Local Interconnect Network - LIN bus - voltage

The purpose of this test is to investigate the presence of LIN-BUS signals and circuit integrity in relation to systems connected.

How to perform the test

View connection guidance notes.

1. Use manufacturer's data to identify the LIN-BUS circuit and connected components.
2. Connect PicoScope Channel A into the LIN-BUS circuit and to a good earth.
3. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
4. Start the scope to see live data.
5. Operate the systems connected by the LIN-BUS to observe signal changes. Move connectors and wiring loom fixings to look for any signal drop-out.
6. With your waveform on screen stop the scope.
7. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Note:

 LIN-BUS circuit access can be gained at individually controlled components.

Example waveform

Waveform notes

As you can see from the example waveform, the LIN bus waveform is a square wave, representing the binary states in a serial data stream. The waveform observed should be free of obvious distortion and noise spikes, and the upper and lower levels should be approximately as in the example (for a 12 V system).

The lower level voltage (logic zero) should be less than 20% of battery voltage (typically 1 V) and the upper level voltage (logic one) should be more than 80% of battery voltage. Note that the voltage levels may change slightly when the engine is started.

We cannot decode the data stream using a scope, so the purpose of this test is to verify that the signal is both present and correct, and is not interrupted by moving the wiring harness or gently tugging the connectors. Faults may be specific to a particular function, such as a non-operating window, or general, where all the functions on the bus are not working. Before condemning a device, use the scope to check that it has power, ground, and a present and correct LIN signal.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, Lin bus

Further guidance

Local Interconnect Network (LIN) bus communication is becoming more common on modern CAN Bus-equipped vehicles. It is essentially a low-speed, single-wire serial data bus (a sub-bus of the faster, more complex CAN Bus) used to control low-speed non-safety-critical housekeeping functions on the vehicle, especially windows, mirrors, locks, HVAC units, and electric seats.

The LIN bus is proving popular because of its low cost and also because it reduces the bus load of the supervising CAN network.

AT124-2