Abstract:
An electronic control unit improves a serviceability for a user of a vehicle by performing an abnormality diagnosis of the vehicle based on (i) storing a readiness information indicating that readiness is complete in a readiness storage, (ii) storing a history of normal diagnosis results from an abnormality diagnosis in a history storage, and (iii) relaxing a readiness complete condition for storing the readiness information in the readiness storage under control of a microcomputer, when the history stored in the history storage includes information of existence of the normal history. By using the relaxed condition for the abnormality diagnosis, readiness information is more quickly stored when performing the abnormality diagnosis. Also, diagnostic process is completed more quickly, facilitating the repair process and enabling the user to more quickly receive a desired service.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is based on and claims the benefit of priority of Japanese Patent Application No. 2015-005004, filed on Jan. 14, 2015, the disclosure of which is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure generally relates to an electronic control unit capable of performing an abnormality detection process for detecting an abnormality of a vehicle. 
       BACKGROUND INFORMATION 
       [0003]    Generally, a vehicle nowadays has many electronic control units (ECU)s installed in the vehicle, and among those ECUs, some have a self-diagnosis function for diagnosing an abnormality of the vehicle, which may be designated as On-Board Diagnostics (OBD). In recent years, OBD II standard is enacted, which is applicable to most of gasoline-engine vehicles and diesel-engine vehicles. According to the OBD II standard, the abnormality of the vehicle and the vehicle parts are diagnosable based on a regular monitoring of critical components and other conditions, such as an engine, an exhaust gas and the like. 
         [0004]    The ECU stores information indicative of abnormality of a vehicle to a memory unit when diagnosis items are diagnosed as abnormal, based on information of various sensors that are installed in a vehicle, which is then read out by an external device installed in a gas station or the like. The read-out information is utilized for an abnormality check or the like. See for example, a patent document, Japanese Patent Laid-Open No. 2004-151021 (patent document 1). 
         [0005]    When the self-diagnosis function is not properly functioning, the abnormality of sensors is not appropriately diagnosable. Therefore, the function of the abnormal sensor is configured to also be diagnosable as is (i.e., as the sensor is installed in the vehicle), and the diagnosis results are stored in the memory unit. 
         [0006]    For example, according to the OBD II standard, the abnormality diagnosis determination items and the abnormality diagnosis inspection items (i.e., designated as abnormality diagnosis items) are stored as readiness information in the memory unit when satisfied. In other words, when all items of the readiness information are satisfied, the vehicle is shippable from a factory, or is returnable to a user from a repair shop. 
         [0007]    The readiness information is erasable (i.e., can be “cleared”) by the external device according to the OBD II standard, which means the information is erasable from the memory unit. Here, the readiness information is considered as complete only after all abnormality diagnosis items are satisfied. The ease of satisfying an abnormality diagnosis item is different from item to item, and the time required for the determination of the diagnosis item also varies from item to item. In other words, a certain diagnosis item may take a very long time to be determined as satisfied when such an item is cleared. Therefore, especially when the vehicle has to be diagnosed in a short time in a shipping process from a factory or in a repair process before returning to a user from a vehicle dealer, such a long diagnosis time, for completing/satisfying all abnormality diagnosis items, is problematic. 
       SUMMARY 
       [0008]    It is an object of the present disclosure to provide an electronic control unit having an improved serviceability for a user of a vehicle. 
         [0009]    In one aspect of the present disclosure, an electronic control unit includes an abnormality determiner determining an abnormality of a vehicle by performing an abnormality diagnosis, a first storage, and storing a readiness information for use of the vehicle. The readiness information (i) indicates that the abnormality determiner has undergone all of a plurality of abnormality diagnosis items of the abnormality diagnosis and (ii) establishing that readiness is complete. The electronic control unit also includes a second storage (storing a history of the abnormality diagnosis, the history of the abnormality diagnosis including information of whether a normal history exists. The abnormality determiner applies a relaxed condition for the abnormality diagnosis, when the history of the abnormality diagnosis including the information of existence of the normal history is stored in the second storage at a time of determining the abnormality of the vehicle. The relaxed condition is more easily satisfied for completion of the readiness and the storing of the readiness information in the first storage, in comparison to a normal condition, when the history stored in the second storage is without the information of existence of the normal history. 
         [0010]    By using the relaxed condition for the abnormality diagnosis, the abnormality determiner is enabled to more quickly store the readiness information in the first storage when performing the abnormality diagnosis, in which a satisfaction of the condition of each of many items of the abnormality diagnosis may otherwise be difficult (i.e., may otherwise take a long diagnosis time). Therefore, the diagnosis process is quickly completed, facilitating the repair process and enabling the user to more quickly receive a desired service. 
