Information Bus Diagnosis and Testing

The Diagnostic Module may be used for diagnostic purposes if the I-Bus is suspected to be faulty. The EKM can detect if this circuit is open, shorted to power or ground, communication not possible with only one control unit or a fault with the data processing function itself. Defect codes for each of these conditions can be stored in the EKM and subsequently read out with the aid of the Diagnostic Module. Diagnostic procedures for these problems are included in both the diskettes and the Diagnostic Procedures Manual for the E31.

The I-Bus has an additional function for diagnostic purposes. All of the control units which are connected to this circuit do not have TxD and RxD leads as might be expected. Instead, diagnosis takes place through the EKM. For example, when the Diagnostic Module is used to investigate a problem with the ZKE II system, the data is sent from Service Tester to EKM by way of the TxD and RxD leads. The EKM retrieves the requested data from the General Module through the I-Bus. Diagnosis with the EKM is possible if either Terminal 30 or Terminal 15 is present.