Cel-Fi PRO Step-by-Step Troubleshooting Guide (SBS 9) September 20, 2021 21:28 Updated Which system icon is red? If one of the two system icons should be lit red, you should also see a matching error code. My Coverage Unit (CU) Icon is red and I am showing an Error 3. My Network Unit (NU) icon is red and I am showing an Error 4.