OBD2 Wiring Help

[acolella76]

I started cutting up my S52 harness to swap into my '85. I started by repinning the harness to fit the early model square C101. Then I gained steam and basically started cutting shit. I cut the round diagnostic plug in order to use a generic OBD2 plug I can stick in the glovebox (to use Torque Pro or an Ultragauge). I just have a couple of questions about the wires that go to that plug.

There is a thick green and white wire that goes to pin #6 on this diagram (green and yellow on C101). On the E36 harness it goes straight to the diagnostic connector and nowhere else, can I get rid of this wire? Is this the 'signal' wire? I thought it was pin #17 (white/violet with yellow stripes)

I noticed there is a board in the cap of the diagnostic connector, and it looks like pin 16 (white/violet) and pin 20 (white/yellow) are connected via this board. Do I need to connect the wires or can I terminate them? Anything else I need to do with the other wires I cut?

Yeah I know I probably shouldn't have cut it but hindsight is 20/20. Any help would be appreciated.

[328ijunkie]

The diag port wiring is good to keep for a number of reasons. Without it and/or wiring mods you cant flash the ecu now through the harness.... The Grn/white is switched power for diag tools and the peake and whatnot.

[2mAn]

Did you have to modify the square c101 at all to re-pin it? I tried this on mine and the new BMW pins wouldnt fit into the opening of the c101, there was a "head" that was too large.

[acolella76]

I had these pins sitting around for 3+ years from the last time I did this. I'll see if I can dig up part numbers or something, but they went right in

[2mAn]

I wonder if they updated them. I just bought them earlier this year. The 3 larger ones in the middle of the C101 were fine, but the smaller ones (I think theres 4 or 5 wires) in the outer area wouldnt fit

[Sh3rpak!ng]

this is what I have on my diagram. I retained the round port under the hood and I've been meaning to wire up the obd2 port under the dash too (into the glove box so I can keep a wifi obd2 dongle plugged in)

You just reminded me I wanted to do this, so maybe it'll be my afternoon project



@Dave - is there another wire that can be tapped and pinned into the obd2 port to allow flashing the ECU from inside the car? (rather than using the round diag port under the hood?)

[Sh3rpak!ng]

I also have this. I pulled all the info straight from the ETM for e36 while I was obsessing over wiring my swap.

pins 2 and 17 are bridged in the cap of the round diag port

[328ijunkie]

Pin 18 on diag port needs +12 for ecu flash to 'take'

[Sh3rpak!ng]

Pin 18 on diag port needs +12 for ecu flash to 'take'

gotcha. so basically one could add a switch in the interior which would jump power to pin 18 on the diagnostic connector and allow you to flash the dme via the obd2 port under the dash somewhere from inside the car