DTC P1605: A/T Diagnosis Communication Line (3.3L): Description
WARNING: This page is about a different car, the 2002 Nissan Xterra and 2002 Nissan Frontier. However, it is still accessible from the selected car via links, so may be relevant.
The malfunction information related to A/T is transferred through the circuit from Transmission Control Module (TCM) to ECM.