P0604 — Control module RAM error

P0604: Control module RAM error — what it means, the affected system and what to check before replacing parts.

Meaning, symptoms, causes and checks

The control-module self-test reports a problem with random-access working memory (RAM). This identifies a memory function rather than a particular external actuator or sensor. Power, software and internal diagnostics must be interpreted according to the controller documentation.

Affected system: Control module self-diagnostics

Symptoms

  • Difficult starting; unstable idle and limited power.

Possible causes

  • Faulty memory/software, unstable supply or water ingress.

What to check

  • Check battery, alternator, supplies and grounds; inspect module for moisture.

Also written as: P0604-00, P060400, PO604 (some scan tools add the fault-type byte, e.g. -00).