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Discussion and questions related to the course CAN Bus Communications Decoded
Could a aftermarket Dash be configured to display information from the OE Diagnostic can bus . Like SCT or HPTuners scanner software is able to display perimeters ???
Many can. AIM & Motec are a couple I'm familiar with. But be aware, for a device to display data from the OBD2 system it has to request each single piece of data from the ECU, so it is generally is very slow. Even with just a couple of channels there will be noticeable lag from real-time and the more channels you want the slower it gets. Data is not just constantly broadcast out of an OBD2 port at a high rate like is normally used for displays. There are some manufacturer specific high speed modes which are probably what SCT etc uses rather than the generic OBD2 modes.
to expand on the topic. UDS is a communication that is best explained as 'dynamic and structured' I've yet to find a dash capable of logging information such as manufacturer specific PIDS. most, if they are not a multi message response, need about 3 multiplexers to manage appropriately using 'extended multiplexing' scenarios.
as of yet I haven't found any dash capable of
To expand further/help me in my scenario...apologies if this is getting into the weeds a bit..
Motorcycle built n 2007, so has a OBD2/K-line diagnostic connector, and the only CANbus is between the ECU and dash, no other nodes. I have tapped into the Canbus and reverse engineered the messaging to get most of the data I need to my Aim datalogger. However, this particular OEM dash does not have a fuel gauge, only a low fuel light (I have found this message and created the alarm in the Aim dash).
From my OBD2 scanner/software there is definately a voltage signal representing the fuel level so I know the data is there somewhere. My assumption is the fuel level signal is still getting transmitted to the dash via CAN, which then activates the low fuel caution through internal circuitry. I could be wrong though obviously, as it's possible the ECU computes the logic for 'fuel signal below/above x volts' and subsequently just transmits a single bit on the CANbus for the dash to activate its light. Yet to determine this.
So by sending a PID request at only 1Hz via the datalogger, then listening out for the response on the same logger..should/can this work?
My understanding from Aim is that transmitting a 0x7E0 (with byte2 containing 0x2F for fuel level %), then listening for the response at byte 3 of a 0x7E8 message, the ECU should be responding to the PID with the information requested should it not? Or am I completely misinformed/misunderstanding..the grey areas which I suspect will prevent this from working are:
a) not all ECU's respond to all PID msgs even if they are meant to as per SAE standards
b) limitation of my datalogger CAN output line
Thanks in advance to anyone committed enough to reading this and attempting to educate!