ISO9141 Interfaces

User topics relating to hardware that interfaces PCs to ECUs

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ISO9141 Interfaces

Postby Evo4Mad » Tue Jun 14, 2005 12:10 am

1st you need an electronic interface between the PC serial port and the OBDII connector under the steering wheel dash, a straight through wire cable will never work, because the OBDII ISO9141-2 is 0v(0bit) ->12v(1bit) whereas the pc serial port is -25v(0bit)->+25v(1bit)

Some hardware interfaces that will do the OBDII->PC Serial Port voltage conversion:
Direct ISO Packet Senders:
1) (sells a circuit board and components) (I have a schematic for this board if you want it)

2) (only provides schematics)

Smart ISO Data Packet Device:
ELM323: ... m#packages
(hardware has a timing chip and handles baud rate and data packet crcs etc.) You can buy the elm323 chip and the empty circuit board on their own.

OBDII plug pins:
pins4&5 are -ve (ground)
pin16 is 12v (used for power for circuit board for the ECU side of the circuit)
pin 7 is the K-Line (used for MUT to send and receive data from the cars computer)
pin 1 must be joined to pin4 (or ground) - this tells the EFI & SRS & ABS computers to go into diagnostic mode.
(you can also join pin1 to ground to make the computer flash the error codes)

Protocol / Packet Structure - Now the HARD part:
To this point the PC and CAR can send signals to each other using the hardware circuits listed above, but what are those signals to be?

It uses the hardware protocol ISO9141, but I have yet to work it out the exact packet structure and baud rate the Mitsubishi MUT / MUTII / MUTIII operates at.

links for similiar protocol packet structures: (subaru protocols working)

Let me know if you get the Mitsubishi protocol working, Thanks.
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