P0604: Internal Control Module Random Access Memory (RAM) Error
What to do
May run in a reduced-power mode. This is an internal module fault, so expect a specialist rather than a parts replacement — but ask for the battery, charging system and module earths to be checked first, because a poor supply makes a healthy module report internal faults.
What this code means
The module's working memory has failed a self-test. RAM is where calculations happen moment to moment, so a fault here is more serious than one in stored settings — the module cannot rely on its own arithmetic.
Modules generally respond by falling back to a default strategy, which is why the usual presentation is limp mode rather than a dead vehicle. Genuine RAM failure is uncommon and is a hardware fault, but heat and vibration are the usual accelerators, and a module mounted in the engine bay lives with both.
Before accepting that a module has failed internally, rule out the supply. Marginal voltage and a poor earth both cause modules to fail self-tests while the hardware is sound.
Likely causes
Start here
- Failed control module · specialist
- Low system voltage disrupting communication · moderate
- Corroded earth connection · moderate
Less common
- Water ingress into module · specialist
- Degraded module memory · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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