Diagnosis on the local interconnect network bus

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Definition:

The local interconnect network bus (LIN bus) is a serial, single-wire bus, standardized for the automotive industry (a single-wire bus has only one line). The data transfer rate of the local interconnect network bus ranges from 9.6 kBit/s to 20.0 kBit/s.

Possible faults causes for the local interconnect network bus:

Incorrect voltage supply or faulty ground connection for the affected components on the local interconnect network bus
Faulty slave on the local interconnect network bus
Faulty master control unit
Short circuit to B+ or GND on the LIN bus line
Line disconnection or faulty plug connection

Carry out a function check on the affected local interconnect network bus before starting troubleshooting.

In line with the wiring diagram, carry out a function check between the bus users on the local interconnect network bus:

Conduct a status request
Activate the button

If the status request or the activation is successful, it may be assumed that there are no problems with the communication on the local interconnect network bus. If this is the case, no further troubleshooting on the affected local interconnect network bus is required .

Troubleshooting in the event of faulty communication on the local interconnect network bus (function check is faulty):

Check voltage supply and ground
In line with the wiring diagram, check the voltage supply and ground connection of the affected components on the local interconnect network bus (master and slave).
Carry out an oscilloscope measurement according to the wiring diagram. Check (master control unit).

NOTE: A faulty slave cannot be found by the oscilloscope measurement.

Example of an oscilloscope measurement in an intact system or with a faulty slave on the local interconnect network bus. Measurement of the LIN bus line to ground (faulty slave on the local interconnect network bus).

Fig 1: Display - Oscilloscope Measurement Screen

Courtesy of BMW OF NORTH AMERICA, INC.

NOTE: The voltage levels of the communication on the local interconnect network bus are nevertheless steady.
Depending on the number of participating slaves, the load on the local interconnect network bus increases accordingly.
In this case, it may be assumed that there is a faulty slave on the local interconnect network bus .

Example of an oscilloscope measurement with no master control unit communication. Measurement of the LIN bus line to ground. (faulty master control unit on the local interconnect network bus).

Fig 2: Display - Oscilloscope Measurement Screen

Courtesy of BMW OF NORTH AMERICA, INC.

NOTE: In the event of a faulty master control unit, a constant dominant signal can be seen on the local interconnect network bus.
In this case, it may be assumed that there is a faulty master control unit .

Perform a line check according to the wiring diagram:
- Check of the affected LIN bus line for short circuit to B+ and GND
- Check of the affected LIN bus line for interrupt
- Check of the affected plug connections

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