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P0604 OBD-II Trouble Code: Internal Control RAM Error

check engine light

P0604 trouble code definition

A P0604 trouble code is related to a vehicle’s engine control module (ECM) and or another control module and its random access memory (RAM). The code is an indication of an internal memory fault.

What the P0604 code means

P0604 is an OBD-II generic code for an internal memory failure between the ECM and the vehicle’s CAN, or controller area network. This is the connection between the ECM and other control modules such as the transmission control module. The ECM constantly monitors its own internal memory as well as circuits and output signals. If the self-check system detects an issue, it will ignite a P0604 code.

What causes the P0604 code?

A P0604 code can have numerous causes, but the most common are:

  • Faulty ECM/PCM fuse
  • Faulty battery terminal connection
  • Low battery voltage
  • Faulty ECM power supply circuit wiring
  • Faulty ECM

What are the symptoms of the P0604 code?

P0604 symptoms depend on whether or not other codes for other control modules are associated. If they are, problems will be dependent on what that module controls i.e. shifting issues with a TCM code. However, if a P0604 is all by itself, the vehicle may operate without any difference other than a Check Engine Light.

How does a mechanic diagnose the P0604 code?

A P0604 can be a cat and mouse game, or it can be as easily to remedy as clearing the code and resetting the ECM. Your mechanic will first check all codes and determine if there are other associated issues - addressing those first before taking on the P0604. If the code is all alone, the first move will be to clear the code, reset the ECM (typically by disconnecting the negative battery lead and waiting a few minutes) and go for a test drive. If the code does not return, a connectivity issue with the battery was probably the cause.

If the code returns, your mechanic will visually inspect all the wiring to and from the ECM, looking for damaged wires and bad grounds to be replaced and or cleaned, and check specific fuses for the ECM and PCM. Specialized OBD-II scanners can help determine the cause of issues instead of testing each CAN connection. If cleaning grounds and replacing wires do not work, replacing or rescanning the ECM may be necessary.

Common mistakes when diagnosing the P0604 code

If a P0604 is associated with another trouble code, it’s important to pay close attention to how these codes appear on a scanner as the order should indicate the route cause. For example, if a TCM code precedes a P0604, that transmission code should be dealt with first as it’s probably causing the P0604.

How serious is the P0604 code?

If a P0604 is by itself, it probably isn’t very serious and can be remedied by a cleaning, retightening or a clearing of the code. If it’s associated with another control module code, you could have a serious issue on your hands and should get it looked at as soon as possible.

What repairs can fix the P0604 code?

The most common repairs for a P0604 are as follows:

Additional comments for consideration regarding the P0604 code

P0604 codes are predominantly found in General Motors, BMW and Volkswagen models. It’s a smart move to clear the code and continue driving at the first instance of these codes as they can be random.

Need help with a P0604 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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