Under the background of "carbon peak and neutrality" strategy, in order to solve the domestic urgent demand for the carbon footprint collection terminal and system, a solution based on electricity acquisition terminal and communication system is proposed, and a specific "virtual probe" testability design plan is also put forward by using hybrid boundary scan technology. By focusing on solving the problem of low accuracy in nonlinear "cluster" circuit fault diagnosis based on single type of fault feature, a fault diagnosis method is proposed that involves a fusion of wavelet packet transform and PCA feature layer, based on the study of wavelet packet transform, PCA and Volterra kernel feature extraction. Then, a decision-level fusion is conducted with the primary diagnosis results based on Volterra kernel feature. Experimental results have shown that the proposed method effectively improves the accuracy of fault diagnosis.