Possible causes

– Engine Control Module (ECM) may be faulty
– ECM harness power supply circuit is open or shorted
– ECM harness ground circuit is open or shorted

Tech notes

Try erasing the code first, if the light comes back ON you may have to replaced the ECM to repair the problem.

There is a factory service bulletin for the following Nissan models:

2002 Nissan Altima
2003 Nissan Altima
2004 Nissan Altima
2005 Nissan Altima
2002-2005 Nissan Altima Service Bulletin OBDII Code P0605

Symptoms

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

P0605 NISSAN Description

The Engine Control Module (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 sets the P0605 code and illuminates the MIL.

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NISSAN Technical Service Bulletins for P0605 code