Unchecking Listen-Only Mode

[gearsh]

Hi there. First time posting here.

I'm currently doing a project wherein we try to sniff Telemetry data on trucks using the PCAN-USB tool and PCAN View application installed on a PC.
On the European trucks (ie Scania, Mercedes), we are able to sniff full CAN data at 250 kbit/s which is the FMS standard (derived from J1939 standard). On some select models, I've noticed that we are only able to get a single stream of data (ie tachograph) when checking Listen-only mode but we are able to get full CAN data when unchecking Listen-only mode. I'm not trying to transmitting any messages, but only aim to receive.

So comes my question: Does the sniffer send out any message to trigger the CAN interface of the truck to be able to give full CAN data? If so, what message is this?

I appreciate your help in this.

Regards

[PEAK-Support]

When you run our Devices in listen only mode - no other node could see that this device is on the Network. It does not work as active node and so also do not ACK any send CAN Frames on the Bus.
If the ECU work as a Gateway maybe it could see if there is a 2nd active node on the Bus and then send out more information - but we do not know exactly how the system is setup.
Best is to contact the manufacturer of the vehicle to get more information.

[gearsh]

Thanks for your reply. We'll reach out to the manufacturer as well.

I just wanted to understand if the normal mode (unchecked listen-only mode), when initially connected via PCAN-view, sends any CAN frames on the bus?

Also, when you say the PCAN USB is an "active node" what does it do?

[M.Maidhof]

Hi,

in "active mode" it will not transmit any frames (as long as you have no active frames in the transmit list of PCAN-View), but it will acknowledge the frames on the CAN, or will set the error flag, when there are broken frames.

https://en.wikipedia.org/wiki/CAN_bus#ACK_slot

regards

Michael

[gearsh]

Thanks. In my set up, I'm not transmitting any CAN messages and just sniffing from the truck interface.

Kindly confirm if my understanding is correct:
On normal mode (unchecked Listen-only), the PCAN USB acknowledges that it has received a valid CAN frame. The truck CAN network (or ECU) receives the ACK and seeing that there is an active node, starts sending the full CAN data - I'll check and dig for more information from the truck manufacturer/s.

Regards

[M.Maidhof]

Hi,

yes, your understanding is correct.

regards

Michael

[gearsh]

Thanks, Michael.

From the manufacturer documentation, and from our testing, their CAN interface is coming off from an FMS module/ FMS interface. Some make and models give out the full CAN data even when sniffing on "Listen-only mode" while other models only do so when unchecking Listen-only mode.
I suppose this same setup is what U.Wilhelm meant by ECU acting as a gateway. Would you be able to point me to where I could get sample diagrams of how the CAN network is set up or where the ECU works as a "Gateway".

Regards,

[PEAK-Support]

sorry - we do not have/offer such sample diagrams. You need to connect the manufacturer of the FMS Interface/Gatewy to get more info how to get the Data from the BUS/how to set the Gateway to a mode where it sends the FMS data.
As i wrote some nodes need a 2nd active node, others don´t - but this is a question you need to ask the ECU manufacturer - we do not have this info - we sell CAN PC Interfaces.