Possible Cause
WARNING: This page is about a different car, the 2002 Nissan Pathfinder and 2002 Infiniti QX4. However, it is still accessible from the selected car via links, so may be relevant.
ECM illuminates MIL and sets DTC P1491 when an incorrect signal from TCM is sent to ECM. Possible causes are:
- Poor, loose or corroded terminal connections (communication line between TCM and ECM open or shorted).
- Dead or weak battery.
- Defective TCM.