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TCAN4550: Communication problems with OBD port from Honda vehicles

Vincent Kwok
Prodigy 240 points
Part Number: TCAN4550

Tool/software:

Hello Interface team, I have a customer with an issue regarding TCAN4550. I will include them in the thread.

They are trying to communicate to a car via OBD II ports. They are using the TCAN4550 and it is working well in most cases.I will paste a segment of their email:

"Our current design uses TI's TCAN4550 transceiver.  In general, OBD communication works as expected: our firmware can read PIDs successfully from the OBD ports of many test vehicles that we tried.  However, we seem to run into issues with vehicles from the Honda brand, meaning both Honda and Acura cars.  Firmware sends the OBD request at the standard OBD CAN ID, but never receives any response from the expected CAN IDs.  Using a CAN analyzer, I can see a lot of CAN traffic, but none of them are OBD messages.  A commercial OBD reader seems to work fine, it doesn't like the car has a problem.

 

I doubt it is a TCAN issue, but I just wonder if you know of any problems with using TCAN to communicate with OBD port from the Honda brand?"

Thanks!

  • 0
    TI__Prodigy 240 points

    Hello Interface team, any updates on this?

  • 0
    TI__Guru 53555 points

    Hi Vincent,

    I'm not too familiar with the higher level OBD protocol used by different manufacturers. From the perspective of the CAN protocol the TCAN4550 should be able to interpret any CAN or CAN FD message that appears on the CAN pins as long as it is configured for the same data rate (both nominal and data) that is used by the car. From a hardware perspective I would recommend ensuring that the OBD reader is not overloading the bus. The CAN bus expects two nodes with 120-ohm termination for an equivalent total 60-ohm load. Some OBD ports may expect the reader to supply one of these terminations. Others may be fully terminated without the OBD, so adding an additional 120-ohm would overload the bus (40-ohms between CANH and CANL). If this is the case then the termination resistor should be removed from the OBD reader. This can be checked using a multimeter on the CAN bus pins of the OBD connector while the system is off. A reading of 120-ohms would require the OBD to supply termination, a reading of 60-ohms would require the OBD to be unterminated. 

    Let me know if any of this helps or if there is other information I can help provide to bugfix this issue. 

    Regards, 
    Eric Schott