Replacing Miele freezer evaporation sensor

[Nickadye]

Hi, I have a Miele 6445 fridge/freezer that I bought second hand, but the freezer has always had an intermittent fault. Mile say I need to replace the 'electronic unit' (costing £210)! It has recently, for the first time, shown a fault code of F4 which from other posts I believe is 'freezer evaporation sensor faulty'. Is this just a wire, and if so which of the two in the freezer (one goes into the grill, the other onto a mounting plate at inside back of freezer draws)..... Or is it a whole electronic unit.

In either case, is this a simple fix for a DIYer, or is even removing and replacing a wire a difficult job. If difficult, there's no point in my throwing good money after bad.

Thanks in advance of advice!
Nick