P0605: Internal Control Module Read Only Memory (ROM) Error
The engine control unit found an error in its own ROM memory.
High risk
The engine may run poorly or go into limp mode. Have it checked soon.
Short answer · Can I keep driving with P0605?
Only if the car runs normally, and then not far. The control unit may switch to limp mode or stop working. Have it checked soon.
What does P0605 mean?
Code P0605 means a self-test of the control unit found a fault in its read only memory (ROM). This memory holds the stored program of the control unit. A supply or ground problem, water damage or a failing control unit can cause it.
What the car does when the code is set
The check engine light comes on. Depending on the fault, the car may run normally, go into limp mode with limited power or stall. Other warning lights may appear because of the internal fault.
How the system works
The engine control unit runs continuous self-tests on its processor, memory and internal communication. Many units have a second, independent monitoring processor that checks the main one, especially for safety-relevant functions such as the electronic throttle. If these checks find a mismatch, a memory error or a reset, the unit stores a processor fault code and may switch to a limp-home mode with limited power to keep the car controllable.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Internal control unit faultThe processor or memory self-test fails.
- Supply or ground problemLow voltage or a poor ground can make the self-test fail.
- Water damageMoisture inside the unit.
- Software faultAn interrupted update or a known software issue.
How it is diagnosed
- Check supply and grounds firstMeasure voltage and grounds at the control unit as in the service data.
- Check for software updatesManufacturers sometimes release updates that fix this code.
- Inspect the unit and connectorLook for water ingress and corrosion.
- Repair or replace with codingA replacement control unit usually needs programming and immobiliser matching.
Questions about P0605
Does clearing the code help?
If the code returns after clearing and a test drive, the fault is real. A workshop then checks the supply and ground first, and may reprogram or replace the control unit.
Can a jump start damage the control unit?
Voltage spikes from incorrect jump starting can damage electronics. Always follow the manual's procedure.
Is a used control unit an option?
Only if it can be programmed to your car, including immobiliser data. A specialist can advise.