P0604 on 2017-2021 Chrysler Pacifica Hybrid: Internal RAM Error Causes and Fixes

What's Unique About the 2017-2021 Chrysler PACIFICA PLUG-IN HYBRID

While a P0604 code on many vehicles points directly to a failed and expensive Powertrain Control Module (PCM), the situation on the Pacifica Hybrid is unique. Chrysler issued a Technical Service Bulletin (TSB #18-044-26) that specifically identifies a software glitch as a primary cause for this code. This means a dealership software reflash is the correct first step, potentially saving owners the significant cost of unnecessarily replacing the PCM. This pattern of software-driven faults is common across modern Stellantis platforms.

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
• Engine may stall or not start.
• Intermittent loss of power or sudden shutdown while driving.
• Vehicle may enter a reduced-power 'limp mode'
• Problems with automatic transmission shifting, which may feel harsh or erratic.
• Failed emissions test due to OBD-II monitor issues.
• Anti-lock Brake System (ABS) or Traction Control light may illuminate.

Most Likely Causes

1. Outdated Powertrain Control Module (PCM) Software 🔴 High Probability → Shop Engine Control Module (ECM) Chrysler has identified a software issue that can incorrectly trigger this code, as documented in TSB #18-044-26. This is the most common cause for this specific vehicle.
   How to confirm: A technician at a Chrysler dealership can check the current software version of the PCM using the wiTECH scan tool and compare it against the latest version available.
   Typical fix: Update the PCM software using a factory-approved scan tool. This procedure is often called a 'reflash' and typically costs 1-1.5 hours of shop labor.
   Est. part cost: $0
2. Faulty Powertrain Control Module (PCM) 🟡 Medium Probability → Shop Engine Control Module (ECM)
   How to confirm: This is diagnosed by exclusion. If a software update does not resolve the code and all power/ground connections and 12V battery voltage are verified to be good, the module itself is condemned.
   Typical fix: Replace the PCM. The new module must be programmed to the vehicle's specific VIN and configuration.
   Est. part cost: $800-$1500
3. Low Battery Voltage or Poor Connections ⚪ Low Probability → Shop Vehicle Battery All modern control modules are sensitive to voltage. The Pacifica Hybrid's complex electrical system, with both a main 12V and an auxiliary battery, can be particularly susceptible to issues from a weak battery. Voltage drops or spikes ('brown-outs') can corrupt the data being written to the PCM's RAM, triggering a P0604 code.
   How to confirm: Test the 12-volt battery's health, state of charge, and ability to hold a load. Inspect all battery terminals, main engine grounds, and the PCM's own power and ground connections for corrosion or looseness. The Pacifica Hybrid has both a main and an auxiliary 12V battery under the hood; both should be tested. 🎬 Watch: How to replace the main and auxiliary batteries.
   Typical fix: Charge or replace the weak 12V battery (main or auxiliary). Clean or tighten all corroded or loose electrical connections.
   Est. part cost: $0-$250

Diagnosis Steps

1. Scan the vehicle for all diagnostic trouble codes. Note if P0604 appears with P062B or P060C.
2. Check for applicable Technical Service Bulletins. Specifically, reference TSB #18-044-26 for this vehicle.
3. If the TSB applies, the first step is to have a dealership update the PCM software. Crucially, the technician must connect a battery charger to ensure voltage does not drop below 13.2 volts or exceed 13.5 volts during the flash process, as instructed in multiple Chrysler TSBs.
4. If the code persists after the software update, perform a comprehensive test of the 12V main and auxiliary batteries' state of charge and health. Ensure they are providing stable voltage.
5. Thoroughly inspect the battery terminals, chassis grounds, and PCM connectors for any signs of corrosion, damage, or looseness.
6. If an aftermarket tuner or CAN bus-connected device (like a radio) is installed, remove it and return the vehicle to its stock configuration to see if the code clears.
7. If all wiring and voltage levels are correct and the software is up-to-date, the PCM is likely faulty.
8. Replace the PCM and program the new unit to the vehicle's VIN and specific options.