         [0011]    In another aspect of the present disclosure, the abnormality determiner determines the abnormality of the vehicle without relaxing the condition for the abnormality diagnosis if the history stored in the second storage includes no normal diagnosis result, thereby performing the abnormality diagnosis according to a normal condition for the abnormality diagnosis. This enables the electronic control unit to find and determine an abnormality according to a normal flow of abnormality diagnosis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Objects, features, and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings, in which: 
           [0013]      FIG. 1  is a block diagram of an electrical configuration of an electronic control unit and a communication system in a first embodiment of the present disclosure; 
           [0014]      FIG. 2  is a flowchart of a first part of a diagnosis process in the first embodiment of the present disclosure; 
           [0015]      FIG. 3  is a flowchart of a second part of the diagnosis process in the first embodiment of the present disclosure; 
           [0016]      FIG. 4  is a flowchart of the diagnosis process in a second embodiment of the present disclosure; 
           [0017]      FIG. 5  is a flowchart of the diagnosis process in a third embodiment of the present disclosure; 
           [0018]      FIG. 6  is a flowchart of the diagnosis process in a fourth embodiment of the present disclosure; 
           [0019]      FIG. 7  is a flowchart of a first part of the diagnosis process in a fifth embodiment of the present disclosure; 
           [0020]      FIG. 8  is a flowchart of a second part of the diagnosis process in the fifth embodiment of the present disclosure; and 
           [0021]      FIG. 9  is a flowchart of the diagnosis process in a sixth embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Hereafter, embodiments of the present disclosure regarding the electronic control unit are described with reference to the drawings. In the following description, like numbers represent like parts or like functions, and the description of the like parts/functions is not repeated. 
       First Embodiment 
       [0023]      FIGS. 1-3  are diagrams concerning the first embodiment of the present disclosure. 
         [0024]    A communication system  1  shown in  FIG. 1  is provided with a plurality of Electronic Control Units (ECU)s  2 ,  3 , and  4  disposed in a vehicle, and ECUs  2  to  4  concerned are mutually-communicably connected via a communication line  5  of a vehicle network. Various kinds of sensors A 1 , A 2  (e.g. a temperature sensor A 1 ) and actuators B 1 , B 2 , etc., are connected to each of ECUs  3  and  4 , and a plurality of ECUs  2  to  4  perform various controls in the vehicle by controlling these sensors A 1 , A 2  and actuators B 1 , B 2 . A test port Data Link Connector (DLC)  7  that enables connection of a scan tool (i.e., equivalent to an external device)  6  from the outside of the vehicle is provided for the communication line  5 . 
         [0025]    The scan tool  6  has a liquid crystal display  8 , a plurality of buttons  9 , a cable  10 , a connector  11 , etc., for example, and is used by a worker of a vehicle manufacturer or a dealer when the worker connects the connector  11  to the test port  7  of the communication line  5 . A plurality of buttons  9  may be, for example, an all delete button, a part delete button, an OK button and the like. 
         [0026]    ECU  2  answers the scan tool  6  with the information relevant to abnormality diagnosis, etc. according to a command inputted via the communication line  5  from the scan tool  6 . For example, a read-out of diagnosis information (i.e., Diagnostic Trouble Codes (DTC)) recorded on ECU  2  is performed by the scan tool  6 , as well as erasure, a warning light control in the vehicle, a read-out of Vehicle Identification Number (VIN), a status display of a warning light (i.e., Malfunction Indicator Light (MIL)) and the like. 
         [0027]    ECU  2  is provided with a microcomputer (i.e., microcomp.)  12 , a communication interface  13 , and Electrically Erasable Progammable Read-Only Memory (EEPROM)  14  as a nonvolatile storage device. The microcomputer  12  is provided with Central Processing Unit (CPU)  16  and Static Random-Access Memory (SRAM)  15  that serves as a backup Random Access Memory (RAM). 
         [0028]    The microcomputer  12  is provided with the memories (e.g. CPU  16 ), Read-Only Memory (ROM)  17 , RAM  18 , and SRAM  15  as the backup RAM, and various kinds of functions are realized according to a processing of CPU  16  that executes memorized programs in the memory. 
         [0029]    The microcomputer  12  functions, for example, as an abnormality determiner, a reception unit (e.g., receptor), and a clearing unit (e.g., clearer) by the execution of the memorized programs. The contents of RAM  18  may be erased when an ignition switch  19  is turned off, which interrupts a power supply from a battery  20  to RAM  18 , and enables the reservation of a workspace at the time of execution of the program by CPU  16 . 
