Method for monitoring an exhaust gas sensor, in which it is determined whether at least one monitored event has occurred by evaluating heat quantities supplied by the exhaust gas sensor in a period of time and/or withdrawn from the exhaust gas sensor in the period of time, characterized in that the evaluation is carried out on the basis of an energy balance equation or on the basis of the energy conservation law or on the basis of the temporal derivative of an energy balance equation or on the basis of the temporal derivative of the energy conservation law, and in that the following heat quantities are determined and taken into account separately from one another during or before the evaluation: - heat dissipation between the exhaust gas sensor and its surroundings, - heat convection between the exhaust gas sensor and its surroundings, and - heat radiation between the exhaust gas sensor and its surroundings; and in that the sum of these heat quantities plus a change in the heat quantity stored by the exhaust gas sensor, which takes place during the period of time and is detected by a device for measuring temperature that is included in the exhaust gas sensor, is compared with a heating power of an electrical heating device of the exhaust gas sensor and it is determined from this whether the at least one monitored event has occurred, wherein the heat quantities are determined from other measured variables, including an exhaust gas temperature, at least in part taking a physical model of the exhaust gas sensor and its surroundings as a basis, wherein the occurrence of the monitored event is not taken into account in the physical model; wherein, if the monitored event corresponds to additional cooling of the exhaust gas sensor, as is the case, for example, when the exhaust gas sensor is flooded, the occurrence of the monitored event is inferred when the electrical heating power is greater than the sum of the heat quantities taken into account; and wherein, if the monitored event is associated with expected cooling of the exhaust gas sensor not occurring, as is the case, for example, when a gas inlet opening of the exhaust gas sensor is blocked, the occurrence of the monitored event is inferred when the electrical heating power is less than the sum of the heat quantities taken into account. - heat dissipation between the exhaust gas sensor and its surroundings, - heat convection between the exhaust gas sensor and its surroundings, and - heat radiation between the exhaust gas sensor and its surroundings; and in that the sum of these heat quantities plus a change in the heat quantity stored by the exhaust gas sensor, which takes place during the period of time and is detected by a device for measuring temperature that is included in the exhaust gas sensor, is compared with a heating power of an electrical heating device of the exhaust gas sensor and it is determined from this whether the at least one monitored event has occurred, wherein the heat quantities are determined from other measured variables, including an exhaust gas temperature, at least in part taking a physical model of the exhaust gas sensor and its surroundings as a basis, wherein the occurrence of the monitored event is not taken into account in the physical model; wherein, if the monitored event corresponds to additional cooling of the exhaust gas sensor, as is the case, for example, when the exhaust gas sensor is flooded, the occurrence of the monitored event is inferred when the electrical heating power is greater than the sum of the heat quantities taken into account; and wherein, if the monitored event is associated with expected cooling of the exhaust gas sensor not occurring, as is the case, for example, when a gas inlet opening of the exhaust gas sensor is blocked, the occurrence of the monitored event is inferred when the electrical heating power is less than the sum of the heat quantities taken into account. and in that the sum of these heat quantities plus a change in the heat quantity stored by the exhaust gas sensor, which takes place during the period of time and is detected by a device for measuring temperature that is included in the exhaust gas sensor, is compared with a heating power of an electrical heating device of the exhaust gas sensor and it is determined from this whether the at least one monitored event has occurred, wherein the heat quantities are determined from other measured variables, including an exhaust gas temperature, at least in part taking a physical model of the exhaust gas sensor and its surroundings as a basis, wherein the occurrence of the monitored event is not taken into account in the physical model; wherein, if the monitored event corresponds to additional cooling of the exhaust gas sensor, as is the case, for example, when the exhaust gas sensor is flooded, the occurrence of the monitored event is inferred when the electrical heating power is greater than the sum of the heat quantities taken into account; and wherein, if the monitored event is associated with expected cooling of the exhaust gas sensor not occurring, as is the case, for example, when a gas inlet opening of the exhaust gas sensor is blocked, the occurrence of the monitored event is inferred when the electrical heating power is less than the sum of the heat quantities taken into account.