What does it mean?
I have found that when a code P0606 is stored, it means that the engine control module (ECM)/powertrain control module (PCM) has detected a processor malfunction.
Other control modules, including the transmission control module (TCM), body control module (BCM), antilock brake system (ABSCM) module, the traction control system (TCSCM) module, the instrument panel control module (IPCM), the anti theft module (ATM), and many others, may also detect a problem with the processor and cause a code P0606 to be stored. OBD II equipped vehicles typically refer to the primary powertrain controller as the PCM.
The primary focus of the PCM is to control operation of the engine and transmission but it also controls various functions of the other electronic systems listed above. That is not to say that these systems will not also have their own dedicated controller and it is very likely that they will. Information (data) is shared between these controllers using a large and complex web of wiring known as the controller area network (CAN).
When the ignition switch is turned on, before the engine is even started, the PCM begins a series of self tests to determine whether or not it is functioning properly. If the PCM detects a voltage supply malfunction, a system ground deficiency, or an internal processor error, a code P0606 will be stored and a malfunction indicator lamp (MIL) may be illuminated.
Depending upon the perceived severity of the malfunction, multiple ignition cycles (with a malfunction) may be necessary for MIL illumination.