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My 2011 6.7 F250 with Lariat trim has been throwing the P0401 error code lately. It comes on AFTER a regen. It can be reset and then it comes back after the next regen.
Your EGR cooler is close to plugged or has plugged. Soot from daily driving empty, stop/go traffic, etc. (other than working it hard all the time) is the cause.
I was quoted $900 for repair when mine failed last year. It does power derate. Mine would struggle to pull a hill with the tractor behind me. Clearing the code would only buy me a few miles most of the time.
My guess is it isn't completely plugged vs mine would flag during normal driving. When an active regeneration is commanded, the actuator bypasses the EGR cooler to increase EGT to the DPF. Post AR, exhaust is then directed back through the EGR cooler. The ECM doesn't like the readings and flags the DTC.
The P0401 code comes and goes. After it comes in, I can immediately reset it. The activation of the code and resetting does not appear to be related to regeneration. I have seen the code come in any time (I have monitored it from 8 miles up to and past 350 miles) after the last reset. There is no pattern as to when it comes in. I have not noticed a change in the engine performance or mileage.
Is it harmful to continue to run the truck when it is acting like this?
Can a shop really troubleshoot and fix the issue with the code coming and going or should I wait until the code will not rest?
My truck threw this code when it had 44K miles. At that time, both the EGR valve and Cooler were replaced. My truck now has 82K miles on it. During the first time (at 44K) the dealer, first replaced the EGR valve. The code came back and they then replaced the cooler.