         [0030]    SRAM  15  is a volatile memory that continuously receives a power supply from the battery  20 , and keeps the memory contents without being affected by a turn ON and OFF of the ignition switch  19 . 
         [0031]    SRAM  15  is used as an area for memorizing the abnormality related information. SRAM  15  is provided with a readiness storage area (i.e., a first storage)  21  that memorizes readiness, a history information storage area (an equivalent for the second storage)  22 , and an abnormality related information storage area  23  that memorizes the diagnosis information (e.g., DTC) including the data when diagnosing an abnormality, or the like. In the drawing, the abnormality related information storage area  23  is shortened to “abnormality info. storage,” the history information storage area  22  is shortened to “history info. storage,” and the readiness storage area  21  is shortened to “readiness storage.” 
         [0032]    The readiness storage area  21  stores a readiness flag (i.e., abbreviated to “readiness” in the following description) that shows whether an abnormality diagnosis has been executed (i.e., completion/non-completion) for each type of abnormality diagnosis process that is performable by ECU  2 . 
         [0033]    The readiness (i.e., the storage of readiness) is the information that shows a completion of an abnormality diagnosis determination item or an abnormality diagnosis examination item (i.e., collectively abbreviated as an abnormality diagnosis item hereafter). 
         [0034]    For example, according to the OBD II standard, many items are prefixed as a continuous monitor object and a regular (i.e., intermittent) monitor object. 
         [0035]    As an item for the continuous monitoring, a misfire, a fuel system, an exhaust gas control system (i.e., an Air/Fuel (A/F) sensor), etc., may be included, and as an item for a regular monitoring, an exhaust gas recirculation system, an O2 sensor and its heater, a catalyst device, an evaporative gas discharge control device (i.e., an evaporation system), a secondary air supply system, an air conditioning system, etc. are included. 
         [0036]    When the abnormality diagnosis of each of these items is performed, and the diagnosis of each of the abnormality diagnosis items is completed by the microcomputer  12 , the microcomputer  12  memorizes completion of readiness in the readiness storage area  21  of SRAM  15 . 
         [0037]    The history information storage area  22  is an area that memorizes an abnormality diagnosis history (i.e., a normal history/an abnormal history) at an execution time of abnormality diagnosis processes, and the storage area  22  is provided in a corresponding manner to each type of the abnormality diagnosis processes regarding which the readiness is stored in the storage area  21 . The abnormality diagnosis history may either be (i) a normal diagnosis history, or a normal history (i.e., a normal diagnosis result indicating that the abnormality diagnosis item is determined as normal) or (ii) an abnormal diagnosis history, or an abnormal history (i.e., an abnormal diagnosis result indicating that the abnormality diagnosis item is determined as abnormal). 
         [0038]    The abnormality related information storage area  23  is provided as an area that stores and memorizes (i.e., keeps), abnormality diagnosis related information as the data in which an execution result of abnormality diagnosis is shown corresponding to readiness. The abnormality diagnosis related information represents, for example, that, as a result of diagnosis of each of the abnormality diagnosis items, i) abnormality found/exist, ii) no abnormality found/exist, iii) existence of abnormality unknown, and, when the diagnosis abnormality related information is in a reset condition, the information represents “existence of abnormality unknown”. 
         [0039]    EEPROM  14  is a nonvolatile memory provided with a Permanent Diagnosis Information (PDTC) storage area  24  for memorizing PDTC as the information which should be permanently or everlastingly memorized from among the diagnosis information (e.g., DTC). 
         [0040]    The microcomputer  12  performs a predetermined vehicle control by executing the program memorized in the memory, and performs the abnormality diagnosis about the vehicle control in parallel. Although the execution timing of the abnormality diagnosis process is different depending on the types of abnormality diagnosis, the microcomputer  12  may perform the diagnosis process immediately after a turn ON of the ignition switch  19  at a vehicle start time, based on an output signal of the various sensors, or may perform the abnormality diagnosis process at the vehicle travel time based on an execution result of the vehicle control. 
         [0041]    Further, even while the ignition switch  19  is turned OFF, using a soak timer (not illustrated), the microcomputer  12  may be started and the abnormality diagnosis process may be performed. The microcomputer  12  may also perform the abnormality diagnosis process based on the comparison between a previous vehicle state (i.e., an output signal from various sensors, etc.) and a current vehicle state (i.e., an output signal from various sensors, etc.), both of which may be stored in SRAM  15 , across a transition of driving cycles (i.e., when the ignition switch  19  is once turned OFF and then turned ON again) causing a transition of one driving cycle to the next cycle. 
