ELM327 OBD2 pins requirements?

Discussion in 'Gen 3 Prius Technical Discussion' started by deis, Jan 15, 2021.

  1. deis

    deis New Member

    Joined:
    Dec 10, 2020
    6
    0
    0
    Location:
    UK
    Vehicle:
    2011 Prius
    Model:
    Excel
    Hi all,

    So to make sure I get all my PID's being read by Torque Pro I'm building my own ELM327 module based on the ELM327 v2.3 which is on it's way from Canada as we speak. I just want to double check with someone if my pinouts are correct for it to work?

    I'll have pin 4 and 5 to GND, 6 CAN H, 14 CAN L and 16 +12V. So basically, just 5 pins (two grounds). So those pins are a given. Am I safe to miss out the ISO-9141-2 protocol and the J1850 protocol for the ELM327 circuit? It won't be used for communicating with anything else will it?

    For the curious, the circuit I'm basing it on is found on page 84 of the official data sheet. The part of the circuit I'm not doing is underneath the ELM chip, pins 2 and 10 (J1850), and the part under the CAN circuit for pins 15 and 7 (ISO K and L respectively). I'm using a Microchip BM71 Bluetooth module and the recommended ADuM1201 logic level translator between them.

    I'm doing all in SMD stuff too, I like a challenge!

    I could have used the ELM329, but I don't know if Torque Pro would work the same. I haven't really looked into the technical differences as much. I might actually build a dedicated CAN one for my car and implement the low voltage stuff for the ELM329 and do the complete one for the ELM327. If I get this working, I might make a few more and sell them before ELM Electronics close down in 2022.

    Any feedback would be appreciated. Thanks
     
  2. Elektroingenieur

    Elektroingenieur Senior Member

    Joined:
    Jan 8, 2017
    1,995
    2,692
    9
    Location:
    California
    Vehicle:
    2016 Prius
    Model:
    Three Touring
    The Repair Manual and Electrical Wiring Diagram (more info) for third-generation Prius cars sold in Europe show that terminals 2 and 10 of the Data Link Connector 3 (DLC3, Toyota’s name for the connector that also implements the required OBD II capabilities) aren’t connected, so you won’t need support for SAE J1850.

    Besides the five terminals you mentioned, terminal 7 is connected to the tire pressure warning ECU, telephone transceiver assembly, and headlight leveling ECU assembly (if equipped). The Repair Manual describes this only as the “Bus ‘+’ line,” but I think it’s the “K” line of one-wire ISO 9141-2. I don’t know if the Torque Pro software even uses this, or what you’d miss by not having it.
     
  3. deis

    deis New Member

    Joined:
    Dec 10, 2020
    6
    0
    0
    Location:
    UK
    Vehicle:
    2011 Prius
    Model:
    Excel
    I think the Torque Pro would use whatever protocol it find complete first, which would be the CAN in our case, I don't know if it would use the ISO9141-2 as well for reading extra PIDs.

    It must be a Toyota thing for when they connect their expensive computer to the car to update the other buses, I think they have a LIN bus for the av/telematic stuff?
     
  4. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    11,194
    8,141
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    The "multiplex communication" section of the New Car Features manual shows all the car's different networks and their interconnections, a glory to behold.
     
  5. mr_guy_mann

    mr_guy_mann Member

    Joined:
    Sep 3, 2020
    432
    186
    0
    Location:
    NJ-USA
    Vehicle:
    2006 Prius
    Model:
    Four
    I guess the only thing you might want to investigate is whether the chipset you are going to use can properly "address" the modules on the bus. That seemed to be the big factor on the Dr Prius site as to which adapters would or wouldn't function with that app.

    Posted via the PriusChat mobile app.
     
  6. deis

    deis New Member

    Joined:
    Dec 10, 2020
    6
    0
    0
    Location:
    UK
    Vehicle:
    2011 Prius
    Model:
    Excel
    From what I understand, there are a lot of Chinese clones of the "original" ELM327 chipset because they initial version of the firmware was easily copied, but the later versions had copy protection features on them. The initial and copied version was 1.0 or 1.1. The clones are marketed at version 1.5, but now ELM Electronics have a version 2.3 of firmware written to the chipset. Mine arrived the other day from Canada. I'm literally laying out the board on Eagle as we speak. The chipset speak to ISO L and ISO K, J1850+ and CAN.
     
Loading...