Abstract: A method and device for diagnosing a vehicle, in which a forced activation signal Sx is supplied to a diagnostic target part through an ECU. A current state of the detected diagnostic target part is compared with a state predicted when the forced activation signal Sx is given to diagnose the diagnostic target part. The forced activation signal Sx when the diagnostic target part is judged to be good, or after a predetermined time has elapsed since issue of the signal Sx was initiated.

Abstract: Forced activation signal supplier 550 supplies a forced activation signal Sx to a diagnostic target part 101 related to a diagnostic item requiring a forced activation signal. Vehicle-state detector 552 detects a current state of the diagnostic target part 101 through an ECU 1. Diagnostic element 553 compares the currently detected state of the diagnostic target part 101 with a state predicted when the forced activation signal Sx is given to diagnose the diagnostic target part 101. When the forced activation signal Sx is supplied to the part of the vehicle, self-diagnosis stopping element 554 gives an instruction to stop a self diagnosis for at least an item the diagnostic result of which may vary under the influence of the forced activation signal Sx, or to invalidate the diagnostic result.

Abstract: There is provided vehicle diagnostic method and apparatus capable of reducing restrictions on the sequence and timing of operations to be performed by an operator for each diagnostic item.In the vehicle diagnostic apparatus, the actual vehicle state detected by the vehicle state detection apparatus 223 is compared with the expected state selected by the selection apparatus 222. For example, while the operator runs the vehicle on purpose to execute the "Vehicle Sensor Diagnosis", if an actual state (vehicle speed VS) is detected by the vehicle state detection apparatus 223, an expected state of the vehicle speed (reference vehicle speed VSref) will be selected by the selection apparatus 222. Then both states are compared by the comparison apparatus 224. When both states are identified as exhibiting an expected relation (e.g., correspondence), the comparison apparatus 224 makes the display 27 indicate that the diagnostic item 1 is passed. Specifically, the indication of "01" is erased from the display 27.