Hey I'm interested in hacking the com protocol on the C5 Vette.

I did this on my 1994 Z28 although that simply used a protocol similar to RS-232.

My preliminary research shows there are several variants on the OBD-II protocol. I'm not sure which one to research further as I don't know which one is for the corvette.

Does anybody know what the protocol is?

Where I could find additional information on the PCM?

Are there any forums devoted to this stuff etc.?

My goal is to create a cheap and simple adapter we could all use to interface with the PCM. It'll probably make use of a little microcontroller and would only cost a few dollars to build. The hard part is learning the protocol.

Thanks!

 

The J1850 bus is used for diagnostics and data sharing applications in vehicles. The J1850 bus takes two forms; A 41.6Kbps Pulse Width Modulated (PWM) two wire differential approach, or a 10.4Kbps Variable Pulse Width (VPW) single wire approach. The single wire approach may have a bus length up to 35 meters (with 32 nodes). A high resides between 4.25 volts and 20 volts, a low is any thing below 3.5 volts. High and low values are sent as bit symbols (not single bits). Symbols times are 64uS and 128uS for the single wire approach. The ISO 9141-2 single-wire asynchronous interface operates at 10.4kbps

Let me know when you get your prototype going!

 

Here's the data on the chip you're gonna need.

" The MC33390 is a serial link bus transceiver designed to provide bi-directional half-duplex communication meeting the automotive SAE Standard J-1850 Class B Data Communication Network Interface specification. It can be used at speeds up to 20 kb/s in non-standard applications.It is designed to interface directly to on-board vehicle microcontrollers and serves to transmit and receive data on a single wire bus at data rates of 10.4 kb/s using variable pulse width modulation. The MC33390 operates directly from a vehicles 12 V battery system and functions in a "true logic" fashion as an I/O interface shifting the micro- controllers 5.0 V CMOS logic level signals to 0 to 7.0 V waveshaped signal swings required of the bus. The bus output driver is short circuit current limited. A tristateable 4X/loop mode select pin is used to invoke normal wave shaped J-1850 Class B operation (0 V), disabled waveshaping high speed operation (5.0 V),or looped-back transmitted Tx output to Rx signal after having been wave shaped but not transmitted onto the bus (high impedance). The loop-back mode is used to confirm operational integrity independent of the bus. Though the MC33390 was designed for automotive SAE J-1850 Class B Standards, it is suited for other serial module-to-module communication applications.s was principally designed for automotive applications requiring SAE J–1850 Class B standards, it is suited for other serial communication applications.. It is parametrically specified over an ambient temperature range of – 40°C 3 T A 3 125°C and 7.0 V 3 V Bat 3 16 V supply. The economical 8–pin SO–8 surface mount plastic package makes the device a cost effective solution.he device a cost effective solution.. "

 

Just FYI,
In 2004, they went to a CAN network. Signaling is a little bit different.

 

Here's what I made:

http://sites.google.com/site/ehudv2/

It will work in any 1996-2003 Vette.

Here's what I'm working on for V1-HUD interfacing into the C5 and C6 (with additional complete OBD-II functionality for up to the 2003 model year).

http://sites.google.com/site/c6v1hud/

 

The 2004 C5 is different than the other C5s?