Check engine light on and got codes P1234 , P1756 and P0402. Possible problem and solutions?

Question

Hello there. I would greatly appreciate it if you could help me with my van's problem. Engine Check light started flashing when car on yesterday and car engine started to sound like an ISUZU diesel engine (much rougher and making more noise). It seems that it looses power sometimes. Had it scanned and god OBDII codes P1234 CTP Learning-B2, P1756 L/Press Cont/FNCTN and P0402 EGRC-BPT Valve. Can you help decipher this? What could be the problem and possible solutions. Nissan Elgrand E50 3.8 Neo.