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Hey everyone.

I have been messing with my cars lately, specifically the canbus/linbus. I have a 2014 mazda 3 touring with tech package and a 2015 mazda 6 grand touring with tech and ieloop. I've been sniffing and playing with data on the different buses and compiled a short excel document with my findings. Figured I would share and others can add on to improve it.

So first of all what is CanBus?
It is a ControllerAreaNetwork Bus. Mainly used in automotive and industrial (elevators, factory machines, etc.) It runs two wires as a twisted pair that are inverse from each other to account for noise on the line as well as have a redundant link (ref to ground) in case one wire is shorted/damaged. (only implemented in some cases. Not sure on our cars if so).
Almost every system on the car is connected to the canbus, allowing every device in the car to communicate with each other. For example, the Start Stop Unit detects that the button on the door handle is pressed. It talks to TH LF unit over its own bus to authenticate the keyfob. Then it sends data to the Rear Body Control Unit to unlock the doors and turn on the interior lights. Or the PCM sends the engine's RPM to the Instrument cluster to display your on your tacho.

Since mommy and daddy ford made mazda, a lot of the comms are the same. Both have a High speed Can bus for critical components such as airbags, PCM, the instrument cluster, the ABS module, etc. Aside from that, we also have a Medium Speed Can Bus for less critical things such as the CMU, Blind spot monitoring, body control module, etc. Some components have their own CANBus such as the CMU which separates the vehicles MSCAN to its own that runs the Bluetooth module, cd player, etc.

Each device sends out data with a specific arbitration ID. The lower the value of the ID, the greater priority it has on the CANBus. A device can send more than one ID as well. The protocol of CAN may be standardized, but the messages are not. For example, a gen2 mazda can ID of 0x48 may show engine RPM while a gen3 mazda may show Transmission gear on ID 0x48.

There is also a linbus where the rain/light sensor is hooked into but that's a whole different thing that I was not interested in looking into. It is slightly different than canbus. It is more like IIC on one wire. The nodes usually are just listeners, whereas CAN can listen and send uniformly.



Anyway, hope you learned something from my basic overview. If anyone is interested in seeing what messages I have decoded so far, check out the attached excel doc. It has a few things on both busses. Some pages are blank because they shouldn't be public due to security/safety reasons or whatever.
 

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Cool stuff. I am hoping to gather communication from the FSC to the IC. Trying to troubleshoot HBC which is working but shows the amber warning light. I suspect the FSC is triggering the light but I don't know why.
 

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Wondering if too low or high a voltage is preventing me from reading my pcm? I bought this car not running and it has set for over a year with the pcm removed transmission in the trunk and a bad motor. It’s a 2010 2.0 manual transmission. Both my high and low can are out of spec for min and max voltage and I can’t connect to my car. I also have a rapid security system flash on the dash. I have a MAC handheld scanner and a Autel scanner capable of reprogramming my security. When I attempt to start the car all light on dash come on, engage clutch and fuel pump comes in but no start? Any help !!?
 
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