Abstract: A method of monitoring functional capability of a soot sensor that is responsive to deposition of soot from an exhaust gas stream on a sensor surface comprises acquiring a measurement signal of the soot sensor and running a plausibility check, in which it is ascertained whether the measurement signal agrees with an expected finding. According to the invention it is detected whether conditions are present, on which liquid, e.g. water, from the exhaust gas stream condensates on the sensor surface. Additionally or alternatively, such conditions are produced. The plausibility check then includes ascertaining whether the measurement signal reflects the condensation of liquid. The detection of presence of conditions for condensation comprises a measurement or an estimation of temperature on the sensor surface.