Abstract: Resolver systems are described that generate an estimate &phgr; of a rotatable member's position angle &thgr; and provide fault signals which monitor the reliability and accuracy of the estimate. The fault signals are formed from a monitor signal which multiplies resolver and estimate signals to derive information on the absolute and relative levels of resolver sense signals. At least one fault signal is formed from a loop error signal of the system servo loop. The fault signals report on, for example, mismatched sense signals, out-of-range sense signals and loss of position tracking to thereby enhance accuracy and safety in various resolver applications.