Engine

P0604 — Control Module Random Access Memory (RAM) Error

Severity: medium Drive with care, to a shop

What P0604 means

During its self-tests the engine control module (ECM/PCM) detected a fault in its own random access memory (RAM), which holds temporary data and calculations. The memory is checked at every key-on and while running. When a read or write test fails, the module sets the code and turns on the check engine light.

Symptoms

  • Check engine light on
  • Intermittent no-start or hard starting
  • Engine stalls or runs roughly
  • Several systems stop working at once
  • Symptoms come and go depending on which internal function is affected
  • Code clears and returns

Possible causes

  1. Failing ECM/PCM
  2. Water damage or corrosion inside the module
  3. Voltage spike or low system voltage
  4. Weak or failing battery, poor terminal connections
  5. Open or corroded power or ground circuits to the module
  6. Outdated or corrupted software

How to diagnose

  1. Scan all modules and review freeze frame data and any other power or communication codes
  2. Test the battery: resting voltage, voltage under load and terminal condition
  3. Check charging voltage with the engine running
  4. Check module power and grounds: fuses, relays, connectors and wiring harness
  5. Inspect the module and connectors for moisture, corrosion or heat damage
  6. Check the software version and look for manufacturer bulletins or updates
  7. Clear the code and see whether it returns under the same conditions

Common fixes

  • Repair power and ground problems; clean or replace terminals and connectors
  • Replace the battery or repair the charging system
  • Update or reflash the ECM software
  • Dry and clean the module after water intrusion and fix the leak
  • Replace or repair the ECM, with programming and adaptation, if the code persists

Questions and answers

What does P0604 mean?

The control module found an error in its own internal RAM. It is most often the module itself, but unstable power or a weak battery can also trigger it.

Do I always need a new ECM for P0604?

No. Check the battery, charging, power, grounds and software updates first. Replace the module only if those are fine and the code keeps returning.

Can I drive with a P0604 code?

Only a short distance and with caution, such as to a shop. The engine could stall suddenly or refuse to start next time.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.