In this article, a new investigation on a low temperature electrochemical hydrocarbon and NO_x sensor is presented. Based on the mixed potential based sensing scheme, the sensor is constructed using platinum and metal oxide electrodes, along with Yttria-Stabilized Zirconia (YSZ)/Strontium Titanate (SrTiO₃) thin film electrolyte. Unlike traditional mixed potential sensors which operate at higher temperatures (> 400⁰ C), this potentiometric sensor operates at 200⁰ C with selective hydrocarbon (HC) and NO_x response in the open-circuit and biased mode respectively. The possible low temperature operation of the sensor is speculated primarily due to the enhanced oxygen ion conductivity of the electrolyte, which may be attributed to the space charge effect, epitaxial strain, and atomic reconstruction at the interface of YSZ/STO thin film. The response and recovery time for the NO_x sensor are found to be 7 seconds and 8 seconds respectively. The sensor exhibited stable response even after 60 days of testing, with 9.4% decrease in HC response and a 1.9% decrease in NO_x response.