OBD codes / P0604
P0604
SeriousInternal Control Module RAM Error
Don't count on a car whose engine computer has failing working memory — stalling and no-starts can happen without warning. Keep driving minimal until it's diagnosed. Have the shop confirm clean power and grounds at the module before authorizing a replacement computer; a false failure from bad voltage is the outcome worth hoping for.
What this code means
P0604 means the engine computer failed a self-test of its RAM — the working memory it uses for live calculations while the engine runs. The module writes test data to memory, reads it back, and sets this code when the result doesn't match. A genuinely failed RAM chip can't be repaired separately, so a confirmed internal fault means reflashing rarely helps and module replacement is the realistic fix. That said, the same cheap culprits that plague all ECM internal codes apply here: low or unstable voltage, corroded connectors, and bad grounds can cause false failures, and a voltage spike can trigger a one-time error. Verify the power supply to the module and try a battery-disconnect reset before condemning the computer.
Symptoms you might notice
- Check-engine light, often persistent
- Stalling, misfiring, or erratic running
- Reduced-power / limp mode
- Intermittent or complete no-start
- Code returns immediately after clearing
What it costs to fix
Varies by vehicle — get it diagnosed.
The repair cost for this code depends too much on your exact vehicle and the underlying cause to quote a meaningful range. Confirm the cause first so you only pay for the fix you actually need.
Diagnose P0604 for my vehicle →Frequently asked
Can I drive with P0604?
It's risky. RAM is the computer's live working memory, and a fault there can cause stalling or a sudden no-start. Short essential trips at most, and get it diagnosed quickly.
Can P0604 be fixed without replacing the computer?
Only if the real cause is electrical — low voltage, a corroded connector, or a bad ground faking the failure. A truly failed RAM chip is inside the module, so a confirmed internal fault means replacement rather than repair.
Why doesn't a reflash fix a RAM error?
Reflashing rewrites the software, but RAM is physical working memory the processor uses while running. New software can't repair a bad memory chip, which is why persistent P0604 usually points to the hardware.
What should be checked before replacing the ECM?
Battery condition, charging voltage, the ECM's power feeds and fuses, its grounds, and the connector pins for corrosion. A module replacement also needs programming to your vehicle, so it's worth being certain first.
Seeing P0604 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0604 for my vehicleRelated trouble codes
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Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.