turbogrill Posted January 30, 2022 Report Share Posted January 30, 2022 Hi, Can I send custom CAN messages on the OEM Mazda CANBUS without confusing the ECU? I currently have 2 CAN buses, the OEM Mazda Bus and the race capture pro canbus. I would like to only have 1 but then the Mazda ECU would see messages it doesn't recognize. Could that be a problem? Would a OEM ECU freakout if there was unknown messages being sent? Quote Link to comment Share on other sites More sharing options...
Robmink Posted January 31, 2022 Report Share Posted January 31, 2022 I doubt it. Most control modules on the bus have built in filters that disregard unneeded messages. Otherwise the inbox would quickly fill with a bunch of (for want of a better word) spam. I know for a fact that it does not matter to VW ECMs, or to the AEM replacement I use now. Just make sure that the message IDs don't match any IDs that are currently being used, and more importantly, were being used in a stock car. Also, stay out of the 0x7XX range since that tends to be diagnostic messages to and from a tester, and make sure that the priority of your new messages isn't so high that crowds out the ECM. In general, lower message IDs have a higher priority. 1 Quote Link to comment Share on other sites More sharing options...
turbogrill Posted January 31, 2022 Author Report Share Posted January 31, 2022 38 minutes ago, Robmink said: I doubt it. Most control modules on the bus have built in filters that disregard unneeded messages. Otherwise the inbox would quickly fill with a bunch of (for want of a better word) spam. I know for a fact that it does not matter to VW ECMs, or to the AEM replacement I use now. Just make sure that the message IDs don't match any IDs that are currently being used, and more importantly, were being used in a stock car. Also, stay out of the 0x7XX range since that tends to be diagnostic messages to and from a tester, and make sure that the priority of your new messages isn't so high that crowds out the ECM. In general, lower message IDs have a higher priority. thanks! Quote Link to comment Share on other sites More sharing options...
Scott Posted February 4, 2022 Report Share Posted February 4, 2022 Matches my understanding. A device on CAN will have a list of messages is listening for and ignore others. Again, don't use a source address anyone else is using. Quote Link to comment Share on other sites More sharing options...
Grant Posted February 7, 2022 Report Share Posted February 7, 2022 No problem all; I've done this quite a bit. Try to use unique ids and change them if something is acting weird. Also remember that lower id messages get priority over higher id ones. We do use two separate CAN buses though. This is how OEMs do it, so a failure of a non-essential bus doesn't brick the car. 2 1 Quote Link to comment Share on other sites More sharing options...
Robmink Posted February 9, 2022 Report Share Posted February 9, 2022 On 2/7/2022 at 4:46 AM, Grant said: We do use two separate CAN buses though. This is how OEMs do it, so a failure of a non-essential bus doesn't brick the car. We also use separate buses because there is only so much headroom on any bus and some messages must get through, like the ones between the trans and the engine, and the engine and the ABS. Since those tend to run at a high rate, they crowd up the bus pretty quickly. Quote Link to comment Share on other sites More sharing options...
turbogrill Posted February 9, 2022 Author Report Share Posted February 9, 2022 (edited) I will keep two buses, should be easy enough. My original plan was to connect a CAN based microcontroller for various stuff but that only had 1 channel. The NC Miata baud rate is 500kbs I believe, the ECU transmits various CAN packets for the instrument cluster and supposedly the ABS module sends out wheel speed sensor data quite often. (I think this is for the instrument cluster to get speed). Not sure if the ECU or ABS needs any CAN packets. The ABS module has it's own brake sensor. Edited February 9, 2022 by turbogrill Quote Link to comment Share on other sites More sharing options...
Robmink Posted February 10, 2022 Report Share Posted February 10, 2022 21 hours ago, turbogrill said: I will keep two buses, should be easy enough. My original plan was to connect a CAN based microcontroller for various stuff but that only had 1 channel. The NC Miata baud rate is 500kbs I believe, the ECU transmits various CAN packets for the instrument cluster and supposedly the ABS module sends out wheel speed sensor data quite often. (I think this is for the instrument cluster to get speed). Not sure if the ECU or ABS needs any CAN packets. The ABS module has it's own brake sensor. Some of the Microchip dsPICs have 2 channels, as does the ARM STM32F3 & 4. I use the STM32F4 as my dash display unit and to act as a kinda gateway between the VW based bus stuff and the AEM/AIM hardware. The VW ABS transmits both individual wheel speeds and a combined speed that is used by both the ECM and the dash. I doubt the Mazda ECM needs anything from the other modules in order to run, but saying that, I know some VW ECMs do not like it if the ABS is offline (it's a safety thing). Usually, just sending blank messages with the correct address is enough to satisfy the module, you'll just get a bunch of faults for missing data. I'm a bit of a CAN bus nerd. 2 Quote Link to comment Share on other sites More sharing options...
turbogrill Posted February 10, 2022 Author Report Share Posted February 10, 2022 28 minutes ago, Robmink said: I'm a bit of a CAN bus nerd. I will keep you on speed dial. 1 Quote Link to comment Share on other sites More sharing options...
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