Thimble type sensors feature a zirconium ceramic thimble that projects into the exhaust system and becomes electrically conductive at high temperature. The sensor element then sends voltage signals back to the engine management system to regulate the air to fuel ratio, for optimum efficiency. Bosch thimble sensors include a patented platinum power grid made with more platinum for optimized sensing, peak performance, and maximum service life. Zirconium and yttrium ceramic forms a tough base that resists cracking from mechanical and thermal shock. Particle filters protect against contamination for longer service life.