The performance of ad hoc routing protocols will significantly degrade, if there are malfunctioned nodes in the network. Fault tolerant routing protocols address this problem by exploring the network redundancy through multipath routing. Designing an effective and efficient fault tolerant routing protocol is inherently hard, because the problem is NP-complete and the precise path information is unavailable. This paper solves this problem by presenting an end-to-end estimation-based fault tolerant routing algorithm E/sup 2/FT. E/sup 2/FT deploys two complementary processes: route estimation and route selection. Through end-to-end performance measurement, the route estimation process gives improving estimation results via iterations. Based on these estimation results, the route selection process decides a multipath route for packet delivery. The route selection is refined progressively with the increasingly accurate estimation result using "confirmation" and "dropping" procedures. Through theoretical analysis and simulation, we show E/sup 2/FT can achieve a high packet delivery rate with acceptable overhead.