Future long duration manned space missions require a reliable sensor to monitor cabin oxygen (O2) pressure. This paper presents a concept for a solid zirconia O2 sensor capable of automatic self-test and calibration without the need for consumable materials. The operation and the techniques used to verify proper performance and to calibrate the sensor are described.The sensor design incorporates both potentiometric and coulometric measuring techniques operating simultaneously and independently of each other. Coulometric measurements are used to calculate the cabin sample O2 pressure without comparison to any reference state; potentiometric measurements are simple and reliable. The use of independent measurements permits the verification of results obtained with either technique and thus greatly enhances confidence. The design includes fault diagnostics which takes corrective action if a fault occurs. A breadboard sensor has been constructed and is being operated continuously in the laboratory. Preliminary test results are presented.