Method for Diagnosing an Exhaust Gas Catalytic Converter and/or an Exhaust Gas Sensor of a Motor Vehicle Internal Combustion Engine

Abstract

A method for diagnosing an exhaust gas catalytic convertor and/or an exhaust gas sensor arranged downstream and/or upstream of the exhaust gas catalytic convertor in an exhaust gas system of a motor vehicle internal combustion engine. The internal combustion engine is operated with an air/fuel mixture having a substoichiometric air/fuel ratio. The internal combustion engine is switched off and an unfired towed operation with disabled fuel supply is performed in which air drawn in by the internal combustion engine is conveyed through the exhaust gas system to the exhaust gas catalytic convertor and exhaust gas sensor. The internal combustion engine is then operated with a substoichiometric air/fuel ratio and a signal of the exhaust gas sensor is evaluated with regard to a predefinable evaluation criterion, the signal being provided at least in a period of time between switch-off and the subsequent self-running of the internal combustion engine.

1 - 14 . (canceled) 
     
     
         15 . A method for diagnosing an exhaust gas catalytic convertor or an exhaust gas sensor, which is arranged downstream or upstream of the exhaust gas catalytic convertor, in an exhaust gas system of a motor vehicle internal combustion engine, the method comprising:
 a. operating the internal combustion engine with an air/fuel mixture having a substoichiometric air/fuel ratio;   b. switching the internal combustion engine off;   c. once the internal combustion engine has been stopped, carrying out unfired towed operation with a disabled fuel supply, wherein air drawn in by the internal combustion engine is conveyed through the exhaust gas system to the exhaust gas catalytic convertor and the exhaust gas sensor;   d. starting self-running of the internal combustion engine with fired operation and a substoichiometric air/fuel ratio; and   e. evaluating a signal of the exhaust gas sensor with regard to a predefinable evaluation criterion, wherein the signal is provided at least in a period of time between switch-off and the subsequent self-running of the internal combustion engine.   
     
     
         16 . The method according to  claim 15 , wherein the method is carried out in a motor vehicle having an electric motor drive. 
     
     
         17 . The method according to  claim 15 , wherein the exhaust gas sensor is a lambda probe with jump characteristic arranged downstream of the exhaust gas catalytic convertor in the exhaust gas system, and wherein the exhaust gas sensor is diagnosed. 
     
     
         18 . The method The method according to  claim 15 , wherein the exhaust gas sensor is a continuous lambda probe arranged upstream of the exhaust gas catalytic convertor in the exhaust gas system, and wherein the exhaust gas sensor is diagnosed. 
     
     
         19 . The method according to  claim 15 , wherein an exhaust gas catalytic convertor is configured with oxygen storage capability and the exhaust gas catalytic converter is diagnosed. 
     
     
         20 . The method according to  claim 15 , wherein the internal combustion engine is operated with an air/fuel mixture having a lambda value of approximately 0.98 in method step a. 
     
     
         21 . The method according to  claim 15 , wherein the internal combustion engine is supplied with an air/fuel mixture having a lambda value in a range from approximately 0.98 to approximately 0.90 in method step d. 
     
     
         22 . The method according to  claim 15 , wherein the signal of the exhaust gas sensor is evaluated with regard to at least one of the following evaluation criteria: signal gradient, dead time, settling time and symmetry.