I have these but there may be more
P0115 03 Engine Coolant Temperature Circuit Low Input
P0115 07 Engine Coolant Temperature Circuit High Input
P0116 00 Minimum Coolant Temperature not Reached within Time Limit
looking at the list below and assuming the tech just reset your ecu faults to see what's going to pop up when you go back, (or was there other stuff done)
you may want to have someone check you havent black smoke coming out of the exhaust, when you apply a bit of throttle. this could be a knackerd injector - rather than producing a mist the fuel its more of a steady stream, thus using more fuel
Check air /fuel oil filters (this is why i suggested a full service as they will change the oil to)
Check the pipe from your air filter box to the egr isnt damage or loose and follow the pipe to the engine just to check as a hole or loose pipe could give incorrect reading on how much air is being given to the engine - so more fuel
it also may be sluggish / stutter /hesitant when you put your foot down.
Put some diesel injector cleaner in your tank and see if it improves your mpg.
I can send you a pic of the location of the egr value etc. if you need it or just google it
I'm no mechanic but had enough experience with diesels / poor mpg to look at the easy stuff first.
hope this helps
Common Causes Of Excessive Fuel Consumption, That May Or May Not, Turn On Your Check Engine Light: