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 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: In a fuel vapor handling system of this invention, an ECU performs a leak check to check a leak of fuel vapor in a fuel vapor passage when the engine is at a stop. The ECU functions to detect the quantity of fuel during the engine stop. The ECU detects the quantity of fuel at the time of engine starting. Furthermore, the ECU compares the quantity of fuel measured at the time of engine starting with the quantity of fuel measured at the preceding engine stop, to thereby determine whether a filler cap was opened during the engine stop. When the filler cap was opened during the engine stop, a result of the leak check will be cancelled. When the filler cap was not opened, the result of the leak check will be determined.

Abstract: A fuel vapor control system has a controller that carries out a leak check processing after the engine is stopped. The controller includes a device that intermittently activates the controller itself or a part of the controller to sample an internal pressure of the fuel vapor passage. Then, after a predetermined time, the controller determines that whether the sampled values of the internal pressure indicate a leak or not by evaluating the sampled values. According to the arrangement, since at least a part of the controller is activated intermittently, the consumption of electricity can be reduced. The fuel vapor control system has a canister valve and a purge valve made of normally close type valves in order to reduce the consumption of electricity after the engine is stopped.

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 misfire detector calculates the engine speed fluctuation quantity &Dgr;&ohgr;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 &Dgr;&ohgr;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: An engine start is beforehand detected when a preparation operation to engine start is detected. When the preparation operation is detected based on a seat switch indicating that a driver seats himself on a driver seat, control of an electric current for a heater of an air/fuel ratio sensor is started. The air/fuel ratio sensor is then activated prior to the engine start. Failure diagnosis is conducted on a function for detecting the preparation operation. Namely, the seat switch is diagnosed as having failure, for instance, by the following. Even while a vehicle travels, the seat switch is in an OFF state indicating that no driver is seated. This structure can restrict the engine start without the air/fuel ratio sensor being pre-heated. It can also restrict deteriorating of emission.

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 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 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: Even after initiation of a fuel cutting operation, an estimated coolant temperature value is continuously renewed based on an engine operating state until a predetermined time period elapses. Thus, an increase in the coolant temperature during the fuel cutting operation can be estimated. Furthermore, overestimation of the increase in the coolant temperature during the fuel cutting operation can be avoided since the renewal of the estimated coolant temperature after the elapse of the predetermined time period is prohibited. In this way, possible deterioration of coolant temperature estimation accuracy caused by the fuel cutting operation can be minimized, allowing more accurate coolant temperature estimation. As a result, when abnormality of a thermostat is judged based on a difference between an actual coolant temperature and the estimated coolant temperature value, misjudgment of a normal thermostat as an abnormal thermostat can be prevented.

Abstract: In a diagnosis apparatus, when tank internal pressure does not decrease up to a given negative pressure at a time when a given time has lapsed after starting negative pressure introduction into an evaporation gas purge system line, it is determined that the purge system line is abnormal and the abnormal cause is determined based on the internal pressure change amount &Dgr;P. The diagnosis apparatus identifies a valve opening state locking of an atmosphere change over valve, if &Dgr;P>K2, a valve closing state locking of a purge control valve, if &Dgr;P≦K2, and a large amount of leakage, if K1<&Dgr;P≦K2. The internal pressure change amount &Dgr;P is detected during a normal driving operation, at which the purge control valve is intermittently driven to intermittently purge the evaporation gas in a state that the atmosphere change over valve is opened.

Abstract: A fuel evaporation control system is connected to an engine control system in which an air-fuel ratio in mixture gas supplied to an engine is controlled to an optimum level. Fuel evaporated from a fuel tank is absorbed by a canister, and the absorbed fuel is purged into the engine. Deterioration of the canister in its air-permeability is detected based on measured pressure in the fuel evaporation control system or calculated density in the purge gas, both the pressure and the density being measured or calculated under two different amounts of purge gas flow. Deterioration of the canister in its fuel-absorbing ability is also detected based on the purge gas density.

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 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: A fuel evaporation control system is connected to an engine control system in which an air-fuel ratio in mixture gas supplied to an engine is controlled to an optimum level. Fuel evaporated from a fuel tank is absorbed by a canister, and the absorbed fuel is purged into the engine. Deterioration of the canister in its air-permeability is detected based on measured pressure in the fuel evaporation control system or calculated density in the purge gas, both the pressure and the density being measured or calculated under two different amounts of purge gas flow. Deterioration of the canister in its fuel-absorbing ability is also detected based on the purge gas density.

Abstract: In a fuel vapor handling system of this invention, an ECU performs a leak check to check a leak of fuel vapor in a fuel vapor passage when the engine is at a stop. The ECU functions to detect the quantity of fuel during the engine stop. The ECU detects the quantity of fuel at the time of engine starting. Furthermore, the ECU compares the quantity of fuel measured at the time of engine starting with the quantity of fuel measured at the preceding engine stop, to thereby determine whether a filler cap was opened during the engine stop. When the filler cap was opened during the engine stop, a result of the leak check will be cancelled. When the filler cap was not opened, the result of the leak check will be determined.

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. The diagnosis can also be carried out before and after the warming up the catalyst. The heater can also be deactivated. Detection of an abnormality of a secondary air control system can be based on a component of exhaust gas. If the amount of heat dissipated by exhaust gas is found insufficient, additional control can be executed.

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 fuel vapor control system has a controller that carries out a leak check processing after the engine is stopped. The controller includes a device that intermittently activates the controller itself or a part of the controller to sample an internal pressure of the fuel vapor passage. Then, after a predetermined time, the controller determines that whether the sampled values of the internal pressure indicate a leak or not by evaluating the sampled values. According to the arrangement, since at least a part of the controller is activated intermittently, the consumption of electricity can be reduced. The fuel vapor control system has a canister valve and a purge valve made of normally close type valves in order to reduce the consumption of electricity after the engine is stopped.