Vehicle fault diagnostic method using computer to check for faults in engine computer and air conditioning computer has also remote signaling of any faults found

摘要

The fault testing computer sends to onboard computers (15,16) a data request and receives responses which it processes, to determine the absence or presence of a fault in them (15,16). If a fault is detected the diagnostic computer transmits a signal to a remote center (20). A request for data is sent at least twice to the computers (15,16) and a response is received for each request, processing of the last one includes a comparison of this with the one previously received. A response message consists of a bit train. The comparison between two response messages is done on the same part of the bit train for each message response, by comparing the bit values of the two messages. Alternatively the comparison is made on the difference between the two parts of the bit train. The periodic signal sent by the diagnostic system to the remote center (20) includes at least a response message from the computers (15,16) for which a fault has been detected.