2007 Impreza: tap into ECU to add check engine light

[torpedo51]

Hi,

I have a 2007 Impreza engine in my VW Syncro camper.  The ECU and engine harness are Subaru but the fuse panel, relay plate and dashboard are VW.  

For that reason, I don't have a check engine light on my dash.

I was wondering if there is a way to tap into the Subaru ECU so that I can run a wire up to my dash and illuminate a custom "check engine light".

 

[el_freddo]

Totally doable. You just need to find the ECU pinout (find a free online manual), find the CEL wire, run it to the dashboard and add power to the other side of the light. 

The info is out there, you just have to find it. I do t know of off hand otherwise I’d share it here with you. 

Cheers 

Bennie

[nvu]

Manuals are here https://sl-i.net/FORUM/showthread.php?18087-Subaru-Factory-Service-Manuals-(FSM)-Every-Model-USDM-EU

 

[torpedo51]

Thanks.  I'm trying to capture this at the ECM, because I don't have a harness for a Subaru dashboard.

Is it C11 on this diagram?  Thanks!

[nvu]

Looks like it, fairly sure the ecu sends a ground signal to turn on the light.  But to be safe, hook up a multimeter in volt mode, black lead to pin 11, red to 12v.  Check engine light is always on when motor isn't spinning and should go away when running.

[el_freddo]

That’s the wire you want. If it’s still in the plug (which it would be if just clipped!) it’ll be a red wire with a white trace line or pinstripe if you like. 

Definitely earth switched by the ECU, meaning put power to the other side of the check engine light and earth to the ECU. 

So it’ll just be a case of working out where to mount your light, pick up 12v ignition power from and run your wiring. 

Cheers 

Bennie

[torpedo51]

Sorry - I'm almost following this... which are you describing?  B?

A.  ECM pin >> + 12v signal >> [LED WARNING LIGHT] >> ground/earth
B.  + 12v (presumably an "ignition on" wire) >> [LED WARNING LIGHT] >> ECM pin >> ground/earth

Thanks!

Edited August 10 by torpedo51

[nvu]

B is right.  You could probably trace back where C7 leads to and run off that.  It's probably a good idea to figure out what C7 is and measure the voltage.  Come to think of it, I've not any experience with newer cars with led gauges.  I've been used to the 12v bulbs and assume they'd all be 12v.

C7 >> diode + >> diode - >> led + >> led - >> ECM

Put a real diode in between to protect the ecu.

[el_freddo]

B is what I meant, just without the earth after the ECU (unless this was just a reference to the ECU being earth switched) as listed in your description. 

Cheers 

Bennie

[torpedo51]

Got it, thanks.

Is there a trick to removing the wire from the plastic connector?  Even my smallest jewelers screwdrivers are too big for what I think is the release-hole.

I was hoping to splice and shrink-wrap, rather than to use a wire tap.

Thanks!

[torpedo51]

Ah - never mind.  I found a video explaining how to release the lock on the clip, and then a special (extra small) de-pin tool.

Splicing now.

Thanks!