P0604: Internal control module random access memory (RAM) error
The engine ECU has found a fault in its working memory (RAM). It can come from the power supply, but it is often the unit itself.
| Code | P0604 |
|---|---|
| System | Engine and transmission |
| Group | P06xx, Control unit and auxiliary outputs |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P0604 means
RAM is the memory the ECU uses for its calculations while the engine is running. This code means the ECU has tested that memory and found an error. Before writing the unit off, rule out battery, earth or supply problems.
Most common causes
- Low battery or unstable voltage
- Poor ECU earth or supply connection
- Moisture or corrosion in the ECU plug
- Interference from a faulty electrical component
- Internal ECU fault
Symptoms
- Engine warning light on
- Jerking, stalling or rough running
- Starting problems or limp mode
Can you drive with P0604?
With care The car may behave unpredictably or stall. Only drive when necessary and get it to a garage soon.
How to check it
Check the battery voltage on the scan tool and the condition of the earths before thinking about replacing the ECU. If the code comes straight back after clearing with correct voltage, an internal fault is most likely.
How to read and clear P0604 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0604 with this same explanation and whether it’s confirmed, pending or permanent.
With Free you read this code with its short description for nothing, and clear it if the engine stores it over standard OBD. With Pro you get the full explanation, how the car was running when it was logged (revs, temperature, load) and clearing in every control unit.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before the ITV. It’s all in how to read and clear fault codes and in the ITV and OBD.
Similar codes
- P0600 Serial communication link fault
- P0601 Internal control module memory checksum error
- P0602 Control module programming error
- P0603 Internal control module keep alive memory (KAM) error
- P0605 Internal control module read only memory (ROM) error
- P0606 ECM/PCM processor fault
- P0607 Control module performance
- P0615 Starter relay: circuit fault
- P0616 Starter relay: circuit low
- P0617 Starter relay: circuit high
- P0620 Generator control: circuit fault
- P0621 Generator lamp L control: circuit fault
P0604 is a generic code, so it means the same on any make, for example on BMW, Citroën, Ford, Mercedes-Benz, Renault, Volvo. See what Final OBD does on your car in makes and models.
What does code P0604 mean?
RAM is the memory the ECU uses for its calculations while the engine is running. This code means the ECU has tested that memory and found an error. Before writing the unit off, rule out battery, earth or supply problems.
Can you drive with P0604?
The car may behave unpredictably or stall. Only drive when necessary and get it to a garage soon.
How do you clear P0604?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0604 comes back.
Read it on your car
Final OBD reads the faults of every control unit for free, including each make’s own codes, and with Pro explains each one in plain English. Free clears engine faults at no cost.
Coming soon
Mid to late October 2026
If you want to try it in your car before anyone else, send us your email and we will add you as a tester.
info@finalobd.com