In this work is reported the development of ceramic sensors based on ZnO-doped ITO thin films for engine diagnostics able to withstand the harsh environments associated with exhausts. ZnO–ITO films were deposited by RF-sputtering and have been employed in the development of thin films-based carbon monoxide resistive sensors operating at high temperature (500 °C). ZnO–ITO films, with different Zn/In ratio and thickness around 3 µm., have been deposited by changing the power on the targets. The effects of both the working temperature and the ZnO loading on the sensors performances were investigated. Undoped ITO film has shown negligible response to CO, whereas ZnO–ITO films were found to be sensitive at the required working temperatures. The reported results show how the ZnO–ITO devices under study can be promising sensors for CO monitoring in real exhausts of car engines.