Patent ID: 8441263

Claim:
A voltage monitor for monitoring a voltage of a battery relative to a monitor threshold and for diagnosing the monitor threshold based on each of a first diagnostic threshold and a second diagnostic threshold, the voltage monitor comprising: a first obtaining unit configured to obtain a first relative relationship between the battery voltage and one of the monitor threshold and the first diagnostic threshold and to output first information indicative of the first relative relationship; a second obtaining unit configured to obtain a second relative relationship between the battery voltage and one of the monitor threshold and the second diagnostic threshold and to output second information indicative of the second relative relationship; a threshold switching unit configured to stepwisely switch, by a constant level, a level of each of the first and second diagnostic thresholds when each of the first and second diagnostic thresholds is used by a corresponding one of the first and second obtaining units; a first forced-output unit configured to forcibly output a first forced signal when a preset period of time has elapsed since a start of the stepwise switch of the first diagnostic threshold by the threshold switching unit; a second forced-output unit configured to forcibly output a second forced signal when the preset period of time has elapsed since a start of the stepwise switch of the second diagnostic threshold by the threshold switching unit; and an abnormality detecting unit configured to: receive the first information outputted from the first obtaining unit and the second information outputted from the second obtaining unit; determine that an abnormality that affects on at least one of the first and second diagnostic thresholds arises in the voltage monitor when the first information is different from the second information; receive the first forced signal outputted from the first forced-output unit and the second forced signal outputted from the second forced-output unit; and determine whether a timing at which the level of the first diagnostic threshold is switched for each step is deviated from a timing at which the level of the second diagnostic threshold is switched for a corresponding step based on a result of a comparison between the first forced signal and the second forced signal.