est. part cost: $100-$500

Rare But Worth Checking

• Faulty Crankshaft Position Sensor: TSB #S2008000191 specifically links P0300 with P1300 (Crankshaft Position Learn Out of Range), suggesting a potential issue with the sensor or its learned values. A relearn procedure may be necessary after sensor replacement.
• Low Engine Compression: Internal engine problems like worn piston rings, leaking valves, or a bad head gasket can cause low compression and misfires. This is a serious issue and should be investigated with a compression test and cylinder leak-down test if other causes are ruled out.

Diagnosis Steps

1. Scan the PCM for any other stored trouble codes. Pay close attention to cylinder-specific misfire codes (P0301-P0306) or codes related to fuel trim (P0171/P0174) or sensors.
2. Using a scan tool with live data, monitor the misfire counters for each cylinder to see if the random misfires are more frequent on certain cylinders or one bank.
3. Listen for an audible ticking noise from the engine, especially on a cold start. A distinct 'Pentastar Tick' strongly suggests a valvetrain issue (rocker arms/camshaft).
4. Inspect and replace spark plugs. This is a fundamental tune-up step. Be prepared for the 2-3 hour job of removing the upper intake manifold to access the rear bank (cylinders 1, 3, 5).
5. Inspect ignition coils. If a specific cylinder is misfiring more than others, swap its coil with a known good cylinder's coil and see if the misfire follows.
6. Perform a smoke test to check for vacuum leaks, especially around the intake manifold gaskets and vacuum hoses.
7. Check fuel pressure to rule out a weak fuel pump.
8. If the above steps do not resolve the issue and/or a ticking noise is present, the diagnosis should proceed to the more complex, vehicle-specific causes. Remove the valve cover(s) and inspect the camshaft lobes and rocker arms for wear, scoring, or seized bearings as indicated by TSB #9100143.
9. Check the crankshaft position sensor and perform a relearn procedure if necessary, especially if code P1300 is present.

Parts You'll Likely Need

• Spark Plugs (OEM #SP142582AC) — Standard maintenance item and the most frequent cause of engine misfires.
  Trusted brands: NGK, Champion
  OEM price range: $100-$180
  Aftermarket price range: $60-$150
• Ignition Coil (OEM #05149199AA) — A common failure point causing a lack of spark to the cylinder.
  Trusted brands: Mopar, Bosch, Delphi
  OEM price range: $60-$100
  Aftermarket price range: $40-$80
• Right Intake Camshaft (OEM #5047913AC) — A documented cause of P0300 on the 3.6L Pentastar Upgrade engine, as cited in TSB #9100143. Part number 5047913AC supersedes the older 05047913AB.
  Trusted brands: Mopar
  OEM price range: $250-$450
  Aftermarket price range: $200-$350
• Intake Manifold Gasket Set (OEM #5184331AC) — Required when removing the intake manifold to access the rear bank of spark plugs, coils, or for valvetrain work.
  Trusted brands: Mopar, Fel-Pro, Mahle
  OEM price range: $30-$60
  Aftermarket price range: $20-$40
• Rocker Arm (OEM #5184296AH) — The root cause of camshaft failure. Failed rocker arm bearings seize and destroy the cam lobe. It is critical to replace all rocker arms on the affected head when replacing a camshaft.
  Trusted brands: Mopar, Mahle
  OEM price range: $10-$20 per arm
  Aftermarket price range: $8-$15 per arm

Related Codes That Often Appear With This One

• P0301, P0302, P0303, P0304, P0305, P0306 — These codes indicate a misfire on a specific cylinder. They often appear alongside P0300 as the PCM tries to narrow down the random misfire issue.
• P1300 — As per TSB #S2008000191, this code for 'Crankshaft Position Learn Out of Range' can be directly associated with the P0300 misfire code on this vehicle.
• P0171 / P0174 — These codes indicate a 'System Too Lean' condition on Bank 1 and Bank 2, which is a common cause of random misfires due to issues like vacuum leaks or a weak fuel pump.

Technical Service Bulletins (TSBs) & Recalls

• 9100143: Addresses a P0300 code caused by the right intake camshaft on the Pentastar Upgrade Engine.
• S2008000191: Links the P0300 misfire code with a P1300 crankshaft position sensor code.

Platform-Specific Known Issues

• Cylinder #2 Spark Plug Tube Corrosion: Due to the ProMaster's engine bay design, which lacks a plastic engine cover, water from the cowl can drip directly onto the #2 cylinder area. This can cause the spark plug tube to rust and corrode, leading to the spark grounding out against the tube wall and causing a P0302 misfire, which can sometimes contribute to a P0300. The fix involves thoroughly cleaning the tube and applying a generous amount of dielectric grease to the new coil boot.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Resistance — expected: 0.4 to 2.0 ohms. Failure: A reading outside this range indicates a faulty coil winding.
• Ignition Coil Secondary Resistance — expected: 6,000 to 10,000 ohms. Failure: A reading outside this range suggests the coil cannot produce a strong enough spark.
• Fuel Pressure — expected: Must be checked against manufacturer specification for the specific model year.. Failure: Pressure below the specified range indicates a weak fuel pump or clogged filter, causing a lean condition and misfires.

