Vehicle diagnostic systems have been proposed which are based on the interrogation of a series of sensors located at critical points of the vehicle by an automatic check-out device which is a part of the service shop equipment. At least one system of this type already is in use on an imported passenger car. Systems also are in existence which provide a series of alarms to warn the operator of certain off-normal conditions which may occur during daily vehicle operation. Many off-normal conditions thus alarmed may never be reported because they are of a momentary or intermittent nature. This type of condition rarely can be detected by means of a checkout on the floor of the service shop. The diagnostic system described monitors off-normal conditions as they occur during day-to-day operation and provides a record of them for use by maintenance people. The simplest form of the system provides only a count of the number of occurrences. A more sophisticated form of the system provides a record of magnitude and duration with a real time base. A modified tachograph has been used in a basic system. A printer or magnetic recording also may be used.