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Much like your home computer, your car’s powertrain control module (PCM) has two primary types of memory. The first is permanent, which is the read-only memory (ROM); the second one is temporary and is known as the random access memory (RAM).

If the PCM detects a problem with the RAM portion of its internal memory, it logs the P0604 code.

What Does the P0604 Code Mean?

Diagnostic trouble code (DTC) stands for “Internal Control Module Random Access Memory (RAM) Error.” It warns about an internal problem with the PCM’s random access memory (RAM) that stores its Keep Alive Memory (KAM) strategies.

car PCM
Code P0604 warns about an internal problem with the PCM’s random access memory (RAM) that stores its Keep Alive Memory (KAM) strategies.

The PCM relies on adaptive strategies when calculating important functions, such as fuel delivery and automatic transmission operation. It stores the most important data in dedicated KAM memory that keeps the calculations “alive” even after turning off the engine.

To ensure its ability to operate as designed, the PCM regularly runs internal self-tests on both the ROM and RAM portions of memory. If an issue is detected with the RAM function, code P0604 is set.

If you want to learn more about how issues related to the RAM can affect your vehicle, read our discussion about how the ECM/PCM’s RAM works.

Note: The Society of Automotive Engineers (SAE) set the generic code P0604. The vehicle’s manufacturer may have programmed a different definition for this code. Check the appropriate repair manual.

What are the Possible Causes of the P0604 Code?

Possible reasons for the PCM logging an internal control module RAM error code include:

  • A faulty PCM
  • PCM software in need of reprogramming

What are the Common Symptoms of the P0604 Code?

The KAM calculations govern various engine systems and processes. A problem with the RAM modules that store these settings can trigger these warning signs associated with an error code P0604:

The P0604 code can sometimes affect the vehicle’s performance, causing issues like the engine seemingly misfiring or even dying once the vehicle stops. In rare cases, you may not notice any symptoms at all.

car abs system
Your ABS Light could activate if your PCM is running code P0604.

How to Diagnose the P0604 Code

Fixing an internal control module RAM error code in your car’s PCM can challenge even the most skilled mechanic or technician. Unless you have absolute confidence in your DIY auto repair skills, it’s best to bring your vehicle to a shop.

For those who plan to diagnose the P0604 code in their vehicle, consult a repair manual and other appropriate sources of repair information.

How to Fix the P0604 Code

Like other trouble codes, the P0604 code has no universal resolution. The appropriate repair will vary depending on what triggered the code, and in some cases, your vehicle’s make and model.

Once you’ve determined what set the P0604 code, research ways to resolve it that are specific to your car. You can use auto repair resources and guides.

To get access to comprehensive factory repair information, consider securing an ALLDATA subscription. It’ll help you resolve not only the P0604 code but also any other issue that your car may experience in the future.

A Closer Look at the ECM/PCM’s Random Access Memory (RAM)

Computers, including the ECM/PCM, have two basic types of memory, namely read only memory (ROM) and random access memory (RAM). ROM is non-volatile, meaning, that it retains whatever is written there even if power is lost. RAM is like the workbench, where information is stored and retrieved. It can be written and erased on the fly. Nothing is erased from the ROM. Flashable ECM/PCMs have an EEPROM, which can be erased and rewritten when the computer is “flashed” with new programming.

When the computer powers down, the RAM is emptied, except in some cases, where adaptive learning information is stored, but that will be lost if Keep Alive power is disconnected. That’s why some vehicles won’t idle after the battery is replaced, because adaptive learning numbers that were slowly stored to maintain idle targets in spite of a dirty throttle body were lost and the “new vehicle” programming is all that’s available.

On a desktop PC, when you boot your computer up, the portion of the hard drive where the operating system is stored when the machine is shut down is the ROM. Booting the computer loads the operating system (Windows, etc.) into the RAM, which is like the computer’s electronic workbench. Other programs are also loaded in the RAM. All that information is dumped when you shut the computer down and restart it.

Vehicle PCMs are similar. If the RAM isn’t working, no adaptive learning functions are available. This can affect idle quality, fuel trim, transmission shift patterns, and many other things. Unfortunately, this typically indicates a fault with the ECM/PCM’s internal RAM.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic.

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