J1850 Converter / Display 26.05.2007

Page updated 10.07.2007


I switched my old Chrysler Voyager to Jeep Renegade. Jeep is equipped with Programmable Communication Interface (PCI) bus (Chrysler terminology). Physical layer of this PCI bus is VPWM J1850 implementation. Vehicle control modules and Data Link Connector (DLC) are connected together with this bus. Of course my intention is to get my things listen and display the bus traffic.

I designed a small board for software experiments. This board can be used either stand alone display or J1850 to RS232 converter.


Board schematics

Board layout top

Board layout bottom

Populated PCB Picture

Test software for the board. Version 07.07.2007 See source code for details. Software is compiled with free (code size limited) version of CodeWarrior 4.6

Board finally put into a enclosure 10.07.2007 PCB mounted Ready picture

Test software includes OBD-II test display, some message decoding samples and PC data logging output.

Sample displays:

OBD-II decode

Transmission In/Out RPM & Status

Clock, odometer, fuel

Cruise control


First meaningful data was read from Jeep bus 26.05.2007. At my first piece of test code I have implemented few J1979 diagnostic protocol commands and their response interpretation. At LCD display we can look diagnostic responses in raw J1850 format or as scaled display. Converter also sends all bus traffic in ASCII HEX format to PC for later investigation. There are also some statistics available what is happening in the bus. Sample printout from short test drive.

Next step is to learn more about the protocols and start to hack Jeep private module to module messages.

10 09 B0 00 00 26 6C
92 21 00 13
1A 00 00 00 4B 81
B1 00 FA
10 09 BA 00 00 25 F0
35 01 08 F4
10 09 C9 00 00 25 B1

J1850 bus statistics
RX counter = 0046952
CRC errors = 00328
IFR messages = 02931
Inval symbol = 00000
Long RX msgs = 00000
TX counter = 00134
LOA counter = 00001
Drop frames = 00000
Time stamp = 0887954


I have done some desk work with drive logs.

List of decoded (hacked) messages 07.07.2007

If you have information or suggestions what yet unknown message may be please let me know. My email address


Main component data sheets

Freescale MC9S12DJ64 data sheet

Freescale MC33390 data sheet