In this paper a fault tolerant state estimation (FTSE) framework is developed for reliable navigation. The framework features kinematic state estimation using Bayesian filtering of sensor measurements, and sensor fault detection and isolation. Another development is an uncoupled fusion architecture that allows the system state to be updated by asynchronous sensors, makes the system easily scalable and allows the system to degenerate gracefully during one or more sensor outage. A novel procedure to incorporate relative measurements, such as relative pose from stereo sensors, into the Bayesian filtering framework is also developed. In addition, a novel kinematic state transition model is developed that exploits the dynamics of UGV, provides a coupled linear and angular motion model and avoids over-fitting of measurement data. The FTSE system's performance is demonstrated based on results from processing real data.