Class 2 data bus? J1850?

**Rickertsen2** · 06-05-2005, 10:49 PM

I have a 2004 impala LS 1SC. Now everytime i go to do anyhting, look at a pinout for anything etc i find this mysterious thing called a "class 2 data bus" mentioned. Apparently it is a one wire asynchronous uniplex PWM modulated peer to peer serial bus(breathes). Various parts of the car use it to talk to each other and tell each other to do stuff. It contains vast amounts of useful functionality which i want access to. Almost ALL gm vehicles have one. I think that other vehicles have something similar. The problem is i can't find much info on it.

I have found some very basic info on the electrical nature of the bus, and how data is transmitted over it, but nothing on WHAT data is transmitted over it and how to do anything useful with it. Does anybody know anything about this bus? This could lead to some fun hardware projects.

Here is what i have found so far:
http://www.public.asu.edu/~pheanis/d...VBI_CLASS2.pdf
ftp://download.intel.com/design/inta...s/j1850_wp.pdf
http://www.gmtcny.com/serial%20data.html
http://www.fieros.de/en/Fiero2003/bridge.html

**Rickertsen2** · 07-05-2005, 04:20 AM

Cmon somebody must know somehting. I can't find ANYHTING. The only people who seem to know anything are GM and a few company's making factory integration gizmos etc and neither are talking. I am mainly concerned about info on the command structure for controlling things such as lights, locks, driver information center, message thingy, onstar, AC, and radio.

Example: look at the notice in red on the bottom of the page
http://www.pac-audio.com/protocol%20info/class2.htm

**Mechanic** · 07-05-2005, 12:53 PM

I believe you can find what you need here :

GM VPW Communications Protocol

**Rickertsen2** · 07-06-2005, 12:10 AM

Grr the link isn't working. Looks like they guy is using dyndns.org to forward to a server in Salt Lake City connected through comcast cable. Its prolly a server in his basement somewhere. In any case its not working

If anybody tries this page and it works could you please save it and forward it to me. Neither wayback nor google have that particular page archived.

**emf** · 07-06-2005, 01:47 AM

Some similar matches which appear to be on the air:
http://www.fastfieros.com/tech/vpw_c...n_protocol.htm
same info also at
http://www.hptuners.com/vpw.htm

Unfortunately, the archive and google cache have lots of pages, but nothing specific to the VPW protocol . . . so it's anyone's guess if all 3 links boil down to the same info.

**chewwtoy** · 07-15-2005, 02:55 PM

Class 2 is a proprietary proticol used by Ford and GM of J1850. In order for it to be useful you'll need to reverse engineer the signals using a hardware box. There are several on the market. The one I use is the neoVI (www.intrepidcs.com) because it supports so many protocols including j1850.

J1850 is the Lowlevel protocol for Class 2.

**chewwtoy** · 07-15-2005, 02:57 PM

Oh yeah.. and if your vehicle supports it you can always use j1978 or j1979 for standard diagnostics such as engine speed and VIN. This is the open standard set by the SAE to standardize information on in-vehicle networks.