OBD2 To ECU connection issues

[semastang27]

Hey everyone!
First post here, loving everything I’ve read on the site so far hoping the community can help me out and looking forward to contributing in the future!

Got a strange issue with my 05 GT.

OBD2 has power and when a tuner (SCT) or scan tool is hooked up neither will link to the computer.

checked all of the fuses (both boxes) and all fuses have correct power and no blown fuses. Checked the cigarette lighter and that has power too.

there’s a couple of connectors unplugged under the dash **pics attached** and one plug I’m not sure of in the engine bay by the ecu **pic attached**

other than that a heads up this car is heavily modified (former SEMA car) with a built motor, -8 AN fuel feed line (fuel safe fuel cell), 6 speed trans, 9” Currie rear end, etc...

**the car has no ABS, evap, egr, no cats**

Really stumped here and hoping for some help or ideas on how to figure this issue out!

thanks!
-AJ

 

[Iceman62]

Sometimes alot of those unused plugs are N/A f/ your vehicle (common wiring harness used f/ all cars). First, have to ask, is your SCT new/unmarried?

 

[semastang27]

Yea definitely unmarried got it from a professional tuner and the regular obII (which works on my daily that’s a newer car) won’t connect either. It gets power but won’t link to the ecu...

 

[Juice]

The plug in the photo with the PS reservoir is C110 i believe. Part of the original engine harness. Cant see how that could be unplugged and have the car run.
You said it was a Sema car and a bunch of evap stuff deleted.
Based on that info, I suspect you have an aftermarket engine management system on that car.

 

[semastang27]

Are you talking about that 12 pin tan connector by the fuse box?

and yes evap deleted. Still running stock ecu and wiring harness. Trying to upload the tune but stuck with no connection from the obdII to ecu (gets power no connection)

 

[Juice]

Are you talking about that 12 pin tan connector by the fuse box?

and yes evap deleted. Still running stock ecu and wiring harness. Trying to upload the tune but stuck with no connection from the obdII to ecu (gets power no connection)

Yes, that 12 pin plug.
If you are sure you are running stock ecu, than the only thing left is the HS can wires are disconnected between the obd plug and pcm. There are 2 can wires + and - that the obd port connects to the pcm through.
On the obd connector, those are pins 6 & 14 IIRC. Not sure which pins on the pcm, but it will be in c175b connector.

 

[semastang27]

Ok, thanks for that! And are those two wires that black connector under the dash with the metal spring on it? I have a picture of it above

and what does that 12 pin connector go through? I’m looking at wiring diagrams but I’m really confused on where it goes.

thanks for your help man I really appreciate it!

 

[Juice]

Not sure how the can wires are routed. The pin locations I listed are at the connector where you plug in the x4 under the dash.
From what I remember on that 12 pin connector, it connects some of the engine harness circuits to the body harness.

I hate trying to trace modified wiring.

 

[semastang27]

Ok I’ll get in there and take a look!

and yea I agree with you. Luckily the modified harness was swapped out with this stock harness but it’s just a headache to figure this out.