CAN Network Diagnostics

Are you having difficulty diagnosing communication problems on a vehicle?

A Snap-on® platform can help you to overcome the challenges and get to the root cause of the problem.

You will need to use the lab scope function, because that’s the only way to test a vehicle’s CAN network, but once you’re hooked up your tool will tell you what you need to know.

Using a Snap-on VERUS® Edge car diagnostic tool as an example, connect to a DLC break-out box using channels 6 and 14, which will be the same whatever you are working on as all CAN network vehicles terminate on pins 6 and 14 as standard. Connect the ground to pin 4 or 5.

Set both channels on your lab scope to a 10v scale to give yourself a large, clear window in which to analyse the data, then set the time base down to 100 micro-seconds.

Pause the scope to take some measurements. The squares shown on the graph illustrate when data is being transferred within the vehicle but your main interest will be in the voltages being recorded.

Where the yellow and green lines meet you want to see a reading of around 2.5v then when the lines separate, during data transmission, one should go up by a volt and one should drop by a volt if everything is operating correctly.

Setting the channels to a 10v scale has the added advantage of making it easier to see when there is an issue – if one of the lines drops to zero then there’s a bad ground or ground issue, while if the voltage rises outside of the expected readings then there is a power problem.

So as you can see, the lab scope option is a straightforward way to help diagnose communication on CAN network vehicles and should always be considered.

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