This paper aims at detecting soft faults, i.e. degradations, in Y-shaped communication networks and locating the faulty branch. The proposed method is based on the transmission coefficient (TC) between each source and the receivers. The estimation of the TC is performed online by power line communication technology through orthogonal frequency division multiplexing scheme. Then, a health indicator per receiver is computed and sent back to the source, which computes a set of structured residual signals for fault detection and localization. This method is validated by data collected on a laboratory test bench. To enhance the robustness of the residuals to noise, modified residuals are proposed. These new residuals are obtained by weighting the centered residuals by the Frequency Response Assurance Criterion. The experimental results confirm the robustness of the weighted residuals while maintaining their sensitivity to soft faults.