4.2TD code 21 F/Inj TmgF/B

[dannypatrol]

Hi everyone, I had my engine light popping up a week ago. My ECUtalk told me that the cause was code 21. I went to a mechanic and he checked it out. He told me he cleared the code and cleaned the sensors. Should be all good. 400km, same thing happens. But it isnt constant. Sometimes it popsup right away and other times the next day after clearing the code through my ECUtalk. Any recommendations on what I can do myself to fix it? What to look for etc. Google hasnt helped much and I am missing the related part from my service manual.

I am in Mulgrave (Vic) atm and will be travelling to Adelaide soon. Any recommendations on reliable and affordable mechanics is welcome to.