CAN strange shape on scope

[Chriss]

Hi!
I'm trying to connect a car ecu on my bench to my diagnostic tool but no way to do that.
I have experience in that cos I use ecu's many times on my bench.

When I checked the Can-H and Can-L with my scope I got a strange signal. Look the at the picture.

I'm not sure what should I look for.
Any idea where to start to troubleshoot?

Thanks for any advice.

[jwet]

Its a differential signal.  Use your scope math function if it has it to subtract the two, it will make more sense.  Otherwise go through a CAN physical interface chip to get get a single ended signal.  It does look funny though.  Pay some attention to grounding and don't have other equipment connected. (see Dave's video on how to blow up your scope)

[Chriss]

Thanks for your time spent to replay.
The CAN-H and CAN-L signal is in a kind of infinity loop. Like if you would pulse two signals with an NE555.
I never saw that kind of "looping" CAN signal.

[jwet]

Me neither- Learned something.

[Chriss]

Problem solved a couple of minutes ago.
The CAN line is not terminated in the ecu.
When I put a 120R across the CAN lines the
signal shape is now perfect.