VEHICLE TROUBLE DIAGNOSIS SYSTEM

In an automotive failure diagnosing system configured to conduct malfunction diagnosing display by operating a lamp (5) in response to a CPU hang-up detection signal (WDA) output from a microcomputer (2) that monitors whether a control microcomputer (1) is hung up and to deliberately output a CPU hang-up detection signal (WDA) for malfunction diagnosis before the execution of control by the microcomputer (1) is commenced, a transistor (4A) is turned on to keep the lamp (5) continuously lit from the time that an ignition switch is switched from off to on to the time that a light-up operation for checking the lamp (5) is commenced, thereby preventing the lamp (5) from assuming a flickering condition when the lamp (5) is checked.