P0604 on 2014-2020 Ram 3500: Internal RAM Error Causes and Fixes

What's Unique About the 2014-2020 Ram 3500

For this specific generation range of Ram 3500, particularly those with the 6.7L Cummins engine, the P0604 code is uniquely and repeatedly tied to software issues. Ram has issued multiple Technical Service Bulletins (TSBs) confirming that this code often appears alongside other faults (especially emissions-related codes like P2201 and P20EE) and that the official fix is a PCM software update, not a hardware replacement. Some of these updates were specifically designed to change the fault logic from a one-trip to a two-trip fault to prevent unnecessary check engine light illumination. TSB #18-002-14 REV. B even notes that P0604 can be set on 2014 models simply by enabling the remote throttle feature, with the fix being a PCM reflash. This is different from many other vehicles where a P0604 code more directly points to a failed computer.

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 end of the fourth generation (2014-2018) and the start of the fifth generation (2019-2020). The issue of software causing this code is well-documented for both generations, with many TSBs focused on the 2014-2018 models, but the principle applies to both.

Symptoms You May Notice

• Check Engine Light is on
• Engine may stall, hesitate, or run rough
• Harsh or erratic transmission shifting
• Vehicle may not start or may be hard to start
• Failed emissions test
• ABS or Traction Control light may illuminate.
• "Service Electronic Throttle Control" message may appear, especially on 2014 models.

Most Likely Causes

1. Powertrain Control Module (PCM) Software Glitch 🔴 High Probability Manufacturer TSBs #18-044-26, #1806623, and others confirm that updated software is the prescribed fix for this code when it appears with other performance issues. TSB #18-002-14 REV. B specifically links P0604 to enabling the remote throttle feature on 2014 models, reinforcing the software connection.
   How to confirm: A Ram dealer or a qualified shop with a wiTECH scan tool can check your vehicle's calibration ID against the latest available software version from the manufacturer.
   Typical fix: Reprogramming (flashing) the PCM with the latest manufacturer software. This typically takes about one hour of labor.
   Est. part cost: $0
2. Low Battery Voltage or Weak Batteries 🟡 Medium Probability These trucks, especially with the Cummins engine, have a dual-battery system. They are highly sensitive to voltage, and a drop during the grid heater cycle or startup can cause the PCM's self-test to fail and corrupt its RAM, triggering the code.
   How to confirm: Test both batteries individually under load. 🎬 See how to load test Cummins batteries using the starter. Voltage should be above 12.4V at rest and should not drop below 9.6V during cranking. Check the charging system output to ensure it's stable and between 13.5 and 14.8 volts. Inspect all battery terminals and primary engine/body ground straps for corrosion or looseness.
   Typical fix: Replace weak or failing batteries (always replace as a pair on a dual-battery system). Clean or tighten all battery terminals and ground straps.
   Est. part cost: $200-$500 for two batteries
3. Failing Powertrain Control Module (PCM) ⚪ Low Probability While possible, actual hardware failure is less common than software or voltage issues on this platform. A burnt smell near the computer can be an indicator of hardware failure.
   How to confirm: This is a diagnosis of exclusion. If software is up to date, both batteries are new and healthy, the charging system is stable, and all power and ground circuits to the PCM test perfectly, the module itself is suspect.
   Typical fix: Replace the PCM. This requires programming the new module to the vehicle's VIN and security information.
   Est. part cost: $800-$1800

Rare But Worth Checking

• Faulty Aftermarket Tuner/Programmer: If you have an aftermarket performance tuner, it may have corrupted the PCM's software. Removing the tuner and flashing the PCM back to stock is a necessary diagnostic step.
• Poor PCM Power or Ground Connections: Corroded or loose wiring at the PCM connector can cause intermittent voltage drops, leading to this code. A voltage drop test on the power and ground circuits can identify this. Resistance on ground circuits should be below 0.1 Ω.
• Failing Alternator: An alternator producing voltage spikes, excessive AC ripple, or simply undercharging can disrupt the PCM's sensitive electronics and corrupt its memory. The charging system should maintain a stable voltage, typically between 13.5-14.8V when running.
• Faulty Totally Integrated Power Module (TIPM): In some cases, the main fuse box (TIPM) can fail and cause voltage irregularities to the PCM, triggering a P0604 even when the PCM itself is good. This was the reported fix for at least one owner after a reflash and new batteries did not solve the issue.