         [0042]    In other words, among many diagnosis items, some items take relatively-long time to diagnose, which means such items are difficult to diagnose, while other items take only a short time to diagnose. The long diagnose time required items are, for example, items related to a fuel injection system. That is, when a complicated or rare condition has to be satisfied for driving an injector in terms of diagnosis of certain item, such an assumption may be hard to realize, and the detection or determination of an abnormality of the injection under such drive condition may be difficult than other abnormalities. More practically, when a misfire is caused, a history of such abnormality, or more specifically, a history of how an abnormal condition is caused is memorized as the abnormal history, and, when such an abnormal history is stored in a memory, an item that determines whether a next misfire is caused or not based on a condition that an engine rotation number is within a misfired number range may relatively be hard to diagnose. This is because of a rarity of realizing a base condition. In this case, the engine rotation number to enter into a misfired number range again, and, while the base condition is not satisfied, the diagnosis of such item cannot be performed. 
         [0043]    Further, a diagnosis item having the following operation scenario is also relatively difficult to diagnose. That is, after a continuation of constant speed travel of certain speed range (e.g., 40-50 km/h) for 10 seconds, an engine idle period is continued for a preset period (e.g., 60 seconds), which is a base condition of diagnosis, if a temperature sensor A 1  for detecting an engine coolant temperature detects an over-threshold temperature change, such an outcome is diagnosed as a normal operation of the sensor A 1 , and, if the sensor A 1  detects a less-than-threshold temperature change in the same situation, such an outcome is diagnosed as an abnormal operation of the sensor A 1 . The difficulty of diagnosis of the above item comes also from the rarity of the base condition (i.e., a simultaneous satisfaction of (i) a certain travel time at a certain speed and (ii) an engine idle period of preset time amount), which depends on a vehicle travel state and the like. Further, another difficult to diagnose item may be the one in which an abnormality diagnosis process is performed after a couple of hours from turning OFF of the ignition switch  19 , during which no user operation is performed. 
         [0044]    ECU  2  may be intermittently self-started for performing the abnormality diagnosis process after detecting a turning OFF of the ignition switch  19  by using a soak timer at a preset interval of a couple of hours or a couple of days. However, an abnormality diagnosis item of two conditions (i.e., (i) a first condition satisfied during an engine start time (i.e., at a previous start time for starting ECU  2 ) and (ii) a second condition, which is different from the first condition, satisfied during an engine stop time (i.e., at a present start time for starting ECU  2 ), may also be difficult to diagnose). 
         [0045]    For example, a normal determination based on the following two conditions may be difficult. That is, the normal determination is based on (i) a first condition; when a temperature detection result of the temperature sensor A 1  during an engine start time is equal to or greater than a first preset value (e.g., 40 degrees), and, (ii) a second condition; thereafter having no user operation after a stop of the engine and a detection result of water temperature sensor is less than a second preset value (e.g., 20 degrees). This is difficult to diagnose because it takes relatively long time to satisfy those conditions. Further, an item that requires a detection of a temperature change of an intake air besides detecting a temperature change of the engine coolant may also be relatively difficult to diagnose. 
         [0046]    For performing an abnormality diagnosis process during an engine stop time without user operation, ECU  2  may be started by a soak timer during such time, and ECUS  2  to  4  are intentionally driven to control the actuators B 1 , B 2  (e.g., for driving a heater of an air-fuel ratio (A/F) sensor, a heater of an O2 oxygen (O2) sensor, or a purge valve). That is, the abnormality diagnosis items that require actuator operations (i.e., actuators B 1 , B 2 ) without user intervention may also be “difficult” items. Such items typically require several hours to several days of diagnosis time, and items other than the above may take only a short time to diagnose, which makes it easy to detect abnormality for those items. 
         [0047]    The microcomputer  12  sets the readiness, which indicates completion of diagnosis of each of the various diagnosis items, to the readiness storage area  21  of SRAM  15 , as the information which shows that the abnormality diagnosis has been performed and is complete. Then, the microcomputer  12  updates the contents of the abnormality diagnosis related information in SRAM  15  by the contents of the abnormality diagnosis result of the relevant diagnosis. Further, when an abnormality is caused, an alarm display lamp (not illustrated) is turned ON, for example, by the microcomputer  12 , for reporting the abnormality to the occupant of the vehicle. 
         [0048]    Further, when the scan tool  6  is connected to the communication line  5 , an external request acceptance process is performed. In other words, when the microcomputer  12  stands by until receiving a certain request from the external device via the communication interface  13 , and when a request signal is received, it performs a relevant process according to the received signal. 
