Abstract: A coolant temperature of coolant in a circulation line system is measured through a coolant temperature sensor and is controlled by controlling a flow rate control valve. The flow rate control valve is diagnosed to determine whether abnormality of the flow rate control valve exists based on behavior of the measured coolant temperature, which is measured through the coolant temperature sensor during a warm-up period of an internal combustion engine.

Abstract: A target air-fuel ratio setting part has a sub-feedback part, a target air-fuel ratio enriching part, and a target air-fuel ratio changeover part. The sub-feedback part variably sets a target air-fuel ratio upstream of a catalyst on the basis of a detection signal of an O2 sensor provided downstream of the catalyst. The target air-fuel ratio changeover part uses, as the target air-fuel ratio, a rich target air-fuel ratio which is set by the target air-fuel ratio enriching part on conditions such that the target air-fuel ratio set by the sub-feedback part is rich. A cylinder-by-cylinder air-fuel ratio estimation part calculates a cylinder-by-cylinder air-fuel ratio on the basis of a detection value of an air-fuel ratio sensor and the target air-fuel ratio.

Abstract: ECU calculates variations of air-fuel ratios of respective cylinders and variations of air-fuel ratios of all the cylinders in variable intake valve lift devices of two cylinder groups. Presence and absence of an abnormality is determined on the basis of whether ratios of variations of air-fuel ratios of respective cylinders to variations of air-fuel ratios of all the cylinders are less than an abnormality threshold. Whether which of variable intake valve lift devices of the cylinder groups is abnormal is determined from control modes of the variable intake valve lift devices of the respective cylinder groups, and the relationship between that cylinder group, to which a cylinder being maximum in air-fuel ratio belongs, and cylinder group, to which a cylinder being minimum in air-fuel ratio belongs.

Abstract: An evaporated gas control system mounted on an automotive vehicle includes a canister for absorbing gas evaporated from a fuel tank and a purging passage for purging the evaporated gas into an engine. The purging passage is branched out to two passages, an upstream purging passage connected to an upstream portion of a throttle valve through an upstream valve and a downstream purging passage connected to a downstream portion of the throttle valve. Malfunction of the upstream purging passage including the upstream valve is detected based on changes in pressure of the air intake passage, which are responsive to opening and closing operations of the upstream valve. Preferably, the malfunction detecting process is performed by operating the upstream valve from a fully closed state to a fully open state under the condition where the throttle valve is fully closed.

Abstract: A fuel-vapor-processing system for an engine has a canister for accumulating fuel evaporation gas. The system has a leak-check apparatus for checking a leak on passages. The leak-check apparatus includes a leak-check means for carrying out leak-check processing when the engine if in a stopped state. The leak-check means operates only if a predetermined condition is satisfied. It is thus possible to reduce the number of times the leak-check processing is carried out and, hence, possible to reduce power consumption. For example, only if a relatively small leak is detected when the engine is in a running state, the leak-check processing is carried out in a stopped state to verify existence of such a leak. In the leak-check processing, the temperature of fuel, detected by a sensor or an estimated value, may be taken into consideration.

Abstract: A malfunction of a thermostat in a coolant circulating path is detected from an engine side coolant temperature in consideration of the following behavior of the coolant temperature. When an open-malfunction occurs, the coolant temperature becomes different considerably from that in the normal time in the temperature range in which the thermostat is to be normally closed. When a closure-malfunction occurs, the coolant temperature becomes different considerably from that during the normal time in the temperature range in which the thermostat is to be normally opened. Alternatively, the malfunction may be detected from a difference between the engine side coolant temperature and a radiator side coolant temperature.

Abstract: A malfunction of a thermostat in a coolant circulating path is detected from an engine side coolant temperature in consideration of the following behavior of the coolant temperature. When an open-malfunction occurs, the coolant temperature becomes different considerably from that in the normal time in the temperature range in which the thermostat is to be normally closed. When a closure-malfunction occurs, the coolant temperature becomes different considerably from that during the normal time in the temperature range in which the thermostat is to be normally opened. Alternatively, the malfunction may be detected from a difference between the engine side coolant temperature and a radiator side coolant temperature.

