WHAT ISSUE are "we" trying to solve exactly? What Vehicle exactly?? If 335xi, that is a DSC/DXC, which is different variant from simple DSC on 335i. DSC NOT communicating with ISTA? DSC shown in RED on ISTA Control Unit Tree? Diagnostic software (ISTA/ INPA) are intended to be used BEFORE you disconnect every wiring connector in the vehicle.
IF DSC/DXC is NOT communicating with ISTA (Shown in RED on Control Unit Tree), then likely cause is either (1) lack of power supply (including ground) to DSC/DXC, or (2) Fault in PT-CAN lines between DSC/DXC and JBE. The JBE Module is the "Hub" to which BOTH the DSC/DXC and ISTA (through the OBD II Socket) connect. AFAIK, There is NO connection to DME that is pertinent to ISTA NOT Communicating with DSC/DXC Module.
Attached is a pdf describing HOW to use ISTA to obtain proper diagnostic information (which you can share via ScreenPrints as described on last page of pdf). If you want competent help from the Forum, please provide the following:
1) Last-7 Characters of the VIN of vehicle in question (necessary to provide correct wiring info);
2) ScreenPrints of:
a) Control Unit Tree or CU List;
b) Fault Memory List (click 'Display Fault Memory' button at bottom-right of CU Tree or CU List Screen);
c) If you would prefer to use INPA, ScreenPrints of Functional Jobs > F2 Identification & F4 Error Memory, ALL Modules;
3) Please identify any connectors or fuses that have been disconnected or removed.
4) Please identify any Warning Lights, or issues with components or systems, which are currently present.
With that information, we can BEGIN the Diagnosis.
George
