P0604 code meaning
Internal Control Module Random Access Memory (RAM) Error
Powertrain system Generic code P06xx codes Check engine light
What P0604 means
P0604 means the module's working memory (RAM) failed its self-test: a value written to a cell does not read back correctly, a built-in hardware test fails, error correction reports faults, or protected memory is written without permission. GM's engine module scans the whole RAM within 30 s of start-up and then keeps checking in the background, setting the code after repeated failures with the lamp in the first trip; Ford tests RAM during initialisation, the GM gateway with error correction at start (two trips). Unlike most memory codes, P0604 is used the same way by GM, Ford, Chrysler and Saab. Consequences depend on the module: a transmission module goes into limp mode with maximum line pressure and a fixed gear, an engine module may reduce power. The code alone does not say which module set it – the scan tool shows whether it is the engine, transmission, brake or body module.
P0604 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0604
- Check engine light on
- Limp mode or transmission limp mode
- Intermittent stalling or starting problems
- Several module codes at the same time
Common causes of P0604
- Most likelyInternal hardware defect of the module (RAM)
- PossibleLow voltage, voltage dips or a poor ground or supply at the module
- Less likelyFaulty module software (update available)
- Less likelyMoisture or corrosion in the module or at its connector
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Engine control moduleControl module power supplyControl module ground
What each part of P0604 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 6 | Area: computer (engine control module) and output circuits. |
| 04 | The exact fault in that area. |
What to do next
- Note P0604 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0604
What does P0604 mean?
P0604 means "Internal Control Module Random Access Memory (RAM) Error". P0604 means the module's working memory (RAM) failed its self-test: a value written to a cell does not read back correctly, a built-in hardware test fails, error correction reports faults, or protected memory is written without permission. It is a generic code, so it means the same on every make.
Is it safe to drive with P0604?
Drive gently and only to a workshop. With P0604 the car can go into limp mode (reduced power) to protect itself.
Will P0604 fail an emissions test?
Yes, it can. P0604 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0604 to fix?
Difficulty: hard. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P0604 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.