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Thread: Can Only Read 7E8

  1. #1
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    Can Only Read 7E8

    Hi guys, new to the forums so go easy on me. Basically just getting into this CANBUS business mainly to try and re-enable my clock on my Mazda.

    Heres the jist: I drive a 2010 Mazda Rx8, I recently changed my radio and after a battery disconnect, my clock dissapeared and the location of my temp reading moved to the other side. Now this isn't a big deal to most, but the issue is now the ambient temp doesn't read higher than 70F. I found that the information display resides on the canbus.

    The display still shows information for exmaple when i push my "mode" button on my AC controls. I was hoping to capture that so that I could find out what address that display resides on.

    I found this page http://www.madox.net/blog/projects/mazda-can-bus/ which shows some ID's.

    When i plug in the connector and turn on my software, I get constant readings from 7E8 (extended addressing is used i guess). If i try to change to 7E9 which on most cars is the tranny, the device resets the connection.

    Any idea what I can do here to get a dump of all addresses that exist on the bus????

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  3. #3
    Newbie preet's Avatar
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    It seems really weird that replacing your radio would mess with the info display like that. My car's default head unit connects to the SW canbus to get speed readings. Only thing I can think of was that your info display was somehow reliant on wiring that came out from your old HU? And... really strange that it shows ambient temp but now there's an upper limit.

    I don't think you can dump all of the addresses like you're trying to do. What device/software are you using? To find what you're looking for I think you need to monitor the data going through the bus. How to do that depends on your device/software combo.

    The last post in the comments section of the blog you linked to says:
    I’ve been having a play with the CAN BUS on the RX-8 and a lot seems to match.

    Anyway as you’ve been a great help I thought I’d give some back:

    0◊212 is abs, dsc off, traction control warning and brake warning
    0◊300 is steering warning light
    0◊420 is for temp and MIL/Oil warning/Coolant warning/Alternator warning (also oil pressure but while a ‘gauge’ it seems either on or off).

    0◊430 is coming *from* the instruments, don’t know what it is.

    I’ll give some more details when I have it nicely arranged but you might still be able to get something more from that.


    I'd try filtering messages from address 0x430... but I don't understand why you think it's related to your issue and what exactly you plan to do by figuring out which address and data represents your temperature / ambient temperature. Since you have a brand new car, why not just take it to the dealer and have them fix it?

  4. #4
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    Quote Originally Posted by preet View Post
    It seems really weird that replacing your radio would mess with the info display like that. My car's default head unit connects to the SW canbus to get speed readings. Only thing I can think of was that your info display was somehow reliant on wiring that came out from your old HU? And... really strange that it shows ambient temp but now there's an upper limit.

    I don't think you can dump all of the addresses like you're trying to do. What device/software are you using? To find what you're looking for I think you need to monitor the data going through the bus. How to do that depends on your device/software combo.

    The last post in the comments section of the blog you linked to says:
    Iíve been having a play with the CAN BUS on the RX-8 and a lot seems to match.

    Anyway as youíve been a great help I thought Iíd give some back:

    0◊212 is abs, dsc off, traction control warning and brake warning
    0◊300 is steering warning light
    0◊420 is for temp and MIL/Oil warning/Coolant warning/Alternator warning (also oil pressure but while a Ďgaugeí it seems either on or off).

    0◊430 is coming *from* the instruments, donít know what it is.

    Iíll give some more details when I have it nicely arranged but you might still be able to get something more from that.


    I'd try filtering messages from address 0x430... but I don't understand why you think it's related to your issue and what exactly you plan to do by figuring out which address and data represents your temperature / ambient temperature. Since you have a brand new car, why not just take it to the dealer and have them fix it?
    Thanks for the response. The OEM headunit had 2 harnesses, one that was radio power/speaker/etc and the other that was a smaller harness. This smaller harness is used across multiple things and is basically the can-bus. My AC controls have this smaller harness, and as you suspect, if I dont connect it, nothing displays in my panel . So there is no aftermarket unit that will display the clock and ambient temp. The older Rx8's had a metra connector, but that used a different interface and not CANBUS.

    I am using the ELMSCAN 5 and the software package that came with it.

    What I basically am hoping to do, is to see if there is a way to send a message to the display so that it "thinks" the radio is connected again so that it will display the clock. Wishful thinking? not sure.

    Here is what the display looked like before:


    Here is what the display looks like now:

  5. #5
    Newbie preet's Avatar
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    Hmmm. I looked at that diagram. I don't know what the effect of leaving that second harness unconnected is, but I'm assuming all it means is that connections 165 and 166 are no longer part of the bus.

    I'm not that knowledgeable with this stuff, and hopefully another forum member can give you better advice/ideas. Here's all I can think of:

    * I think you need to be on the MSCAN bus (pins 3 & 11 on the Mazda 3... double check for yours) and not the HSCAN (which the ELM will default to when searching). This bus is 125kbps. I don't know anything about the software that comes with ELMScan but you need to set it up to work with the lower speed MSCAN bus.

    * You said you can modify the display using the AC mode button. After establishing a connection to the MSCAN bus you need to set the ELMScan tool to be in monitor mode. This way it'll only listen to all the signals being broadcast on the bus.

    * What I'd do next is mess with the info display using that AC mode button and look for changes in messages that are on the bus. I'd try this with the car running on battery (engine off) to try and minimize bus traffic. The rest just comes from sifting through the data on the bus and looking for the address of the information display that way. Again I don't know how much the ELMScan software can help you with this.

    Let's assume you go through all this trouble and find that the information display address is 0x123. What then? To emulate whatever role the audio unit played you'd need to know the messages that were being sent back and forth between the information display and the audio unit. You don't know whether or not the information display directly requests clock data from the audio unit on demand or if the audio unit broadcasts the data at set intervals. You have to connect the original audio unit back in to determine this...Once you figure out how they interact, you'd need some standalone thing you can leave in your car that emulates the presence of the audio unit. Unless you have a carputer in there it seems like a lot of trouble =p. I hope I'm wrong though, and there's an easier way to do what you want...

    Preet
    Last edited by preet; 05-26-2011 at 03:45 AM.

  6. #6
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    Thanks for sticking with me through this, I really appreciate your attention. As far as the role of the radio, I think it might send some sort of "clock set" message to the bus. The hour/min buttons to set the clock are found on the radio. I am pretty sure that the radio doesn't continuously send messages, because when I swapped out my HU initially, the clock and the temperature were operating normally (As you can see in the first pic). It wasn't until I had to do a battery disconnect (for another project) that the display changed.

    My hope was to find the code to "set the clock", I guess it isn't as easy as i thought.

    As far as the elmscan5, you are right, I took a look at the hardware and it looks like it is only wired for the HS-CANBUS. I will try to remove the wire from the obd connector to the MS-CAN location (the same as you mentioned for the mazda 3) and then see if I can actually see some messages.

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