Patent ID: 8366906

Claim:
A method for monitoring residual oxygen in an exhaust gas using a lambda probe in which a measuring point for oxygen at a sensor is connected with a reaction chamber via a diffusion gap, which during operation of the probe drives a stream of oxygen I O2 along the diffusion gap by means of a controllably adjustable oxygen partial pressure p i , with a predetermined oxygen partial pressure p i being set in the reaction chamber as a desired value by an electrochemical oxygen ion pump driven by an electrical pump current I P , and thus the pump current, the strength of which is proportional to the strength of the oxygen stream driven along the diffusion gap, can be used as a measurement parameter for the partial pressure p m of the residual oxygen in the exhaust gas, comprising: monitoring the residual oxygen during a normal operating phase (N) to obtain a normal operating phase pump current, operating the lambda probe intermittently for test purposes in two phases (H, L) in which operating phases the oxygen partial pressure p i in the reaction chamber adopts a minimum value and a maximum value respectively, thereby obtaining a high and a low operating phase pump current, respectively, and changing between the named operating phases, by registering the respective pump currents I p , comparing the pump currents I p with empirical values, and deriving conclusions with regard to the ability of the probe to function from this comparison so that in the case of a lacking or faulty ability to function, measures can be introduced to exchange the sensor.