Parts You'll Likely Need

• Powertrain Control Module (PCM) (OEM #Varies by VIN. Part numbers are highly specific to year, model, and calibration and are often superseded. Must be ordered based on the vehicle's VIN.) — If a software update and electrical checks do not resolve the code, the internal hardware of the PCM has failed.
  Trusted brands: Mopar (OEM)
  OEM price range: $800-$1500
  Aftermarket price range: $500-$1000

Related Codes That Often Appear With This One

• P062B — This code for 'Internal Control Module Fuel Injector Control Performance' is listed in the same TSB (#18-044-26) and can be caused by the same software issue.
• P060C — This code for 'Internal Control Module Main Processor Performance' is also listed in TSB #18-044-26 and points to a related internal self-test failure that can be fixed with a software update.

Technical Service Bulletins (TSBs) & Recalls

• 18-044-26: Addresses P0604, P062B, and P060C, recommending a software update for the Powertrain Control Module.

Platform-Specific Known Issues

• A known software glitch can cause this code, which is correctable with a PCM reflash as per TSB #18-044-26.
• This model has been subject to several high-profile recalls related to the hybrid propulsion system that cause stalling or loss of power, including recall 03A (NHTSA 23V-010) for an internal transmission wiring connector and recall 03B (NHTSA 23V-844) for a Power Inverter Module (PIM) software flaw. While these do not directly cause P0604, they highlight the extreme sensitivity of the vehicle's control modules to software and communication errors, reinforcing why a software update should always be the first step for a P0604 code.

Mechanic-Grade Diagnostic Values

• PCM Power Supply Voltage (Cranking) — expected: Should stay above 9.0 V. Failure: A voltage drop below 9.0 V during cranking indicates a weak battery or poor connection, which can corrupt RAM.
• PCM Ground Circuit Resistance — expected: Below 0.1 Ω. Failure: Resistance higher than 0.1 Ω indicates a poor ground connection, which can cause floating voltages and logic errors.
• PCM Flashing Voltage — expected: Maintain between 13.2 V and 13.5 V. Failure: Voltage dropping below 13.2 V or climbing above 13.5 V during a software reflash can interrupt the process and permanently damage the PCM.

Scan Tool Commands That Help

• wiTECH 2.0: Restore Vehicle Configuration — After replacing and programming a new PCM, this function is used to ensure all vehicle options (like trim level, hybrid functions, etc.) 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.
🎬 See a walkthrough of the wiTECH 2.0 programming process.
• OEM-level Scan Tool: RAM-integrity test / Memory test — This is a specific self-test routine that can be initiated by the scan tool to directly check the PCM's RAM. A failure here confirms an internal hardware fault before condemning the module.

Wiring & Ground Locations

• Powertrain Control Module (PCM) — Located in the engine compartment, at the back of the engine bay on the driver's side, underneath the main air intake tube.. This is the module that is setting the code. Technicians need to access its connectors to perform power and ground tests directly at the module's pins to rule out wiring harness issues.
• Main Under-hood Fuse Box (Power Distribution Center) — Located in the engine compartment on the driver's side, it is a large black box with two release tabs.. This box contains the primary fuses and relays that supply power to the PCM. A faulty fuse or relay here would cut power to the module, causing various codes including P0604.
• Main 12V Battery — Located under the hood on the driver's side, behind a removable panel near the firewall.. This is the primary source of power for the PCM's Keep Alive Memory (KAM). A weak or failing main battery is a common cause of voltage-related module errors.
• Auxiliary 12V Battery — Located directly next to the main 12V battery under the hood, to the left when facing the engine. It is smaller, like a motorcycle battery.. This battery supports the vehicle's start-stop system and other electrical loads. A failure in the auxiliary battery can cause system-wide voltage instability, leading to codes like P0604.

Real Owner Repair Stories

• CarVents Forum User (Chrysler 300e Hybrid (similar platform)) — Power loss, engine control system warnings, and inconsistent performance, mimicking ECU failure.
  ❌ Tried (didn't work) Initial diagnosis pointed towards a faulty ECU.
  ✅ What actually fixed it A specialized diagnostic test revealed a failing main relay in the control system. The relay had visible burn marks on its contacts. Replacing the main relay and performing a system reset resolved all symptoms and avoided an unnecessary ECU replacement.