An extremely high output and durable thermoelectric sensor for detecting the quantitative content of combustibles in an exhaust gas. Thick film coatings of lithia-nickel and doped titanium dioxide provide two thermocouple junctions on a ceramic substrate. An exhaust gas oxidation catalyst adjacent one of the junctions provides a junction temperature differential when the ceramic body is exposed to exhaust gas flow. The output difference between the two junctions is proportional to the concentration of residual combustibles in the exhaust gas.