I have a 2001 S type 4.0, just got it back last week from having a new engine due to a broken secondary timing chain ( thanks jagtechohio ) and a completely rebult transmission. We have driven the car nearly 200 miles with no troubles untill today, went to start it and it went into engine fail safe mode. I restarted the car and was ok except for the engine light is now on.
I pulled the codes and there are 2, p1589 & p1780. The 1780 shows to be a possible shifter problem? The 1589 shown to be unable to control throttle.
If anyone has any ideas or suggestions, please let me know. I want to be more informed on this before I contact the shop that rebuilt the transmission ( they also pulled the motor for me ). Thank you !

 

P1589 appears to mean that the PCM commanded the motor for the throttle to move to a position but it didn't go to the right position (or something along those lines). Firstly you may wish to see if it keeps occurring. And/or look for any issues around the throttle body (loose/chafed wires, water, staining, contamination etc). You could try cleaning it (you're not supposed to but as it's apparently already faulty what have you to lose?) with care and gently, using the cleaner for them or maybe carb cleaner. The throttle body is horribly expensive so IF it's deemed faulty you may want to try to get a used one.

It seems a bit odd to get P1780 as well. Two very different codes both very rare yet at the same time. Wiring problem? Battery? Water? Coolant leak? Be creative and attentive and really look closely in the engine bay.

If it MIGHT be the battery, it's (very!) cheap to replace compared to the other things it so far appears to be.