DTC P0606: ECM / PCM Processor: Description

The ECM continuously monitors its internal processors (CPUs). This self-check ensures that the ECM is functioning properly. This is diagnosed by internal "mirroring" of the main and sub CPUs to detect processor errors. If outputs from the processors deviate from the standard, the ECM will illuminate the MIL and set a DTC immediately.

HINT: 

The MIL does not illuminate when a malfunction is detected in the CPU peripheral circuit of the ECM. It illuminate when a malfunction is detected in the ECM internal circuit: accelerator pedal position, brake switch, cruise control and throttle position.