Microfluidic biochips are widely accepted as the medical technology of the future. The reflection of this fact can be seen on the growth rate of the biochip industry as well. As these chips are used for many safety-critical applications, the testing and diagnosis of faults on them is of prime importance. In this paper, we present a simple approach for diagnosing faults on flow-based biochips using a two-stage search space pruning technique. The proposed technique employs a graph-theoretic bi-connected component based analysis which is much simpler and faster than those previously reported in the literature. © 2017 IEEE.