Preparation for Test: 1. Review 11 , 2. Check actual configuration of the control modules as located in the vehicle using the HHT, 3. Connect HHT (see section 0) and read out DTC codes. (Use Star Diagnosis System for Model 220).

Test equipment; See MBUSA Standard Service Equipment Program

Description	Brand, model, etc.
Digital multimeter	Fluke models 23, 77 III, 83, 85, 87

DTC	Possible cause	Test step/Remedy 1)
No fault code	No DTC recognized. In case of complaint: 13 (entire test).	13
	Fiber optic cable defective. The transmitter of one of the control modules defective, The receiver of one of the control modules defective. (No data transmission between Radio or COMAND and control module in position X is possible).	See 11/5
	Fiber optic cable defective. The transmitter of one of the control modules defective, The receiver of one of the control modules defective. (No data is transmitted between Radio and component located prior to D2B Interface).	See 11/5
	Fiber optic cable defective. The transmitter of one of the control modules defective, The receiver of one of the control modules defective. (Data transfer/transmission is faulty).	See 11/5
	Head unit can not be integrated into D2B Ring-Loop Initialization of D2B is faulty. (Erase DTC readout codes, switch on entire system and then readout DTC fault codes again.	If fault continues to show, swap out head unit.
	Due to faulty Initialization, a control module can not be integrated into a position within D2B Ring-Loop D2B Initialization of the control module is faulty: Readout DTC memory, switch-on entire system and then readout DTC fault codes again.	See 11/5, if fault continues to show, swap out effected control module.
	D2B component has failed at its position within D2B Ring-Loop (bypass-mode). Internal fault of the control module located in that position. Erase DTC memory, switch-on entire system and then readout DTC fault codes again.	See 11/5
	D2B Initialization of a D2B component is faulty. Erase DTC memory, switch-on entire system and then readout DTC fault codes again.	There are also faults within other control modules that are within D2B Ring-Loop: Swap Head Unit. There are no faults within other control modules that are within D2B Ring-Loop: Swap control module.
	D2B Initialization of a D2B component is faulty. Erase DTC memory, switch-on entire system and then readout DTC fault codes again.	There are also faults within other control modules that are within D2B Ring-Loop: Swap Head Unit. There are no faults within other control modules that are within D2B Ring-Loop: Swap control module.
	Radio: The "Should Be" and actual configuration of the D2B Ring-Loop vary.	Re-configure system again.

1) Observe Preparation for Test