OBD2 help

[FFRWRX]

I've got a problem that I've spent many hours trying to sort out and have run out of things to check. So if anyone has a good understanding of the OBD2 connector, here goes.

I've got a 2006 Impreza WRX.

I've done a fairly extensive wire diet. The engine runs and everything seems to work; everything that I've hooked up and checked like all the lights, horn, instrument cluster. My scanner will hook up to the OBD2 connector on the harness and it gets power. It scans for a connection and then comes back showing there is an error and it can't connect (no particular error stated).

I've checked all the OBD2 connections and they all seem to be going where they are supposed to. There are only 5 wires (6 but 2 join into 1 right away). The connections from the connector to the scanner seem good and it worked fine before my wire diet. I left the battery disconnected for a while to see if that would help....it didn't. I am trying it with the key on as I always do.

Any suggestions? There are a number of connections to the OBD2 diagnostic connector to things like the clutch switch, the green test mode connectors, the neutral switch, that I can't really see being needed for the scanner to connect (but I do have them connected). What I'm after are the minimum connections to the OBD2 diagnostic connector just to get it to connect, without going through the other components. One connection goes to a bunch of harness braids...is that important to read codes?

The factory wiring diagrams are a bit strange when it come to this connector. If you look at the pages on "ground circuits" there is nothing for the WRX. The page for the Sti model has a ground for the 2 leads that go into one (I tried grounding that connection and it didn't help. If you go to "engine electrical system" there is one page showing the OBD2 connections and I've checked those.

So I seem to have eliminated anything you might suggest, but I'm asking anyways. And I assume that is the only way to read codes is with the OBD2 system working.

thanks,

Rick

[Ajzride]

I took my ECU out and hooked it up on the bench to help with troubleshooting. You can see some post on it here:

https://www.romraider.com/forum/viewtopic.php?f=15&t=16465

Here is what i hooked up on the bench ODB2 port (from amazon) and could talk:

12+ on pins 1,9
SSM (ECU Pin C16) on pin 10
12- on pins 12,13
Test Mode Detector (ECU pin B27) on pin 3

Keep in mind that Subaru labels the ODB2 pins backwards from most diagrams you will find online.

[FFRWRX]

Wow! Thank you very much for that. That's exactly what I was looking for, something with minimal hookups to see if the ECU, scanner, and my connections work. It worked before my wire diet. I'll try that later today and report back.

[FFRWRX]

Nope, no luck.

I have a very much jury-rigged setup, but I think I have it all hooked up correctly. Took me many tries since the wiring diagrams have the ECU connectors identified on the cables, not the ECU itself.....confusing.

131686

131687

One thing I did notice that I don't understand is that you have pin 3 on the data link connector going to the ECU pin27. In the car, there is nothing on pin 3 of the data connector:

131688

So I tried ECU pin27 going to pin 14 on my data link connector.....still didn't work.

To make sure I understand and have it correct, there is no other connection required to the ECU, only the 2 you have identified? Don't need to power it up? Or is it getting power somehow through the scanner when it is connected.

The ECU does run the car, so I assume it works. And I did run the codes several times before I did the wire diet. The scanner I'm using was working as well. Maybe I should see about borrowing a different one and trying that.

Edit: Just read the link you provided again. So is the ECU supposed to be powered up as well as the 2 connections you describe?

[Ajzride]

Yes, if you are pulling the ECU from the car there are a few power wires and a half dozen ground wires to hook up (that link spells out all of the power wires). My notes above were related to the OBD2 port only. And yes pin 3 was supposed to mean pin 14. Stupid Subaru labeling everything backwards.

[FFRWRX]

OK, getting there. Looks like I need power on A7, B2, and B19. And a whole bunch of grounds: D3, D7, D2, D1, C15, A5. Maybe don't need them all for testing, but no harm. I'll try it tomorrow.

thanks again

[Ajzride]

I think you need 12+ on B5 as well.

[FFRWRX]

Got it working! Man, what a pain that was to track down. I really appreciate the help Ajzride.

Hooked it all up on the bench and the scanner read the codes, so I knew the ECU and scanner were working:

131726

Put it back in the car and of course it didn't work. Checked the pins that should have 12v and the ones should be grounded. Then touched the 2 together and instantly melted my test leads. No, that was not on purpose, just not being careful enough. No harm done though (other than some test leads) not even a fuse blown. And the car still starts.

Then I checked the leads to the ECU and found one was not connected to the proper pin on the ECU. Pin C16 on the ECU is a light-green and black wire. So is the wire from pin C28. I had connected to that one thinking it was the correct wire. When I cut that off and joined it to pin C16 everything is good. I can read the codes now, so I can start to neaten up the wires and tuck them all away.

Then I checked what the wire to C28 does, and it connects to the Pressure Solenoid Valve which was deleted in the wire diet, so I had mistakenly connected the OBD2 connection to that wire that was cut off from the ECU bundle.

Sure am learning a lot about the wiring and the ECU.

Rick