2017-7-4 · Disassembly, Service, and Reassembly of a 1231 Oxygen Probe INTRODUCTION The 1231 heated oxygen probe is made up of 5 major parts: – 1. Alumina four-bore assembly and compression spring 2. Zirconia sensor, alumina tube, sensor gland and compression spring 3. Heater, inner sheath and gland assembly 4. Filter, outer sheath & nipple assembly 5.