Abstract: An abnormality diagnosis apparatus is used for a secondary air supply system for an internal combustion engine. The system includes an air pump for supplying secondary air into an upstream of a catalyst in an exhaust gas passage of the internal combustion engine. A secondary air detecting means detects secondary air information. An abnormality diagnosis means performs an abnormality diagnosis of the secondary air supply system in accordance with the secondary air information detected using the secondary air detecting means. A temperature information determining means performs at least one of detection and estimation of air pump temperature information. A condition setting means performs at least one of setting and compensating a condition for evaluating normality and abnormality of the secondary air supply system in accordance with the air pump temperature information.

Abstract: A malfunction of a thermostat in a coolant circulating path is detected from an engine side coolant temperature in consideration of the following behavior of the coolant temperature. When an open-malfunction occurs, the coolant temperature becomes different considerably from that in the normal time in the temperature range in which the thermostat is to be normally closed. When a closure-malfunction occurs, the coolant temperature becomes different considerably from that during the normal time in the temperature range in which the thermostat is to be normally opened. Alternatively, the malfunction may be detected from a difference between the engine side coolant temperature and a radiator side coolant temperature.

Abstract: A secondary air control system supplies secondary air to the upstream of a catalyst purifying exhaust gas in an exhaust passage of an engine. A diagnostic device includes a secondary air detecting means that detects a secondary air information related to pressure of secondary air. An abnormality diagnostic means performs an abnormality diagnostic operation of the secondary air control system in accordance with the secondary air information. A voltage detecting means that detects a power source voltage information related to power source voltage supplied to the secondary air control system. An evaluating condition correcting means that corrects an evaluating condition, which is used for evaluating abnormality in the secondary air control system in accordance with a power source voltage information.

Abstract: A malfunction of a thermostat in a coolant circulating path is detected from an engine side coolant temperature in consideration of the following behavior of the coolant temperature. When an open-malfunction occurs, the coolant temperature becomes different considerably from that in the normal time in the temperature range in which the thermostat is to be normally closed. When a closure-malfunction occurs, the coolant temperature becomes different considerably from that during the normal time in the temperature range in which the thermostat is to be normally opened. Alternatively, the malfunction may be detected from a difference between the engine side coolant temperature and a radiator side coolant temperature.

Abstract: A misfire detector calculates the engine speed fluctuation quantity ??n for a predetermined period of time on the basis of the average engine speed on, which is the reciprocal of the time T120n that the crankshaft of the engine takes to turn 120 degrees. By comparing the calculated engine speed fluctuation quantity ??n with a misfire determination value REF, from which it can be determined whether the engine is misfiring, the misfire detector determines whether the engine is misfiring. The misfire detector detects the rotational fluctuation per combustion stroke of each engine cylinder and learns the variation of the detected rotational fluctuation values during normal combustion. From this learned value and the detected rotational fluctuation value per combustion stroke of the cylinder, the misfire detector determines whether the cylinder is misfiring or not.

Abstract: A malfunction of a thermostat in a coolant circulating path is detected from an engine side coolant temperature in consideration of the following behavior of the coolant temperature. When an open-malfunction occurs, the coolant temperature becomes different considerably from that in the normal time in the temperature range in which the thermostat is to be normally closed. When a closure-malfunction occurs, the coolant temperature becomes different considerably from that during the normal time in the temperature range in which the thermostat is to be normally opened. Alternatively, the malfunction may be detected from a difference between the engine side coolant temperature and a radiator side coolant temperature.

