P249F. I had this one on mine. Was EGT12 that needed replacing. I first brought to the dealer, they couldn't pinpoint the problem, just reset the cel, charged me $100 diags, and sent me on my way. I ordered new sensor, swapped it out, and been fine ever since. I have 3 more to replace the others, but haven't gotten around to it yet.
From
my thread a year ago:
P249F - Excessive Time To Enter Closed Loop DPF Regeneration Control
Description: The powertrain control module (PCM) monitors the diesel particulate filter to determine that closed-loop control of a regeneration event occurs within a reasonable amount of time. This DTC sets if time in closed-loop operation is less than an expected threshold.
Possible Causes: Damaged
EGT12 sensor
Fuel injection concern
Damaged diesel oxidation catalyst
Biased diesel particulate filter pressure sensor
Damaged diesel particulate filter pressure sensor
Diagnostic Aids:
Application Key On Engine Off Key On Engine Running Continuous Memory
All GO to Pinpoint Test RC .