         [0049]    The output of the scan tool  6 , or an external device, is used to instruct ECU  2  to clear the readiness memorized in SRAM  15  (i.e., is a code clear request to ECU  2 ). The code clear request is a command outputted towards the microcomputer  12  according to the user&#39;s operation of the scan tool  6 , and one code clear request is output from the scan tool  6 , for example, according to one button operation on the tool  6  by the user. 
         [0050]    Hereafter, the action concerning the present embodiment is described. 
         [0051]    The process of the microcomputer  12 , when performing an abnormality diagnosis about vehicle controls, is illustrated in  FIG. 2  as a flowchart. The process shown in  FIG. 2  is performed for each of the abnormality diagnosis items. As shown in  FIG. 2 , for every abnormality diagnosis execution time, the microcomputer  12  determines whether a normal history exists in the history information storage area  22  (S 1 ), and, when a normal history exists, or when the normal history is stored previously in the history information storage area  22  (S 1 :YES), the microcomputer  12  determines whether a relaxed condition of an abnormality diagnosis item is satisfied (S 2 ) (i.e., in  FIG. 2 , an “eased condition” is used instead of relaxed). 
         [0052]    When the microcomputer  12  performs an abnormality diagnosis using a relaxed condition, which is more easily satisfied than a standard condition, and the relaxed condition is satisfied (S 2 :YES), readiness is considered as complete (S 3 ). After performing Step S 3 , the microcomputer  12  clears a normal history of this abnormality diagnosis item (S 4 ). 
         [0053]    On the other hand, the microcomputer  12  performs a normal abnormality diagnosis without using the relaxed condition (S 5 -S 9 ), when no normal history exists, the microcomputer  12  is without normal history that is stored previously in the history information storage area  22  (S 1 :NO). When performing the normal abnormality diagnosis (S 5 -S 9 ), the microcomputer  12  determines whether an abnormal condition of the abnormality diagnosis item is satisfied (S 5 ), and, if the abnormal condition is satisfied (S 5 :YES), the microcomputer  12  clears the normal history in the history information storage area  22  (S 6 ). Satisfaction of the abnormal condition means that an abnormal operation of the sensors A 1 , A 2 , etc. is confirmed. 
         [0054]    On the contrary, when performing the abnormality diagnosis, upon determining that a normal condition is satisfied (S 7 :YES), the microcomputer  12  keeps (i.e., stores and memorizes) the satisfaction of the normal condition as a normal history to the history information storage area  22  (S 8 ). Satisfaction of the normal condition means that a normal operation of the sensors A 1 , A 2  etc., is confirmed. 
         [0055]    Further, the microcomputer  12  considers that readiness is complete, when either of the normal condition or the abnormal condition of the abnormality diagnosis item is satisfied (S 9 ). 
         [0056]    Further, when readiness is incomplete after NO in Step S 7  of  FIG. 2  (S 10 :YES), the microcomputer  12  considers that readiness is complete upon having YES in S 11  of  FIG. 3 , which means that the relaxed condition of the abnormality diagnosis item is satisfied, and sets that readiness is complete (S 12 ), and clears the normal history (S 13 ). Otherwise, the process is finished (S 10 :NO or S 11 :NO). 
         [0057]    Hereafter, an example is described. When the ignition switch  19  of the vehicle is turned ON, the engine starts and is put in a warm-up state. CPU  16  of the microcomputer  12  detects that a first prescribed time (e.g., a certain number of seconds) has passed after the start of the engine by using a timer (not shown), for example, and determines whether a travel distance is equal to or greater than a first prescribed distance. In case that no abnormal state is caused even after these prescribed conditions are satisfied, CPU  16  determines that the normal condition is satisfied (S 7 :YES), and stores, to SRAM  15 , history information that the normal history exists (S 8 ). 
         [0058]    Although satisfaction of the “prescribed conditions” is determined only once (i.e., in one cycle) in the above-described example, satisfaction of the prescribed conditions (i.e., after a first prescribed time from a start of an engine, and a travel distance is equal to or greater than a first prescribed distance) may be repeatedly determined many times for determining that the normal condition is satisfied. 
         [0059]    Then, the microcomputer  12  performs the abnormality diagnosis with the application of the relaxed condition at the time of performing the next abnormality diagnosis (i.e., S 1 -S 4  in the next cycle). The relaxed condition in the next cycle may be a second prescribed time, which is configured to be smaller than the first prescribed time, and a second prescribed distance, which is smaller than the first prescribed distance. 
