Patent Number: 
Section: claims

1. A method for investigating a cause of decrease in frequency of abnormality detections for a certain device mounted on a vehicle, wherein when a plurality of abnormality detection conditions are satisfied, an abnormality detection for the certain device is performed to determine if the certain device is in failure, the method comprising:(i) when the frequency of the abnormality detections is below a predetermined value, disabling one of the abnormality detection conditions;(ii) when the abnormality detection conditions except the disabled abnormality detection condition are satisfied, performing an abnormality detection for the certain device;(iii) repeating the step (ii) a plurality of times; and(iv) determining if the disabled abnormality detection condition at that time is the cause of the decrease in the frequency of the abnormality detections, based on frequency of the abnormality detections in the step (iii). 2. The method according to claim 1, further comprising:(v) if the determining in the step (iv) is negative, enabling the disabled one of the abnormality detection conditions and disabling another one of the abnormality detection conditions; and(vi) repeating the steps (ii) to (v). 3. The method according to claim 2, wherein the step (vi) is performed until the cause of the decrease in the frequency of the abnormality detections is found. 4. The method according to claim 2, wherein:the disabling of the step (i) comprises rewriting the one of the abnormality detection conditions so as to be always satisfied; andthe disabling of the step (v) comprises rewriting the another abnormality detection condition so as to be always satisfied. 5. The method according to claim 2, wherein:the disabling of the step (i) comprises rewriting the one of the abnormality detection conditions so as to be satisfied more easily than that before the rewriting of the step (i); andthe disabling of the step (v) comprises rewriting the another abnormality detection condition so as to be satisfied more easily than that before the rewriting of the step (v). 6. The method according to claim 2, wherein in the step (v), the one of the abnormality detection conditions is higher in possibility of the cause of the decrease in the frequency of the abnormality detection than the another one of the abnormality detection conditions. 7. The method according to claim 1, wherein the step (iv) comprises:comparing the frequency of the abnormality detections in the step (iii) with the frequency of the abnormality detections before the method is performed; anddetermining if the disabled abnormality detection condition at that time is the cause of the decrease in the frequency of the abnormality detections based on a comparing result. 8. The method according to claim 1, wherein the disabling of the step (i) comprises rewriting the one of the abnormality detection conditions so as to be always satisfied. 9. The method according to claim 1, wherein the abnormality detection conditions form a plurality of hierarchic layers each comprising a plurality of conditional statements, the method further comprising:rewriting a program for determining whether or not the abnormality detection conditions are satisfied so as to add to a conditional statement of each hierarchic layer a statement, which sets a monitor flag to ON or OFF; andidentifying which hierarchic layer comprises the cause of the decrease in the frequency of the abnormality detections, wherein:the rewriting and the identifying are performed before the step (i). 10. The method according to claim 1, wherein the disabling of the step (i) comprises rewriting the one of the abnormality detection conditions so as to be satisfied more easily than that before the rewriting. 11. The method according to claim 1, wherein the step (iii) comprises turning on and off an ignition switch of vehicle the plurality of time. 12. The method according to claim 11, wherein the frequency of the abnormality detections for the certain device is defined as a value obtained by dividing an actual frequency of the abnormality detections for the certain device within a predetermined time period by number of times the ignition switch of the vehicle is turned on within the predetermined time period. 13. A method for improving frequency of abnormality detections comprising:after the method according to claim 1 is performed, rewriting an abnormality detection condition, which has been determined as the cause of the decrease in the frequency of the abnormality detections for the certain device, so as to be satisfied more easily than that before the rewriting. 14. A method for improving frequency of abnormality detections comprising:after the method according to claim 1 is performed, disabling an abnormality detection condition, which has been determined as the cause of the decrease in the frequency of the abnormality detections for the certain device. 15. The method according to claim 1, further comprising:when the cause of the decrease in the frequency of the abnormality detections for the certain device is found, transmitting the cause to a center. 16. A method for improving frequency of abnormality detections comprising:after the method according to claim 1 is performed, transmitting to a center an abnormality detection condition, which has been determined as the cause of the decrease in the frequency of the abnormality detections for the certain device; anddisabling the transmitted abnormality detection condition by the center, to temporarily increase the frequency of the diagnosis detections. 