Diagnosis bus defective

Disturbances in data transfer on the diagnostic bus (TxD link) may be attributed to the following faults:

Control unit emits interference

A control unit disturbs data traffic

• Briefly disconnect and connect battery. Then repeat test step ”test diagnostic bus 01”.
  
• No further measures are necessary if fault no longer occurs within the current diagnostic procedure.
  
• If the fault reoccurs, determine faulty control unit by removing one after the other the fuses of all control units connected to the diagnostic bus (refer to schematic). Repeat the test step ”test diagnostic bus 01” after each fuse.
  If data transfer to the other control units is OK, the control unit with no power applied will disturb data traffic. The control unit concerned should be replaced (refer to currently applicable Service Information. The fault may be in the software and can also occur with new control units).
  

Line faulty

The data link (TxD link) has a break or short to positive or ground

• Check line with ”preset measurement - line test” and repair if necessary.
  
• A short in the line may be caused by a faulty control unit. Therefore disconnect all control units one after the other and determine faulty control unit by the presence of a short.
  

Control unit faulty

Proceed as follows if the data link is OK and no fault was found by unplugging the fuses:

• Disconnect one after the other all control units which are connected to the diagnostic bus (see schematic). Repeat test step ”test diagnostic bus 01” after every disconnected control unit.
  If data transfer to the other control units is OK, the disconnected control unit will disturb data traffic. The control unit concerned should be replaced.