         [0060]    Since the microcomputer  12  determines that, as history information, the normal history exists (S 1 :YES), in case that the no abnormal state is caused even after the second prescribed time from a start of the engine and at a travel distance equal to or greater than the second prescribed distance, it is determined that the relaxed condition is satisfied (S 2 :YES), and that readiness is complete (S 3 ). Then, the normal history memorized in SRAM  15  is cleared (S 4 ). In such manner, when the relaxed condition of the abnormality diagnosis is satisfied, readiness is considered as complete. 
         [0061]    According to the above, when the normal history exists, the diagnosis of the abnormality is performed by using the relaxed condition for the abnormality diagnosis items, and upon determining that the relaxed condition is satisfied, the readiness is considered as complete. That is, it does not take a long time to complete readiness (i.e., ease of readiness completion is achieved). 
         [0062]    The relaxed condition may be set in various ways/manners other than the above-described example, and relaxed condition may be applicable to what kind of abnormality is configured in advance. Further, the relaxed condition of the abnormality diagnosis item may be uniformly determined for the entire system as a single condition, or may be determined as respectively different conditions item to item. 
         [0063]    Further, when the relaxed condition of the abnormality diagnosis item is not satisfied (S 2 :NO), the microcomputer  12  considers that readiness is complete (S 9 ) when the abnormal condition of the abnormality diagnosis item is satisfied (S 5 :YES), or when the normal condition of the abnormality diagnosis item is satisfied (S 7 :YES). 
         [0064]    As described above, according to the present embodiment, when performing the abnormality diagnosis of a vehicle, the microcomputer  12  uses the relaxed condition, (i.e., an easily-satisfied condition), of the abnormality diagnosis item for a determination that readiness is complete (S 2 ) in case that the history information in the history information storage area  22  has the normal history. Therefore, the completion of readiness is easily achievable. Further, even when the satisfaction of the condition of the abnormality diagnosis/inspection item takes a long time, or is difficult, readiness becomes easily storable in the readiness storage area  21  according to the above. Therefore, the readiness completion process is facilitated and the user of the vehicle receives a service more quickly. 
         [0065]    Further, if the history information memorized in the history information storage area  22  indicates that no normal history exists when the microcomputer  12  performs the abnormality diagnosis of a vehicle, the abnormality diagnosis is performed without using a relaxed condition of the abnormality diagnosis item. This means that the abnormality of a vehicle is discovered according to a normal flow of abnormality diagnosis. 
         [0066]    Further, if the history information memorized in the history information storage area  22  indicates that the normal history exists (S 1 :YES), the microcomputer  12  may consider that readiness is complete (S 3 ) when the relaxed condition of the abnormality diagnosis item is satisfied (S 2 :YES), and, when the relaxed condition of the abnormality diagnosis item is not satisfied (S 2 :NO), the microcomputer  12  may consider that readiness is complete (S 9 ) (i) when the abnormal condition of the abnormality diagnosis item is satisfied (S 5 :YES) or (ii) when the normal condition of the abnormality diagnosis item is satisfied (S 7 :YES), leading to a determination that readiness in the readiness storage area  21  is complete. 
         [0067]    The microcomputer  12  may determine satisfaction/non-satisfaction of the abnormal condition and the normal condition of the abnormality diagnosis item, and may clear the normal history when the abnormal condition is satisfied (S 6 ), or may keep the normal history (i.e., may keep the history information that indicates that the normal history exists), when the normal condition is satisfied (S 8 ). 
       Second Embodiment 
       [0068]      FIG. 4  is an additional diagram (i.e., a flowchart) of the second embodiment. The second embodiment describes a process at the time of receiving a code clear request. The scan tool  6  is capable of outputting a code clear request to ECU  2 . The code clear request is a command outputted toward the microcomputer  12  according to an operation of the button  9  of the scan tool  6  by a user, and one code clear request is output by one operation of the button  9  of the scan tool  6  by the user, for example. In the present embodiment, the microcomputer  12  executes a program memorized by the memory, and serves as an abnormality determiner, a reception unit, and a clearing unit. 
         [0069]    When the scan tool  6  outputs a code clear request to ECU  2  according to the user&#39;s operation, the microcomputer  12  of ECU  2  receives the code clear request (T 1 :YES). Then, the microcomputer  12  determines whether the relaxed condition of the abnormality diagnosis item (i.e., an eased condition) is satisfied (T 2 ). When the eased condition is satisfied (T 2 :YES), the normal history in the history information storage area  22  is cleared (T 3 ). When the eased condition is not satisfied (T 2 :NO), the process is finished, without clearing the normal history in the history information storage area  22 . 