Abstract: ECU calculates variations of air-fuel ratios of respective cylinders and variations of air-fuel ratios of all the cylinders in variable intake valve lift devices of two cylinder groups. Presence and absence of an abnormality is determined on the basis of whether ratios of variations of air-fuel ratios of respective cylinders to variations of air-fuel ratios of all the cylinders are less than an abnormality threshold. Whether which of variable intake valve lift devices of the cylinder groups is abnormal is determined from control modes of the variable intake valve lift devices of the respective cylinder groups, and the relationship between that cylinder group, to which a cylinder being maximum in air-fuel ratio belongs, and cylinder group, to which a cylinder being minimum in air-fuel ratio belongs.

Abstract: An individual-cylinder air-fuel ratio estimation model is designed so as to consider the mixing of gases exhausted from adjacent combustion cylinders, and a movement by which a mixed gas arrives at the position of an air-fuel ratio sensor, in order that influences ascribable to the intervals (combustion intervals) of the adjacent combustion cylinders may be reflected on the estimation values of individual-cylinder air-fuel ratios. In evaluating the mixing of the gases which are exhausted from the adjacent combustion cylinders, there are considered the lengths and shapes of the exhaust manifolds of the respective combustion cylinders. In evaluating the movement by which the mixed gas arrives at the position of the air-fuel ratio sensor, there are considered a distance or volume from the confluence to the position of the air-fuel ratio sensor, and the exhaust gas quantities of the respective combustion cylinders.

Abstract: A vehicle ECU performs abnormality diagnoses including a deterioration diagnosis for a catalyst, a leakage diagnosis for an evaporative gas purge system, an abnormality diagnosis for an EGR system, and an abnormality diagnosis for a secondary air introducing system. During abnormality diagnoses, the ECU calculates the performance frequency for each diagnosis. When the performance frequency has reached the required level, the ECU performs the abnormality diagnosis under the normal abnormality diagnosing condition (performance condition, diagnosing method, and judging condition) in order to not adversely affect exhaust emissions, vehicle drivability, etc. If the performance frequency has not reached the required level, the ECU performs the abnormality diagnosis by changing the abnormality diagnosing condition to emphasize an increase of the performance frequency of the abnormality diagnosis, thereby increasing the performance frequency of the abnormality diagnosis.

Abstract: An emission control system has a catalyst and a sensor responding to a component of exhaust gas. In order to speed warming up the catalyst, the emission control system increases the amount of heat dissipated by exhaust gas. A diagnosis of the emission control system is carried out by determining whether the amount of heat dissipated by exhaust gas is sufficient or insufficient. The amount of heat dissipated by exhaust gas is represented by the length of time to an activated state of the sensor. In the diagnosis, the amount of heat generated by a heater provided in the sensor is taken into consideration.

Abstract: A leak check system executes a leak check processing. In the leak check processing, the system closes a canister valve and a purge valve to close the fuel vapor purge system. Then, the system detects and monitors a pressure in the fuel vapor purge system. During the leak check processing, the system detects a rapid change of the pressure that is caused by a deformation of a wall of a fuel tank. The system cancels or suspends the processing to avoid erroneous detection of the leak. If the leak check is canceled, the system opens the canister valve to open the fuel vapor purge system.

Abstract: A malfunction of a thermostat in a coolant circulating path is detected from an engine side coolant temperature in consideration of the following behavior of the coolant temperature. When an open-malfunction occurs, the coolant temperature becomes different considerably from that in the normal time in the temperature range in which the thermostat is to be normally closed. When a closure-malfunction occurs, the coolant temperature becomes different considerably from that during the normal time in the temperature range in which the thermostat is to be normally opened. Alternatively, the malfunction may be detected from a difference between the engine side coolant temperature and a radiator side coolant temperature.

Abstract: A malfunction of a thermostat in a coolant circulating path is detected from an engine side coolant temperature in consideration of the following behavior of the coolant temperature. When an open-malfunction occurs, the coolant temperature becomes different considerably from that in the normal time in the temperature range in which the thermostat is to be normally closed. When a closure-malfunction occurs, the coolant temperature becomes different considerably from that during the normal time in the temperature range in which the thermostat is to be normally opened. Alternatively, the malfunction may be detected from a difference between the engine side coolant temperature and a radiator side coolant temperature.