Are all OBD current data available on the CAN-BUS without request?

Question

I am analyzing the CAN-BUS data from my motorcycle.

I logged all the CAN-BUS traffic. One time with an ELM327 adapter connected and one time without.

I am searching for the value of the Intake air temperature. When the ELM327 is connected I see the OBD 7DF Request and 7E8 Response messages. Request: 02010F0000000000, Response: 03410F4E00000000 = 38 degrees Celsius

But I can't find this value, or something related, anywhere in the CAN-BUS traffic in the "normal" CAN-BUS traffic, not the OBD response data.

For other values like RPM I can see them in OBD messages like 04410C21A0000000 = 2152RPM and the same value for CAN-ID 540 and messages like "02 08 68 .. .."

My question is: Should all values which can be requested by OBD be part of the normal CAN-BUS traffic, also if no OBD requests happen? Or is it possible that I have to request that value if I want to see it on the CAN-BUS.

I searched and I am pretty sure the Intake air temperature is not part of the CAN traffic. But there is still data which I didn't fully analyze until now. I ask here so that I don't waste my time looking for something which maybe does not exist.

I know that data in the CAN-Frames can be in one or more bytes and there might be calculations involved. I figured out lots of other values in the CAN traffic so in principle I know how this works.

Edit: Currently my work is on a KTM Duke 390 (2017) which uses modern electronic like throttle by wire. It has a diagnostic connector with the CAN-BUS output 500kbps. I didn't mention this in the original post because my question should be independent from any vehicle. Likely later I will work on another bike and maybe the same question comes up.

Edit2: To clarify what I have in mind: I want to build a device which listens to the CAN bus and analyzes the data. One part is that I want to build an extra brake light which is more powerful if I brake harder. I can do that now because I found the brake pressure in the CAN bus data which provides a 16bit value of the front brake pressure. I have something else in mind for which I need the intake air temperature. Currently I could already request that data OBD style and use the OBD response message. But if possible I only want to listen on that CAN bus. So if I can find that value without requesting it (per OBD message) that would be better. I could also measure the voltage on the wires from the NTC (resistor which changes with the temperature) and use an analogue digital converter. But why should I do that if that value is measured already and available on the CAN bus. That's the idea.

Answer 1

I would have probably posted this in the comments. But don't yet have the "creds" for commenting in this forum. That said; you can easily determine whether there might be data for the information you seek, by finding a/it's related sensor for that data.

But intake is almost always only air flow.

HTH

Answer 2

On a lot of platforms constant broadcast messages are blocked by the CAN gateway. The only way to determine if it’s broadcast without request is to CAN log after the gateway. I wouldn’t be surprised on this platform nothing is broadcast.

Answer 3

To answer my own question: I am 99% sure that some data which is available by OBD request is not broadcast on the CAN bus without request.

I analyzed a lot of data from my bike and the intake air temperature is not broadcast.

I guess the reason is that only the engine "cares" about this information. There is no point to broadcast it to "everyone". Info like brake pressure or wheel speed is broadcast - I guess because it is used by several components in the vehicle.

To be sure that there is no misunderstanding: I don't know which parameters are broadcasted in different vehicles and which not. My question was if maybe some parameters are only available on request (independent of the vehicle) and I confirm this is the case. Some parameters must be requested, otherwise they are not available on the CAN bus.