         [0070]    According to the present embodiment, even when the microcomputer  12  receives a code clear request, the normal history is cleared based further on a certain condition (i.e., when the eased condition is satisfied), and the normal history is not cleared when the eased condition is not satisfied. In other words, such a clearing scheme makes it harder to perform the clearing of the normal history in the history information storage area  22 , thereby making it unnecessary to re-establish the normal history (i.e., time to re-diagnose the abnormality diagnosis item(s) to record the normal history is not required). 
       Third Embodiment 
       [0071]      FIG. 5  is an additional diagram (i.e., a flowchart) of the third embodiment. The third embodiment describes a modification of the second embodiment. According to the present embodiment, the microcomputer  12  executes a program memorized by the memory, and serves as a component functioning as the abnormality determiner, the reception unit, and the clearing unit. 
         [0072]    As shown in  FIG. 5 , when the scan tool  6  outputs a code clear request to ECU  2  according to the user&#39;s operation, the microcomputer  12  of ECU  2  determines whether the microcomputer  12  has received a code clear request (T 1 ), and, based on the number of receptions of the code clear request (i.e., when the number of receptions of the code clear request reaches a threshold (T 1   a :YES)), the microcomputer  12  clears the normal history in the history information storage area  22  (T 3 ). The microcomputer  12  concludes the process without clearing the normal history when the number of receptions of the request is other than the above (T 1 , T 1   a :NO). 
         [0073]    As shown in the present embodiment described above, the normal history may be cleared based on a condition of the number of receptions of the code clear request received by the microcomputer  12 , and the normal history may be not cleared based on a condition other than the above. 
       Fourth Embodiment 
       [0074]      FIG. 6  is an additional diagram (i.e., a flowchart) of the fourth embodiment. The fourth embodiment describes a transition process of transitioning a driving cycle. According to the present embodiment, the microcomputer  12  executes a program memorized by the memory, and serves as a component functioning as the abnormality determiner, a driving cycle determiner, and the clearing unit. 
         [0075]    As shown in  FIG. 6 , the microcomputer  12  determines whether the driving cycle has transitioned (U 1 ). The driving cycle is a cycle that transitions when an operation of a vehicle is started (e.g., when the ignition switch  19  is turned from OFF to ON). 
         [0076]    When it is determined by the microcomputer  12  that the ignition switch  19  is turned from OFF to ON, it is determined that a driving cycle has transitioned (i.e., has changed) (U 1 ). 
         [0077]    When the microcomputer  12  determines that the driving cycle has transitioned (U 1 :YES), the microcomputer  12  then determines whether the relaxed condition of the abnormality diagnosis item (i.e., an eased condition) is satisfied (U 2 ). 
         [0078]    When the eased condition is satisfied in the above determination, the microcomputer  12  clears the normal history in the history information storage area  22  (U 3 ). When the eased condition is not satisfied (U 2 :NO), the process is finished, without clearing the normal history in the history information storage area  22 . 
         [0079]    According to the present embodiment, when the microcomputer  12  determines that the driving cycle has transitioned to the next driving cycle, and when the transition to the next driving cycle is determined, the microcomputer  12  clears the normal history based on a condition that the eased condition is satisfied. This means that, when the eased condition is not satisfied, the normal history is not cleared. That is, the normal history may be kept non-cleared/un-erased until the driving cycle transitions, as shown in the present embodiment. 
         [0080]    In addition, when the history information storage area  22  is provided in RAM  18  etc. (not illustrated), after a turning OFF of the ignition switch  19 , for example (i.e., during an engine stop time), the normal history of the abnormality diagnosis item memorized in the history information storage area  22  is held (i.e., is kept non-cleared/un-erased). 
       Fifth Embodiment 
       [0081]      FIGS. 7 and 8  show additional diagrams (i.e., flowcharts) of the fifth embodiment. 
         [0082]    The fifth embodiment is a modification of the fourth embodiment. According to the present embodiment, the microcomputer  12  executes a program memorized by the memory, and serves as a component functioning as the abnormality determiner, the driving cycle determiner, and the clearing unit. 
         [0083]    As shown in  FIG. 7 , the microcomputer  12  determines whether the driving cycle has transitioned (change) (U 1 ), and, based on a condition that the driving cycle has transitioned by a preset number of times (e.g., 10 times) (U 1   a :YES), clears the normal history in the history information storage area  22  (U 3 ). 
         [0084]    The microcomputer  12  finishes the process without clearing the normal history in the history information storage area  22 , when the condition is other than the above (U 1 :NO or U 1   a :NO). 
         [0085]    According to the present embodiment, the microcomputer  12  clears the normal history based on a condition that the driving cycle has transitioned by a preset number of times in total, and does not clear the normal history in other cases. In other words, the normal history may be kept non-cleared/un-erased until the driving cycle transitions by a preset number of times, as described in the present embodiment. 
