A method of diagnosing a temperature sensor provided at a rear stage of an air filter includes: comparing a heating condition factor with a factor threshold; when the heating condition factor is less than the factor threshold, calculating a deviation between a temperature of an intake manifold and a temperature of intake air at a rear stage of an air filter; comparing a temperature threshold with the deviation; and, when the deviation exceeds the temperature threshold, diagnosing the intake air temperature sensor provided at the rear stage of the air filter as failing. According to the method, failure of a temperature sensor provided at a rear state of an air filter of an engine room can be diagnosed.

A method for operating an exhaust gas purification system of an internal combustion engine, which can be operated in a lean operating mode and in a rich operating mode, is disclosed. The exhaust gas purification system has, arranged one after the other in the direction of flow of the exhaust gas, an ammonia-forming catalyst, a first exhaust gas sensor, an ammonia-SCR catalyst, a nitrogen oxide storage catalyst and a second exhaust gas sensor. Exhaust gas sensors emit a first signal correlating with the nitrogen oxide content of the exhaust gas and a second signal correlating with the lambda value of the exhaust gas. In diagnostic operation, the ammonia storage capacity of the ammonia-SCR catalyst and the oxygen and optionally the nitrogen oxide storage capacity of the nitrogen oxide storage catalyst can be determined by analyzing the signals of the first and second exhaust gas sensors.

A method of regenerating a lean NOx trap (LNT) of an exhaust purification system provided with the LNT and a selective catalytic reduction (SCR) catalyst may include: determining whether a regeneration release condition of the LNT is satisfied; determining whether a regeneration demand condition of the LNT is satisfied; and performing regeneration of the LNT if the regeneration release condition of the LNT and the regeneration demand condition of the LNT are satisfied. In particular, the regeneration release condition of the LNT is satisfied if all of an engine operating condition, an LNT state condition, and a lambda sensor synchronization condition are satisfied.

A diagnostic system and method that (a) that uses models indicative of both successful firing and skips to determine if cylinders of a skip fire controlled internal combustion engine have successfully fired or successfully skipped and (b) uses filtered exhaust gas pressure readings for detecting faults associated with EGR systems and/or turbocharger systems.

The exhaust purification device of an internal combustion engine comprises a catalyst 20 arranged in an exhaust passage and able to store oxygen; and an air-fuel ratio control device configured to control an air-fuel ratio of inflowing exhaust gas flowing into the catalyst. The air-fuel ratio control device is configured to perform a distribution forming control controlling the air-fuel ratio of the inflowing exhaust gas so that in the catalyst, a first region with an oxygen storage amount of equal to or greater than a predetermined value and a second region with an oxygen storage amount of less than the predetermined value are alternately formed along an axial direction of the catalyst. The total number of the first region and the second region formed by the distribution forming control is equal to or greater than three.

An apparatus includes circuitry configured to calculate a temperature of exhaust flowing into an exhaust after-treatment system as a first exhaust temperature, calculate a temperature of exhaust flowing out from the exhaust after-treatment system as a second exhaust temperature, calculate a rate of change over time of the first exhaust temperature and a rate of change over time of the second exhaust temperature, and judge if the exhaust after-treatment system is in a removed state removed from the exhaust passage based on a difference between the rate of change over time of the first exhaust temperature and the rate of change over time of the second exhaust temperature.

A method is proposed for regulating a fill level of an exhaust component storage of a catalyst (26) of an internal combustion engine (10), wherein the regulating of the fill level is done by using a system model (100), comprising a catalyst model (102), and wherein uncertainties of measured or model variables influencing the regulating of the fill level are corrected by an adaptation, which is based on signals of an exhaust gas probe (34) arranged at the outlet side of the catalyst (26). The method is characterized in that the adaptation takes multiple pathways (200, 210, 220), wherein signals from different signal regions (260, 280, 300) of the exhaust gas probe (34) situated at the outlet side are processed on different pathways. An independent claim is addressed to a controller designed to carry out the method.

Methods and systems are provided for a NO.sub.x sensor. In one example, a method includes heating a NO.sub.x sensor during a vehicle off in response to a cumulative heat energy applied to the NO.sub.x.

When an intake air amount is greater than or equal to the lower limit intake air amount and less than or equal to the upper limit intake air amount, a CPU sets, from the first cylinder group that increases a detection value of an upstream air-fuel ratio sensor, one of cylinders that has the smallest cutoff frequency, which is stored in a storage device, as a cylinder to which the supply of fuel will be cut off. Then, the CPU obtains the maximum value of an upstream air-fuel ratio as a maximum air-fuel ratio. When the maximum air-fuel ratio is greater than a determination value, the CPU determines that specific cylinder fuel cutoff control is normal. When the maximum air-fuel ratio is less than or equal to the determination value, the CPU determines that the specific cylinder fuel cutoff control is anomalous.

An engine device includes: an engine; and a control device that executes a return rich control that controls the engine so that an air-fuel ratio becomes rich over a predetermined period after the engine returns from the fuel cut. When the engine is intermittently stopped during the execution of the return rich control, the return rich control is executed for a period shorter than the predetermined period after the engine is restarted. Thus, when the engine is intermittently stopped during the execution of the return rich control and the engine is restarted thereafter, it is possible to suppress a total period of the return rich control from becoming long. As a result, it is possible to suppress an increase in the amount of hydrocarbons in the exhaust gas and suppress deterioration of emissions.