Monitoring device and method of a 3-way catalyst in the exhaust pipe of an internal combustion engine

Process for monitoring the function of a three-way catalyst in the exhaust gas channel of an IC engine comprises determining the lambda region; acquiring the size of the NOx signal and/or the value of a gradient of the NOx signal in a prescribed measuring interval within the lambda region; and comparing with threshold values and indicating damage to the catalyst on exceeding the threshold values. An Independent claim is also included for a device for monitoring the function of a three-way catalyst in the exhaust gas channel of an IC engine. Preferred Features: The lambda region comprises a stoichiometric operating point of the IC engine. During the function monitoring by a control device, a NOx signal of a NOx-sensitive measuring device and a lambda value are acquired using at least one lambda probe. A mixture composition to be burned in the direction of an actual operating point is influenced depending on the gradient of the lambda value and the NOx signal until a prescribed theoretical value for the gradient of the NOx signal is reached.