Hidden / Shadow Codes Worth Checking

• Mode 6 Misfire Counters: This is not a trouble code, but a function within an advanced scan tool. It displays the raw number of misfire events counted by the PCM for each individual cylinder, even if the count is not high enough to trigger a specific P0301-P0306 code. This is extremely valuable for a P0300 as it helps pinpoint which cylinders are the primary offenders. (see via An advanced OBD-II scanner with Mode 6 capability or the dealer-level wiTECH tool.)

Scan Tool Commands That Help

• wiTECH or advanced bidirectional scanner: Crankshaft Position Relearn — This procedure is required after replacing the crankshaft position sensor or flexplate. It may also be necessary after major engine work. TSB #S2008000191 links P0300 with P1300 (Crankshaft Position Learn Out of Range), making this a critical step if P1300 is present.
• wiTECH or advanced bidirectional scanner: ASD Relay Actuation — To test the power supply circuit to the ignition coils. A technician can command the Auto Shutdown (ASD) relay 'on' with the engine off and then use a test light to verify voltage at the ignition coil harness connector, ruling out a wiring issue.
• wiTECH or advanced bidirectional scanner: Injector Kill / Misfire Counter Analysis — While watching live misfire data, a technician can disable one fuel injector at a time. If disabling an injector causes no change in idle quality or misfire count, it confirms that cylinder was not contributing, pointing to a problem with that specific cylinder's ignition, fuel, or compression.

Wiring & Ground Locations

• Ignition Coil Connector — On top of each ignition coil, connected to the engine wiring harness.. This 2-pin connector is where the coil receives power and its firing signal. Pin 1 is the ASD Relay Output (12V+ power) and Pin 2 is the Coil Control circuit, which is pulsed to ground by the PCM to fire the coil. Testing for 12V power and a pulsing ground signal at this connector can quickly determine if the coil itself or the wiring/PCM is at fault.
• Main Engine Ground — A heavy gauge wire connecting the engine block to the vehicle's chassis/frame.. A loose or corroded main engine ground can cause a weak or inconsistent spark across all cylinders, leading to random misfires. While not specific to P0300, it's a fundamental check for any widespread electrical issue.

Real Owner Repair Stories

• YouTube channel 'TDR Auto' (2015 Jeep Wrangler 3.6L Pentastar (same engine family)) — Consistent misfire on cylinder 3, check engine light on.
  ❌ Tried (didn't work) Replaced fuel injector, spark plug, and ignition coil., A previous shop misdiagnosed it as a burnt valve requiring a cylinder head job.
  ✅ What actually fixed it The technician identified a failed rocker arm bearing on cylinder 3. The needle bearings had collapsed, causing excessive play. The rocker arm was replaced, and a cylinder leak-down test confirmed the cylinder head and valves were fine. This caught the failure before the cam lobe was destroyed.
• Reddit user in r/MechanicAdvice (2013 Jeep Wrangler 3.6L Pentastar (same engine family)) — After replacing a camshaft, all rocker arms, and lifters, the engine started but threw a P0300 code, ran rich, and would stall after 10 seconds.
  ❌ Tried (didn't work) The user stated that the valve timing was set perfectly.
  ✅ What actually fixed it The user did not post the final resolution, but the symptoms strongly point to an issue created during reassembly. The most likely causes are incorrect valve timing despite the user's belief, or a failure to perform a required sensor relearn procedure (like the crankshaft position sensor relearn) after the major mechanical work.

"I Checked Everything" — The Actual Cause

• While not specific to the 3.6L ProMaster, a well-documented pattern on other Stellantis engines (like the 2.4L in the ProMaster City) is a P0300 code where a smoke test reveals no vacuum leaks. The actual cause was an internally failed PCV valve, which is integrated into the valve cover. This creates a vacuum leak internal to the crankcase system that a smoke test at the intake manifold may not detect, but still leans out the air-fuel mixture enough to cause random misfires. The only fix is replacing the entire valve cover assembly.

OEM Part Supersession History

• 05047913AA, 05047913AB → 5047913AC, which was then superseded by 5047913AD — Revisions to address the wear caused by failing rocker arms. The TSB specifically mentions replacing older 'AA' or 'AB' versions.
  Heads up: Using an old-stock 'AA' or 'AB' part will likely lead to a repeat failure. It is critical to use the latest available part number (currently 5047913AD) when performing the repair.

Model Year Variations Within This Range

• 2022-2023: Starting in 2022, the ProMaster received the 'Pentastar Upgrade' (PUG) engine and a new transmission. Key engine changes include a higher compression ratio (11.3:1 vs. 10.2:1), the addition of an external cooled EGR valve (previously handled by cam phasing), and slightly different power ratings (276 hp vs. 280 hp). The transmission was changed from the 6-speed 62TE to the 9-speed 948TE automatic. These changes mean some sensors, the ECU software, and transmission-related diagnostics are different from the 2020-2021 models.