L257 = Solenoid current too low AUX 2
L276 = Voltage at solenoid AUX 2+ permanently low
(there is an AUX 2- also but the rest of the book refers to the solenoids as A or B with no distinction to if A or B is + or -)

B- comes from pin 113 on the main control
goes through 2x5:7 & 8 back to pin 44 for solenoid 2Y7 (aux 2 dir B)
also B- splits to go through solenoid 2Y8 (aux 2 dir A) and back to pin 45 (common B- from pin 113 but ONLY for aux 2 A & B, all functions have their own B- from individual pins on the control)

2Y7 and 2Y8 are the 2 opposing solenoids on the opposite end of the valve from the return hose (furthest from port T)
make sure you dont have any cable breaks/ corrosion
disconnect the battery negative
unplug the connectors at the computer and solenoids
make sure you have continuity from pin 113 to the solenoids common B-
check from the solenoids negative back to their respective pins as mentioned above

i dont have any info on what the coils should read, cant find anything on that in the manual (maybe some1 else can jump in on that)
if all checks good
it could be the computer itself thats bad
i have a feeling its a bad wire or connection seeing its intermittent


i modified this post as i read the schematic closer
at first i thought it had common B+ from pin 113
but it looks like each coil (44 for 2Y7 & 45 for 2Y8) gets a variable signal then out to a common negative (pin 113 - marked 0V on the schematic)
so if something reads funny here thats why
it would help if my schematic was in English not German lol

good luck!
email is in my profile if you need anything

if you're the operator and none of this makes sense call a Linde dealer lol