         [0086]    By implementing the above-described normal history clearing scheme, a reliability of the information stored in the history information storage area  22  is improved, because, after a certain number of transitions of the driving cycle, it is highly possible that the vehicle state (i.e., a normal or an abnormal state of the sensors A 1 , A 2 ) has been changed. That is, by clearing the falsely “optimistic” normal history, the stored information regarding the abnormality diagnosis becomes more reliable. 
         [0087]    In addition, when the history information storage area  22  is provided in RAM  18 , etc. (not illustrated), after a turning OFF of the ignition switch  19 , for example (i.e., during an engine stop time), the normal history of the abnormality diagnosis item memorized in the history information storage area  22  is held (i.e., is kept non-cleared/un-erased) as long as possible. 
         [0088]    Further, a determination step for determining whether the eased condition is satisfied (i.e., Step U 2  in  FIG. 6 ) may be inserted at a certain position ahead of Step U 3  in  FIG. 7 . By inserting U 2  of  FIG. 6  into such a position, the reliability of the memory contents in the history information storage area  22  is improved/assured according to the following logic. That is, when the eased condition is not satisfied (U 2 :NO) after many transitions of the driving cycle (i.e., after a travel of the vehicle for a long distance), the normal history in the memory may possibly be a false positive (i.e., may be not reliable). Therefore, such false positive memory contents in the storage area  22  would better be cleared for the improved reliability of the memory contents. 
       Sixth Embodiment 
       [0089]      FIG. 9  is an additional diagram, (i.e., a flowchart), of the sixth embodiment. Since the sixth embodiment is a modification of the second embodiment or the third embodiment, the step numbers of T 1  T 1   a -T 3  of  FIGS. 4 and 5  are borrowed and are used in  FIG. 9 . According to the present embodiment, the microcomputer  12  executes a program memorized by the memory, and serves as a component functioning as the abnormality determiner, the reception unit, a timer, and a counter. 
         [0090]    As shown in  FIG. 9 , the microcomputer  12  of ECU  2  receives a code clear request when the scan tool  6  outputs a code clear request to ECU  2  (T 1 ). The code clear request is a command that is outputted once according to one depression of the button  9  which may be a request button or a confirmation button and is outputted once again according to one depression of the button  9  (e.g., of the confirmation button or the like). 
         [0091]    When receiving the code clear request, the microcomputer  12  measures a time from such a reception of the code clear request by using a timer (not illustrated), and determines whether an interval between the two requests (i.e., from the previous request to the current request) is less than a preset number of seconds (T 10 ). 
         [0092]    Further, the microcomputer  12  increments the counter (+1) (T 11 ) when a T 10  condition is satisfied (T 10 :YES), and determines whether the number of code clear requests reaches a preset value of threshold (T 1   a ). 
         [0093]    The microcomputer  12  clears the normal history in the history information storage area  22  (T 3 ), when the number of requests reaches the preset value (T 1   a :YES). On the other hand, the microcomputer  12  does not clear the normal history in the history information storage area  22 , when the reception of the code clear requests is not within the preset number of seconds from the previous request (T 10 :NO) or when the number of requests has not reached the preset value of threshold (T 1   a :NO). Further, when the reception of the code clear request is not within the preset number of seconds from the previous request (T 10 :NO), the microcomputer  12  clears the number of code clear requests (i.e., the microcomputer  12  resets the counter that counts the number of code clear requests (T 12 )). 
         [0094]    According to the present embodiment, the microcomputer  12  measures a time between two code clear requests (i.e., from the reception of the previous code clear request to the reception of the current code clear request), and based on a condition that the measured time is within a preset amount of time, the reception of the current code clear request is validated (i.e., increment the counter counting the requests). Then, based on the present number of requests in total, the normal history in the history information storage area  22  is cleared, and the normal history is not otherwise cleared. That is, when the above-described conditions are not satisfied, the normal history is not cleared. 
       Other Embodiments 
       [0095]    The above-mentioned embodiments may further be modified or expanded. 
         [0096]    Although, in the above-mentioned embodiments, varieties of information (e.g., readiness, the history information, the abnormality diagnosis related information, etc.) is stored in SRAM  15 , which functions as a backup RAM, such information may be stored in other memories (e.g., in a normal RAM  18 ), a non-volatile memory (e.g., EEPROM) other than the above. 
         [0097]    Although the present disclosure has been described in connection with preferred embodiment thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art, and such changes, modifications, and summarized scheme are to be understood as being within the scope of the present disclosure as defined by appended claims.