Well, my check engine light turned on today and those were the two codes I pulled.

P1128 - CLOSED LOOP FUELING NOT ACHIEVED - BANK 1
P1129 - CLOSED LOOP FUELING NOT ACHIEVED - BANK 2


When Monitored:
Engine running in closed loop mode.

Set Condition:
Enable conditions are met and the 02 sensor has not been in closed loop control at least once on each of the two consecutive trips, the MIL illuminates and the DTC is set. Two Trip Fault. Three good trips to turn off the MIL


Possible Causes

RESTRICTED FUEL SUPPLY LINE
FUEL PUMP INLET STRAINER PLUGGED
FUEL PUMP MODULE
O2 SIGNAL CIRCUIT
O2 RETURN CIRCUIT
O2 SENSOR HEATER OPERATION
O2 SENSOR
MAP SENSOR OPERATION
ECT SENSOR OPERATION
ENGINE MECHANICAL PROBLEM
FUEL FILTER/PRESSURE REGULATOR (HIGH)
PCM
This is a common occurrence on forums for guys who want to replace their 02 sensors just for the hell of it as part of preventative maintenance... and usually use generic or lower quality Bosch sensors which tend to be too slow transitioning for Chrysler vehicles.

Me? Well, I didn't change a thing and my Xk has 33k miles on it (thought it is an 07) so I doubt that both upstream sensors decided to fail at the same exact time.

If it comes back on i'll do some trouble shooting (check out fuel pressure, coolant temp and MAP readings) and go from there.