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Wanted to share my experience with P249C trouble code. I scoured the internet on this one trying to figure out what it meant. Though there was lots of information regarding the code and it being related to the after treatment system, I could not seem to find anything specifically pointing to the problem on the ecodiesel.

For reference I have a 2018. This code popped about a month ago. No loss of functionality to the truck. Not sure if that is normal or some byproduct of running the GDE compliant tune. I was concerned the truck would derate due to this codes being some how tied into emissions. Never did.

I ended up buying the OBD Link MX+ which I highly recommend. I checked whatever I could using the Alfa obd app (also great). Being that this code seemed to be something about the DEF not dosing (or so I thought) I tried running a dosing unit quantity test. i removed the dosing unit from the SCR and when running the test found there was no DEF being sprayed. I could hear the pump making some noises but no production. Seemed like a simple fix. To be sure I pulled off the DEF line at the tank/pump and removed the dosing unit from the other end and blew shop air through it. Ran the test again and same result.

I reluctantly went out and bought a new DEF pump which ran me somewhere around $800 (I do get a bit of a discount because of the industry I work in). I installed the pump which took me about 15 mins and ran the test again....no def. This time I looked through what other test were available through Alfa obd and found one called SCR emptying. What the hell lets try and see what happens. Sure enough DEF started spraying out. Okay problem solved? I wasn't sold but figured I would put it back together and see what happens. I believe the truck ran for about 2500km without a code. then suddenly it was back. P249C. This time it also has P242B - Exhaust gas temp sensor circuit performance - bank 1 sensor 3.

I opened up the OBD Link app on my phone (this one is the base app for OBD link tools) and saw something I didnt on the alfa app. I could read all 3 egt sensors. I believe obd link only shows 2 and does not list bank and sensor position. Once I could see this data it made WAY more sense. Both P249C and P242B popped at essentially the same time. I was seeing on the live data that EGT sensor bank 1 sensor 3 was reading very erratically (off by about 400f from the other sensors) and then defaulted to -40F.

I got a new sensor (about $45) and installed it. Code gone everyone happy now!

I hope this helps ANYONE struggling with this code in the future. Don't be dumb like me and throw a DEF pump at it. Your wallet will thank you.
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