i had two codes that were spotted. my engine light does not work for some strange reason, anyone know a possible solution?

P1768-Linear solenoid Problem- probable cause damage from worn clutch discs, the transmission needs to be rebuilt i was told. is this true... he was a mechanic but not a transmission specialist. He said he worked with this kinda stuff before..
P0171 Lean Exhast and
P0401 EGR system low flow
anyone know how to fix this or know what these mean