Engine derated no codes

Hi everyone needing some brain storming ideas please.

2006 kw w900l cat c15 accert

Check engine light came on with flash code 55...i know i know i know its a no code no issue code BUT this engine has derated and i cant get more than 35 boost out if it now at the most.

Usually if i get a 55 code the coolant might of dipped a bit low etc..ive checked all the usual suspects for that and it all looks good and i know wouldnt derate it anyway.

So just wondered if anyone else had run into this issue?
Going to try find a shop 2moro that can put the computer on it for any hidden codes.

Thanks

 

Update edit

The check engine light went out whilst i was driving and the boost returned to normal - 45 / 50.

Then i stopped and high idled due to temp for my 30 min break. As i took off the check engine light came back on and boost restricted again but only for about 3 mins then the light went off and boost returned again.

Stopped again for 15mins and as soon as i took off check engine light back on and boost restricted but this time it is didnt go out.

Should i be looking for a wire thats rubbing / is it just having a brain fart becoz ive had -22c / -7f or is there a looming engine or turbo issue??

Thanks

 

Ok thanks..was thinking we need to get it hooked up

 

Yea already done the rad. The fuel filter isnt a clear one...maybe chsnge thr filters coz it got so cold?
Will put the computer on it 1st tho.
Thanks