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Thread: Controller Area Network (CAN) Bus Communication Faults

  1. #1
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    Default Controller Area Network (CAN) Bus Communication Faults

    Hello everyone....

    Last time I send my car to my Chevrolet agency due to a drawing message "a drawing of car with a mechanical key" ...during revision I saw over the hand-held terminal (DTC) in the shop , "50 messages", ... mostly regards to CAN Bus communication problems, on which the service manager told me thay these messages are not true messages. They were told by one of the representatives of Opel in Mexico, that these messages come up but should be dismmissed, I mean not take care of them....

    in specific... some of the messages said: for example (translated from spanish to english)

    a) #U2103 "failure over the chassis module controller BCM. Intermitent failure.
    b) #U2117 " in BCM module, , No communication from Bus CAN to DIS.
    c) #B3717 "no Bus CAN communication to UEC.
    d) #2116 "No BUS CAN communication to IPC (instruments block).
    e) #U2113 No BUS CAN communication to SDM (airbag diagnostics and detection system....
    f) ...etc. etc. etc. etc. etc.

    well...just to mention some of the messages..............


    ofcouse I don´t agree, and I still talking with them and get them fix it.

    Can someone get me some advise on this please? what might be happening?


    I know CAN protocol is a very old, but trusting communication,...born in Germany kind of serial comm, but I think that there might be something wrong in one of the modules, ... there is too many messages related to CAN Bus communication problems,

    or does this regular happen to a new VEctra-C ????

    regards, thanks..

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    Regular Member Green Growler's Avatar
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    Personally, I wouldn't worry about the messages or the quantity of them, on recent trip to a dealer I think I made about 35-40 "error" messages.
    I would concentrate on any symptoms, if you have any, and get the dealer to sort the faults, not worry about "error" codes.
    One quick question, have you changed, or come to that, remove the head unit for example ???
    The headunit is seen by the canbus system as a module, and if it is not there, this causes a number of "error" messages.

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    Quote Originally Posted by Green Growler
    Personally, I wouldn't worry about the messages or the quantity of them, on recent trip to a dealer I think I made about 35-40 "error" messages.
    I would concentrate on any symptoms, if you have any, and get the dealer to sort the faults, not worry about "error" codes.
    One quick question, have you changed, or come to that, remove the head unit for example ???
    The headunit is seen by the canbus system as a module, and if it is not there, this causes a number of "error" messages.
    Hi Green, thanks for your reply....

    regards the messages, I do worry because mostly are related to Communication problems, infact studyng about the CAN protocol, you can see that if there is any module on the network that is interminent having problems (communicating) this leads to break all the CAN bus communication,... then you may get lots of errors from almost all of the modules that were or were trying to communicate at that moment.
    So there might be a module that is not working properlly all times, and yet is difficult for my dealer to detect this kind of errors since they are not present always.....

    about simptoms, well, I got problems with driver door control module one time, then I have posted also the cilinders problems small vibration on the mornings,

    About the head unit, where is it?..... are you saying that I should remove the head unit to make a comm test or something like that?,

    I think it could be any module, when a module is not present you might get an error. right?

    thanks Green,

    regards,

    SC

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    One of the key points of the Canbus system, not that I'm an expert, far from it, is that communication errors are not critical.
    If a communication error occurred in a critical system using canbus (I'm not saying all these systems do, but for example) like engine management, ABS, traction control, then that could have pretty catastrophic consequences. Therefore the system is designed to accept that from time to time there will be comms errors, I guess it is seen as somewhat inevitable in such a harsh environment as a motor vehicle. As such, these module are all inter linked in such a way to create a VERY stable system, meaning nothing bad should happen if a comms error occurs or a module crashed or something.

    When I say headunit, I mean the radio, or stereo, whatever you want to call it.
    It is something many people change for a far better after market one, or indeed remove it to gain access to something else.
    The canbus system sees the headunit as a module, and simply changing it will cause "errors" but these are expected and cause no harm.

    Like I say, it is just my opinion to concentrate on any systems of what, if anything, appears to be wrong with the car, rather than worry about "errors" which are most likely nothing at all to worry about.

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    A canbus system is designed to cut down on all these wires running around the car and improve the way in things are reported.

    The actual canbus system is extremely simple being 2 wires with 120ohm resistor at both ends. All the modules then feed off the CAN bus. They do not sit in series within the CAN bus.

    I can explain in more detail if you wish but it isn't a issue your errors.

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    CDTi, how does the whole fault code system work on a CAN bussed (?) vehicle? Suppose that a code Annnn is showing, which module is reponsible for triggering that code? Is this even a sensible question to ask?

    Ta.

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    Quote Originally Posted by CDTi
    A canbus system is designed to cut down on all these wires running around the car and improve the way in things are reported.

    The actual canbus system is extremely simple being 2 wires with 120ohm resistor at both ends. All the modules then feed off the CAN bus. They do not sit in series within the CAN bus.
    Am I right in thinking that pre 2005 cars have a partial Canbus system and cars after 2005 have a full Canbus?

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    Haven't seen the pre 2005 cars Alex, but I have a suspision as they have different radios and steering wheels.

    Mine defo is a full CAN bus system.

    The CAN bus is just a high speed serial link around the car. Modules come off it. The CAN bus is just used for communication between the modules. The ECU will be the main module still, with all the additional modules reporting to the ECU.

    For example the ABS module with discover an error with the sensor but won't actually do anything. All it will do is send this signal down the canbus to the ECU. The ECU then decides if this should do something (Flash a light or go into safe mode) or just record this as a non-critical error. This non-critical error is logged as an error which you get as described earlier.

    Normally there are around 3 types of error codes:

    Alarm - Car logs the fault but continues to run without any effect in performance. For example if you have the Vx radio unplugged, this will flag the error, but it is not determental to the cars performance and general running. But still an error.

    Fault - For example an ABS error, it will display a light and disable that module as it is not functioning incorrectly. BUT this doesn't affect the cars engine performance and general running.

    Serious Fault - Cam or crank sensor failure for instance. The car cannot accurately run the car without knowing the exact cam and crank speeds. So for safety puts the car into limp home mode and puts all parameters within the ECU to safe settings.

    It is quite hard to explain! I can draw a diagram if needed?

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    A very quick diagram as I am at work but it shows you the rough idea behind it. The cabbus is a shielded cable to avoid interference.

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    Thanks CDTi. I understand the idea of having high speed serial buses running all over the place. I'm actually trying to work out how to determine what might be wrong with my car and what modules can report error codes. (Perhaps not specificaly CAN related...) eg. As I understand it, Unnnn codes are related to CAN network failures - but what module(s) is/are responsible for determining/reporting this?

    Quote Originally Posted by CDTi
    Haven't seen the pre 2005 cars Alex, but I have a suspision as they have different radios and steering wheels.
    I recall reading somewhere that the newer Vectra C display (DIS?) modules don't have an analog interface to the radio, only CAN. On the other hand, I suspect the steering wheels are logically the same, just laid out differently. But I could be wrong...

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