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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.

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  • Worth searching on here, lots of questions about OBD and data...
    – Solar Mike
    Jun 17, 2019 at 10:39
  • I searched. But I didn't find a similar question. But sometimes users (like me) just don't know the best words for a search...
    – Edgar
    Jun 17, 2019 at 10:44
  • Obd or obdII or obd2 is one search, can bus or canbus is another, several questions on here as I have read a few and commented on a few as well...
    – Solar Mike
    Jun 17, 2019 at 11:02
  • @SolarMike: I searched for user:10976 in combination with OBD and CAN-BUS and I did several other searches and I did not find any question or answer similar to my question. I understand the concept to do some research before asking a question. I did that. But I don't plan to read hundreds of questions with just the word OBD because most of them are certainly not related to my problem. If you think you or someone else answered my question already then please mark it as a duplicate and include the link to the answer. Thanks.
    – Edgar
    Jun 17, 2019 at 11:14
  • But a quick search gave : mechanics.stackexchange.com/a/32096/10976
    – Solar Mike
    Jun 17, 2019 at 11:16

3 Answers 3

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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

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  • The sensor is there. It's a NTC which is connected to the engine control unit. I can see the air intake temperature in the OBD log files and in the CAN frames which are for OBD (7E8). But until now I don't see them in the broadcast CAN traffic (20,000 frames per minute). I will search a little more.
    – Edgar
    Jun 18, 2019 at 6:29
  • Does it have a MAF?
    – somebody
    Jun 18, 2019 at 7:07
  • As I recall (when a MAF is involved). The air is heated, and the calculations are done on the wire. The computer calculates the temperature based on the air flow, and the voltage to the heater, after "sniffing" the exhaust.
    – somebody
    Jun 18, 2019 at 7:14
  • In this case the temperature sensor is in the air filter box.
    – Edgar
    Jun 18, 2019 at 8:17
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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.

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  • On my bike it broadcasts about 20,000 CAN frames per minute. I can see data from brake pressure, engine data including water temp, RPM, gear, etc. Some of that data like i.e. RPM is also available in ODB but other data like gear, brake pressure, and many other is not available on OBD. I just started to analyze the raw data and it will take some time to find all the details. It's a very modern bike...
    – Edgar
    Jun 18, 2019 at 6:25
  • Another good example if the front light. The LED front light has no wires or connection for low beam, high beam, etc. It has power connector and CAN-BUS connector. I found already the CAN broadcast frames for low and high beam. They are available in the broadcast traffic but they are not available (as far as I know) in OBD.
    – Edgar
    Jun 18, 2019 at 6:32
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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.

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