The processor is becoming increasingly susceptible to transient faults with fluctuating voltage, widening operating temperature, and increasing clock frequency. Especially, processor, operating near threshold voltage for a low power, can expose to transient faults with the thin margin of process, voltage, and temperature. This paper presents a fault tolerant processor having on-chip fault monitor systems for processor core and cache, which detects faults and corrects faults, and a fault injector which injects faults for testing. The fault tolerant feature is analyzed by a fault injection and quantitative analysis complying with ISO26262 standard. As a result, the proposed work achieves 80 mu W/MHz energy efficiency, 850 MHz maximum frequency, 72% fault trap reduction, and 99.23% single point fault failure rate complying with ISO26262.