P0606: Control Module Processor
The engine control unit has detected an internal processor fault.
High risk
The engine may stall or go into limp mode. Have it checked soon.
Short answer · Can I keep driving with P0606?
With caution. The engine may run normally, stall or go into limp mode. Check battery and grounds first, then have the control unit checked.
What does P0606 mean?
Code P0606 means the engine control unit failed one of its internal self-tests. Before replacing it, check supply voltage, grounds and software updates.
Low supply voltage, poor grounds and water ingress can all trigger self-test failures. A replacement control unit usually needs programming to the car.
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 P0606
Can P0606 be caused by the battery?
Yes. A weak battery or poor grounds can make the self-test fail. Check them before replacing the control unit.
Will clearing the code help?
If it was a one-off event, perhaps. If it comes back, the unit or its supply needs diagnosis.
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.