Diagnosis Steps

1. Check for other DTCs. P0604 is often accompanied by other codes that can point to the root cause, especially if they are mentioned in a TSB (e.g., P20EE, P2201).
2. Check Battery Health and Connections: Load test both batteries individually. Ensure voltage is above 12.4V at rest and doesn't drop below 9.6V during cranking. Verify charging system voltage is stable and within the 13.5V-14.8V range. Ensure all terminals and ground straps are clean and tight.
3. Check for Available Software Updates: This is the most critical step. Have a Ram dealer or qualified shop use a wiTECH tool to check for PCM software updates (reflashes). This is the most common fix.
4. Remove Aftermarket Devices: If any aftermarket tuners or programmers are installed, remove them completely and return the PCM to its stock programming.
5. Inspect PCM Power and Ground Connections: Visually inspect the PCM connectors for corrosion or damage. Check the main engine and chassis ground straps for tightness and integrity.
6. Perform a Voltage Drop Test: If the code persists, perform a voltage drop test on the PCM's power and ground circuits to rule out wiring issues. Resistance should be below 0.1 Ω on ground circuits.
7. Condemn the PCM: If all previous steps pass and the code still returns immediately after being cleared, the PCM has likely failed internally and requires replacement.

Parts You'll Likely Need

• Powertrain Control Module (PCM) (OEM #Example for 2018: 68336278AA; Example for 2019-2020: 68363277AA (Part numbers are highly VIN-specific)) — This is the part that is replaced if software updates and electrical checks fail to resolve the internal RAM error.
  Trusted brands: Mopar (OEM)
  OEM price range: $1200-$1800
  Aftermarket price range: $800-$1200 (Remanufactured)
• PCM Software Update — This is a service, not a physical part. It is the most common and manufacturer-recommended solution for this code on this platform.
  Trusted brands: Ram/Mopar Dealer Service
  OEM price range: $150-$350 (Labor)
  Aftermarket price range: N/A

Related Codes That Often Appear With This One

• P0607 — This code for 'ECU Internal Performance' is also a generic PCM self-test failure code, often triggered by the same software or voltage issues. (Cited in TSB #1806623)
• P060C — This code for 'Internal Control Module Main Processor Performance' points to a related internal self-test failure. (Cited in TSB #18-044-26)
• P2201 — This NOx sensor code is mentioned alongside P0604 in multiple TSBs, suggesting a software update addresses both emissions and module performance logic. (Cited in TSB #1806623)
• P0868 — This code for 'Line Pressure Low' in the transmission is also listed in TSBs with P0604, indicating a software reflash can solve both engine and transmission control issues. (Cited in TSB #18-052-19 REV. A)
• P20EE — This NOx Catalyst Efficiency code is frequently mentioned with P0604 in the context of software updates, strongly suggesting the root cause is a PCM software glitch related to emissions monitoring.

Technical Service Bulletins (TSBs) & Recalls

• 18-044-26: Mentions P0604-00 as an Internal Control Module RAM error that can be stored.
• 1806623: Lists P0604-00 as a potential code that can be addressed by a PCM software update.
• 1810122REVA: Also lists P0604-00 in the context of a PCM software update.
• 18-052-19 REV. A: Includes P0604-00 as a code that may be resolved with a PCM reflash.
• 18-002-14 REV. B: Notes P0604 can be set on 2014 models when enabling the remote throttle feature, fixed by a reflash.

Platform-Specific Known Issues

• TSB #18-044-26 notes that P0604 can be set along with other codes and may be resolved by a software update.
• TSBs #1806623, #1810122REVA, and #18-052-19 REV. A all list P0604 as one of several codes that may be present due to software issues requiring a PCM reflash.
• TSB #18-002-14 REV. B specifically identifies that on 2014 models, enabling the remote throttle feature can trigger P0604, and the fix is a software update.

