Possible causes

– Faulty Engine Control Module (ECM)
– Engine Control Module (ECM) Harness power supply circuit is open or shorted
– Engine Control Module (ECM) Programming

Tech notes

Check the ECM fuse, if fuse is OK try erasing the code first and if the code comes back you may have to reprogram or replaced the ECM.

When is the code detected?

Indicates the ECM has experienced an internal memory fault.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– Engine may not start

P0604 TOYOTA Description

The ECM continuously monitors its own internal memory status, internal circuits, and output signals transmitted to the throttle actuator. This self-check insures that the ECM is functioning properly. If any malfunction is detected, the ECM will set the code and illuminate the engine light.

TOYOTA Technical Service Bulletins for P0604 code