P0604: Internal Control Module Random Access Memory (RAM) Error

What it means

The control module detected an error involving its random access memory (RAM). The code alone does not establish whether the cause is internal hardware, software, or a power-supply issue.

At a glance

• Usually lights the check-engine light
• The engine or gearbox may go into limp mode

How it works

The module uses random access memory (RAM) for temporary data while it controls the engine and performs calculations. P0604 sets when its internal check detects a RAM error; a module fault, software issue, or supply voltage outside specification may be involved.

Common causes

Most likely first.

1. ECU internal RAM fault
2. Module software outdated, reflash may resolve
3. Supply voltage outside specification

Symptoms

• Check engine light on
• Possible limp mode or no-start
• Multiple follow-up faults across modules
• Reset/relearn may be needed after repair

How to diagnose it

1. Capture freeze-frame data and scan all modules for related faults before clearing codes, since multiple errors can indicate unstable shared voltage.
2. Check battery and charging-system condition and inspect module power and ground connections for looseness or corrosion.
3. Inspect the module connector and nearby harness for water intrusion, bent pins, or damaged wiring.
4. Check for module software updates or service information relevant to the RAM fault.
5. If power and software checks are satisfactory and P0604 returns, test the module circuits to the manufacturer's specification and assess for internal RAM failure.

Common fixes

• Repair poor battery, module power, or ground connections.
• Correct unstable battery or charging-system voltage.
• Reprogram the module if an applicable software update is available.
• Replace and configure the module if its RAM fault is confirmed.

Can I keep driving?

A steady warning light with normal engine behavior may allow a short trip, but avoid long journeys and heavy traffic because limp mode or stalling may occur. Stop driving if the engine becomes erratic, power drops, or it will not restart.