MAT - Manifold Air Temperature

A "Scan" tool displays temperature of the air entering the engine and should read close to ambient air temperature when engine is cold and rise as underhood temperature increases. If the engine has not been run for several hours (overnight), the Manifold Air Temperature (MAT) sensor temperature and coolant temperature should read close to each other. A failure in the MAT sensor circuit should set a Code 23 or 25. The code charts also contain a chart to check for sensor resistance values relative to temperature.