Fault light isn't in view. All the QRH says is that one or both loops are faulty. Logical that it is designed so that people don't decide to shut down a fully functional engine, due to a detector fault. The probability of both failing must be extremely slim anyway.
Edited to add, it is normally in the Normal Position and therefore requires both loops to fail for the fault light to illuminate. You can check if one has failed by selecting A or B.
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