| Fault location | Group convenience data bus | Control unit in the dash panel insert -J285- | Central control unit for the convenience system -J393- |
| Type of fault | Fault | In one-wire operating mode | Messages missing | No communication | Read out fault memory | No communication | Read out fault memory |
| Possible cause of fault | | | | | | | |
| Both signal wires interrupted | X | | X | X | | X | |
| Short circuit on or between both signal wires | X | | X | X | | X | |
| The two signal wires have been interchanged | X | | X | | | | |
| One of the two signal wires interrupted | | X | | | | | |
| Short circuit on one of the two signal wires | | X | | | | | |
| Open circuit in earth connection or voltage supply to this control unit | | | | X | | X | |
| Fault in a control unit connected to the data bus system | X | X | | X | | X | |
| Fault on the drive data bus system | | | X | | X | | X |
| Fault in a component upstream of this control unit | | | | | X | | X |
| Control unit not encoded as specified | | | | X | | X | |
| Control unit adaption not as specified | | | | X | | X | |
| Control unit data levels do not match (wrong control unit installed) | X | | X | X | | X | |