Mechanic-Grade Diagnostic Values

• PCM Ground Circuit Resistance — expected: Below 0.1 Ω. Failure: Resistance above 0.1 Ω indicates a poor ground connection that can cause voltage anomalies and trigger RAM errors.
• Voltage Drop on PCM Power/Ground Circuits — expected: Less than 0.2 Volts (200 millivolts) while cranking. Failure: A reading higher than 0.2V indicates excessive resistance in the wiring or connections between the battery and the PCM.
• Cranking Voltage at PCM Connector — expected: Should remain above 9.6 Volts. Failure: A drop below this threshold during engine cranking can corrupt the PCM's RAM self-test on startup.
• Charging System Voltage During PCM Reflash — expected: Stable between 13.2 and 13.5 volts. Failure: Voltage climbing above 13.5 volts during a reflash procedure can interrupt the process and corrupt the module.

Scan Tool Commands That Help

• wiTECH 2.0: Restore Vehicle Configuration — After replacing and programming a new PCM, this function is used to verify that all vehicle options and settings are correctly configured in the new module.
• wiTECH 2.0: Check PCM VIN — This is a mandatory step when installing a new or used PCM. The vehicle's VIN must be written to the module for it to communicate with other modules and for the immobilizer to function.
• wiTECH 2.0: PCM Reprogram/Reflash — This is the primary repair procedure when P0604 is caused by outdated software, as documented in multiple TSBs.

Wiring & Ground Locations

• Powertrain Control Module (PCM/ECM) — Mounted to the driver's side of the engine block, below the intake horn on 6.7L Cummins models.. This is the module setting the code. Its location makes it susceptible to heat and vibration, making secure connector and ground integrity critical.
• PCM Connector C2, Pins 4 & 6 — On the Powertrain Control Module itself.. These are primary ground circuit terminals for the PCM. A poor connection or high resistance at these specific pins can cause voltage instability within the module, mimicking an internal RAM failure and triggering P0604.
• Main Body Grounds (G301, G302) — Located on the left front body structure.. These are major chassis ground points. Corrosion or looseness here can affect multiple systems, including the stability of the power supplied to the PCM.

Real Owner Repair Stories

• HDrams.com user (2019 Ram 3500) — P0604 code present, vehicle experienced electrical issues.
  ❌ Tried (didn't work) Attempting to reconnect dangling ground cables near the passenger side battery caused sparking, indicating a short or incorrect connection point.
  ✅ What actually fixed it The user identified the loose cables as belonging to the grid heater relay. The final resolution was to have the dealer correctly re-attach the grounds to their proper location, which resolved the electrical issues.
• Forum user report (generic Ram) (2009 Ram 2500 6.7L Cummins) — On startup, voltage gauge drops to ~10V, 'check gauges' light comes on, and electronic throttle control warning light illuminates.
  ❌ Tried (didn't work) Replacing both batteries per dealer recommendation did not fix the problem.
  ✅ What actually fixed it The issue was traced to a poor connection or corrosion at the battery terminals or the main frame ground, which caused a significant voltage drop during the high-amperage draw of the grid heater and starter.

OEM Part Supersession History

• 68336278AA → This part number appears to be current for 2018 models with the 6.7L Cummins engine as of early 2026. No direct supersession was found, but it is sold as an unprogrammed module requiring dealer programming. — N/A
  Heads up: This part is listed for 2018 models and requires programming with the vehicle's VIN to function. It is not compatible with 2019+ models which use a different architecture.

Model Year Variations Within This Range

• 2019-2020: The 2019 model year marked the beginning of the 5th generation, which introduced significant changes, including a different frame, interior, and updated engine options. For gasoline engines, the 8-speed transmission became available, which affects PCM software and diagnostics compared to the 6-speed in the 2014-2018 models.
• 2014: TSB #18-002-14 REV. B specifically calls out 2014 models where enabling the 'remote throttle feature' could trigger a P0604 code, requiring a PCM software update to fix.