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The "F5" error code on the element electronic control system (ESEC) means:"A harness, mother board or user interface board has failed" while the "F20" error code shown by the Electronic Oven Control means:"Communication failure between EOC and ESEC system.
The first thing I would do in such situation is check the harness and each connection. You can find the complete instructions in the
Service manual.
Here are the breakdown diagrams and
Replacement parts for FRG PLEFMZ99ECA | AppliancePartsPros.com
Gene.