I'm starting to wire my LS2 E36 swap. I have an E40 PCM (from a 2006 GTO, flashed to a 2006 SSR OS).

I have an Aeroforce scan gauge that I will be mounting in a console pod. Rather than fish the harness from the scan gauge to the factory OBD2 port location, I'd like to splice into the OBD2 port and extend the wires to the console to create a duplicate port specifically for the scan gauge, thereby leaving the original OBD2 port available for other purposes.

Is there any detriment in wiring things this way?

TIA.

 

 

Glad I asked. So of the six wires in the OBD2 port, it's just the serial feed that would create the issue? Have you even seen someone wire an application with the serial wire switched? I don't want to create a problem.

If need be, I'll hook the scan gauge to the factory OBD2 port. I was just hoping to keep the wiring a clean as possible.

 

yeah you can double em triple em etc. PeteS160 had me set my bench harness up this way so I could "spy" on what my reader is doing.

 

I'm getting a little confused. You're saying you disagree with what 8.lug wrote?

 

As far as I knew, OBD2 is point to point, not point to multipoint. Meaning you cannot Y the lines and have it communicate with 2 different things.

 

not exactly. i'm saying you can have as many ports as you want. like up to ten I think?

 

From what I have read u can several ports but only use one at a time. If u had obd port gauges u would have to turn them off or possibly unhook them to use a scan tool or other things but maybe I'm wrong. If u figure it out post up

 

It sounds like the debate is between how many you can HAVE at one time VS how many you can USE at one time. You can have many, but use only one at a time? That would make sense...

 

 

yeah thats my understanding. the computer can only converse with one thing at a time, but you can have multiple devices "listening" to the data on the bus.

pete could explain it better.

 

So you can hook various "passive" devices, but only one "active" that's actually "doing something".
Thanks Doug!

 

right. but its weird what is considered passive. like just running a speedo and a tach it's actually polling the computer X number of times per second...so that is actually an active communication.

 

https://en.wikipedia.org/wiki/CAN_bus (For the nickle tour)
Its a buss,, it can handle multiple devices connected and uses a protocol to handle who talks and who listens.

 

Well, that sorta blows it wide open! Multiple devices, and they get sorted out "in-house"! So to speak, anyway...

 

Okay...so for the layman; is the new consensus that my original plan is workable?

I'd just unplug the Aeroforce when necessary but the way I have it planned, the connection will be inaccessible without pulling the console apart.

 

yeah I think it'd work. we do that with my buddies car with an insight 2 dash thingy

 

The main trick. is looking though the wiring diagram and figuring out where you can pick up a connection, in theory you could tap the com wires behind the OBD connector and just add the plug of your choice somewhere else, like the glove box or whoever your new gadget will live, a regular RJ45 and unshielded twisted pair wire would work fine. Its designed to be a "dirty" bus, and at the speeds it communicates it takes a lot to tip it over as long as you keep the connections good quality. functionally you could picture it as two isolated studs and you could connect everything in the car to them and it would all talk.

 

My original plan was to cut the six wires leading into the OBD2 connector and splice each to add a second, remote OBD2 port for the AeroForce. I wanted this port to be placed behind the console, out of view.

If I remember correctly, the E36 OBD2 originally had 4 wires, and I had to add 2 for the E40 PCM. Below are pictures of the AeroForce harness. I bought the gauge used and unboxed. It's supposedly specifically for the '05-'06 GTO, from which my drop-out came (although I now have an '06 SSR OS on the E40). Interestingly, there are 8 pins in the AeroForce connector vs. 6 in the E40 OBD2.

I really don't want to create a problem. This swap has been dragging on for way too long and I need to get it going. Obviously, I don't have an in depth knowledge of the serial and CAN functions of the OBD2.

At this point, I think I should either simply plug the AeroForce into the existing OBD2. Or, if I do add a second OBD2 port, place it in an inconspicuous but accessible location, so I can unplug the AeroForce if need be, when plugged in to the original OBD2 for tuning, etc.

 

Your fine to splice the wires. just keep them tightly grouped and away from interference.

As for switching the signal...sure it can be but not with a switch it self. A switch is designed to open or close a circuit for electrical current to flow though. The serial data line is a transmission line not a power line, to prevent interference or skewed readings use an automotive 5 blade relay tol split the 2 DLC ports. signals. Singel from the car would come in on terminal 30 of the relay, DLC 1- terminal 2(Serial Data) would be on #87A of the relay and Dlc 2 - terminal 2(serial data) would be on 87. Now wire a switch up to the relay on terminals 85/86 and boom you have a switching data port. When the relay is off DLC 1 would have the active data line, when the relay was turned on DLC 2 would have the active data line.

If your wanting to switch a bunch of lines look on Amazon or Ebay for "Arduino Relay Module". It's relay boards designed to switch multiple relays with a single switch. You can get big one's....I picked up a couple of 16 relay boards for around 10 bucks each this past summer. So with 1 switch it controls 16 relays that are built into the module.

If your smart about what you use you don't need to switch any data lines. If you have 2 devices plugged in at the same time all that's going to happen is neither device will work correctly until you unplug one of them.

You can split GM class 2 on to at least 12 DLC ports if the cables are kept shorter and shielded well. 12 isn't a hard cap it's just the most times I've ever split a data line where I had tools connected to all the ports at once.

And to others in this thread just to make it clear there are 2 ways tools get data. By far the easiest and most common is by sending a pid request and reading the response. By sending the request you'd not intruding on the data bus...nothing wrong with that but it means you are directly interacting with the computer system. The second method is done passively and much....much harder to implement on Serial data just due to the limited about of data present. In a passive setup you only read data from the bus(no requests or commands are sent). On the later stuff right before the E38 switch over you can get things like Speed, Rpm, Temp, Oil pressure, Fuel level and stored codes but that's about it. On CAN stuff you can get pretty much anything you want from the data bus this way but it's VERY time consuming to map out every message and data byte.