A method of detecting misfire in a combustion engine of a motor vehicle engine includes measuring a speed of a crankshaft, calculating a modal coefficient for each cylinder of the combustion engine, and indicating a misfire for at least one of the cylinders based on the calculation of the modal coefficients.

A method of operating an oxygen sensor system is provided where the system includes an oxygen sensor, the oxygen sensor including a pump cell, and wherein the oxygen sensor is connected to associated circuitry such that the associated circuitry controls operation of the pump cell. The pump cell includes a pump line connected to a pump electrode of the pump cell and a return line connected to a return electrode of the pump cell. The method includes, subsequent to a diagnostic process, raising the potential of the pump line for a predetermined period of time by injecting current onto the pump line.

Vehicle oxygen sensor heater diagnostic techniques comprise, upon detection of a set of cold start conditions of the vehicle, measuring an initial resistance of each of a set of two or more oxygen sensor heaters and determining whether any of the measured initial resistances is outside of a nominal resistance range. In response to an outlier oxygen sensor heater being outside of the nominal resistance range, each of the set oxygen sensor heaters is provided with an equal voltage for a period, the resistance of each of the set of oxygen sensor heaters is monitored during the period, and a malfunction of the outlier oxygen sensor heater is detected or matured when a difference between its resistance and the resistances of the other oxygen sensor heaters after the period is greater than a calibrated threshold.

In an engine system including an engine, and an exhaust gas recirculation device including a communicating pipe that communicates an exhaust pipe of the engine with an intake pipe, and a valve provided in the communicating pipe, and an electronic control unit, and its control method, the electronic control unit estimates the pressure in the intake pipe as an estimated intake pressure, and performs a jamming diagnosis to determine whether foreign matter is stuck in the valve, by comparing an intake pressure difference between a detected intake pressure and the estimated intake pressure with a threshold value, when a diagnosis condition including an opening change condition that the target opening becomes equal to or larger than a first predetermined opening and then becomes equal to or smaller than a second predetermined opening that is smaller than the first predetermined opening is satisfied.

Methods and systems are disclosed for operating an engine that includes a knock control system. The method and system may increase opportunities to learn one or more engine knock background noise levels via changing poppet valve timing and/or fuel injection timing. The method and system may also improve knock detection if knock sensor degradation is suspected.

A method for operating an exhaust gas recirculation system using rationality diagnostics for an automobile vehicle includes: estimating an oxygen storage content (OSC) of a catalytic converter of a vehicle; comparing an amount of oxygen stored in the catalytic converter to an OSC threshold; initiating a closed oxygen storage control (COSC) event for a predetermined one of multiple cylinders of an engine of a vehicle if the OSC threshold is met or exceeded, the COSC event targeting a rich air-fuel equivalence ratio (EQR) for the predetermined one of the multiple cylinders; and directing a fuel injector communicating with the predetermined one of the multiple cylinders to operate the predetermined one of the multiple cylinders at the rich EQR.

An abnormality diagnosis system of an air-fuel ratio sensor acquires a blowby gas flow ratio showing a ratio of the flow of blowby gas to the flow of gas to a combustion chamber and an output current of an air-fuel ratio sensor during fuel cut control in which an internal combustion engine stops the feed of fuel to the combustion chamber and at a plurality of points of time of different flows of blowby gas passing through a blowby gas passage and flowing to the downstream side of a throttle valve in the intake passage, calculate an output current of the air-fuel ratio sensor corresponding to a blowby gas flow ratio smaller than the blowby gas flow ratios acquired at the plurality of points of time, based on the acquired blowby gas flow ratio and output current, and judge the air-fuel ratio sensor for abnormality based on the calculated output current.

A method for identifying faulty components of a fuel injection system is disclosed, wherein a secondary injection is performed individually by each injector during a test routine, after the secondary injection several predefined parameters of the fuel injection system are determined, and a combined assessment of the determined parameters is used to draw conclusions about whether or not components of the fuel injection system are faulty.

A method provides a diagnostic on a combined humidity and temperature sensing device including a humidity sensor having a humidity sensing element, a temperature sensor, and a heater. The method comprises obtaining a first temperature and a first relative humidity, heating the humidity sensing element with the heater, obtaining a second temperature and a second relative humidity after heating the humidity sensing element, and determining a difference between the first temperature and the second temperature and a difference between the first relative humidity and the second relative humidity. Diagnostic information representative of a possible malfunction of the humidity sensor is output when the difference between the first temperature and the second temperature is higher than a predetermined temperature difference threshold and the difference between the first relative humidity and the second relative humidity is lower than a predetermined humidity difference threshold.

A method of predicting the temperature of a resistive heating element in a heating system is provided. The method includes obtaining resistance characteristics of resistive heating elements and compensating for variations in the resistance characteristics over a temperature regime. The resistance characteristics of the resistive heating element include, but are not limited to, inaccuracies in resistance measurements due to strain-induced resistance variations, variations in resistance due to the rate of cooling, shifts in power output due to exposure to temperature, resistance to temperature relationships, non-monotonic resistance to temperature relationships, system measurement errors, and combinations of resistance characteristics. The method includes interpreting and calibrating resistance characteristics based on a priori measurements and in situ measurements.