17. A method for improving frequency of abnormality detections comprising:after the method according to claim 1 is performed, transmitting to a center an abnormality detection condition, which has been determined as the cause of the decrease in the frequency of the abnormality detections for the certain device; andrewriting the transmitted abnormality detection condition by the center so that the rewritten abnormal detection condition is satisfied more easily than that before the rewriting, to thereby temporarily increase the frequency of the diagnosis detections. 18. The method according to claim 1, wherein an abnormality detection master ECU that monitors ECUs for controlling the vehicle performs the method. 19. The method according to claim 1, wherein:in the step (i), when the frequency of the abnormality detections is below the predetermined value, an abnormality detection master ECU instructs another ECU whose frequency of the abnormality detections is determined to be decreased to investigate the cause of the decrease in the frequency of the abnormality detections; andthe another ECU performs the remaining steps. 20. The method according to claim 1, wherein respective ECUs perform the method. 21. A method for diagnosing a vehicle, the method comprising:(a) while the vehicle is running, performing the method of claim 1; and(b) while the vehicle is running, detecting an abnormality of the certain device. 22. The method according to claim 21, wherein the steps (a) and (b) are performed alternatively. 23. The method according to claim 21, wherein the steps (a) and (b) are performed simultaneously. 24. An electronic control apparatus for a vehicle, the apparatus comprising:an abnormal detecting unit that performs an abnormality detection based on a plurality of abnormality detection conditions, to determine if a certain device mounted on the vehicle is in failure; andan abnormality cause investigating unit that investigates a cause of decrease in frequency of the abnormality detections for the certain device, wherein:when the frequency of the abnormality detections is below a predetermined value, the abnormality cause investigating unit disables one of the abnormality detection conditions,when the abnormality detection conditions except the disabled abnormality detection condition are satisfied, the abnormal detecting unit performs an abnormality detection for the certain device; andthe abnormality cause investigating unit determines if the disabled abnormality detection condition at that time is the cause of the decrease in the frequency of the abnormality detections, based on the frequency of the abnormality detections performed by the abnormal detecting unit. 25. A method for investigating a cause of decrease in frequency of abnormality detections for a certain device mounted on a vehicle, wherein when a plurality of abnormality detection conditions are satisfied, an abnormality detection for the certain device is performed to determine if the certain device is in failure, the method comprising:(i) when the frequency of the abnormality detections is below a predetermined value, disabling the abnormality detection conditions except one of the abnormality detection conditions;(ii) when the one of the abnormality detection conditions is satisfied, performing an abnormality detection for the certain device;(iii) repeating the step (ii) a plurality of times;(iv) determining if the one of the abnormality detection conditions at that time is the cause of the decrease in the frequency of the abnormality detections, based on frequency of the abnormality detections in the step (iii);(v) enabling the abnormality detection conditions other than the one of the abnormality detection conditions while disabling the one of the abnormality detection conditions; and(vi) when the others of the abnormality detection conditions except the disabled one of the abnormality detection conditions are satisfied, performing an abnormality detection for the certain device;(vii) repeating the step (vi) a plurality of times; and(viii) determining if the disabled one of the abnormality detection conditions at that time is the cause of the decrease in the frequency of the abnormality detections, based on frequency of the abnormality detections in the step (vi). 26. A method for investigating a cause of decrease in frequency of abnormality detections for a certain device mounted on a vehicle, wherein when a plurality of abnormality detection conditions are satisfied, an abnormality detection for the certain device is performed to determine if the certain device is in failure, the method comprising:(i) when the frequency of the abnormality detections for the certain device is below a first predetermined value, disabling the abnormality detection conditions except one of the abnormality detection conditions, wherein abnormality detection conditions for another device whose frequency of abnormality detections is below a second predetermined value contains the one of the abnormality detection conditions;(ii) when the one of the abnormality detection conditions except the disabled abnormality detection conditions is satisfied, performing an abnormality detection for the certain device;(iii) repeating the step (ii) a plurality of times; and(iv) determining if the one of the abnormality detection conditions at that time is the cause of the decrease in the frequency of the abnormality detections, based on frequency of the abnormality detections for the certain device in the step (iii).