# Another MK2 swap secret revealed..... VAG-COM and Check Engine How To



## smokinjoe644 (Nov 29, 2001)

Ok.... well I know this is something that was bothering me for some time now and probably alot of other people too. I have covered parts of this information elsewhere in my posts but I will try to make it all comprehensive here.
This will show you how to hook up the DLC (data link connection, aka VAG-COM) as well as a working check engine light.
The check engine light will work for any swap involving a CE2 fuse box and that originally had a CEL (check engine light). The DLC information is just for OBD2 swaps (VR6 and 2.0s) I will try to get some info for the OBD1 guys out there as well.
First up.... Check Engine Light
You will first need to find yourself one of the two styles of MK2 check engine lights that are out there. These are found either as a full sized dash switch (like the defrost and so on) or as an indicator in with the Ebrake and Seatbelt lights. Either one will work.
Next is the wiring, this is alot easier then you would expect, it is either 1 or 2 wires depending on the indicator you are using. The check engine light is triggered by a negative signal, just like the seatbelt and ebrake lights.
If you are using the standard in-dash switch you will need to run 2 wires. First is the easiest, you need to get a switched hot connection the the switch. This can easily be jumped off of the surround switches. I chose to use the hot from the defrost switch. This is a larger gauge black w/yellow wire. Splice into that wire and run a small piece off of it (about 6-8") put an insulated female spade connection on the end of it and connect to the back of the CEL switch on the post marked "15". The second wire is the trigger wire from the ECU. For this you will need to run a new wire down to your fuse box or over to your gauge cluster. You will need about a 4' piece and again another female spade connection. This will go on the "sl" pin of your switch. The third pin on the bottom is not used in this setup at all.
For the 3 in 1 warning light setup you will only need to run 1 wire. This is the same as where I left off above. This will connect from the CEL to the fuse box. You will have to drop down the fuse box and find the U1 plug. This is in the top row and is one of the two light blue plugs that run to the gauge cluster. Once you have located the plug find the wire at pin number 9. The plugs are marked on the sides. This should be a yellow w/red wire. This is your signal wire. Splice your new wiring into that wire and run it up to your CEL location.
***You can also find the signal wire at the following places, on the G1 plug at pin 9 (this is the actual wire to the ECU on the engine bay harness) or at the guage cluster***
I do not have a 3-1 warning light at this time so I cannot tell you the exact pin to connect the signal wire to... you can easily test with a meter or 12v power source to find which one lights up the correct bulb. (I will try to get one and post up the info)
That does it for the CEL.... now on to the VAG-COM
On OBD2 cars you will need to find a port with some wiring pig tailed to it. There will either be 4 or 5 wires coming off of the port depending on if you get it from a manual or automatic car (auto has one more). This is a 16 pin plug.
4 wire setup (manual trans)
Pins 4 and 5 go to ground (-)
Pin 16 goes to hot (+)
Pin 7 goes to the ECU source.
Pin 7 is your data source connect to the ECU to pull the codes. You will need to connect this to the ECU. The most direct way is to run a wire out to the ECU and splice into it near the brain box connection. If you use this method you will connect to the wire at pin 43 which should be a grey w/white wire. This wire does run into the car with the rest of the engine bay wiring as a single small pin connection which can also be located behind the fuse box. 
5 wire setup (auto)
same as above except pin 15 goes to the TCU
Pin 15 will be connected to the TCU at pin number 24 this should also be a grey w/white wire. This wire can also be located behind the fuse box.

OBD1 guys.... I am working on it... only have OBD2s at my disposal right now but I will put up more info as I get it.
I will put up some pics later to illustrate some of the wiring and plug locations. http://****************.com/smile/emthup.gif


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## vr6swap (Aug 17, 2001)

*Re: Another MK2 swap secret revealed..... VAG-COM and Check Engine How To (smokinjoe644)*

http://****************.com/smile/emthup.gif


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## shortshiften (Mar 29, 2005)

thanks dude\


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## VRsixty (Sep 29, 2003)

YES... Diag. port FTW!


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## WolfzGangVR6 (Jan 1, 2002)

*Re: (VRsixty)*

i was just about to start a thread about this... it's been bothering me for the longest time. a shop told me to find a obd1 port and wiring out of a 16v passat or gti/gli and run it to my fuse box. but that's about as detailed as they got. 
i have a pick'n'pull in my area that has plenty of 16v's and obd 1 harness's. just need to know how to wire it up http://****************.com/smile/emthup.gif 
hurry up and get that info for us obd1 swappers















one question though.. my original digi2 8v had the CEL in the cluster. not the switch type. will your diy work for me??


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## Boostin20v (Mar 22, 2000)

*Re: (WolfzGangVR6)*

great thread....I'd been too lazy to write something like this up for the swap FAQ in my sig....now when I get a chance I'm going to link to this thread http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif


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## smokinjoe644 (Nov 29, 2001)

*Re: (Boostin20v)*

I will try to have the rest of the info up early next week..... just wanted to put down what I had while it was fresh in my mind after finish up the project.
To simplify real quick.... wheather you are running an OBD1 or OBD2 swap you will still have the wiring you need to make this work. You can tap into both of the wires needed on the engine bay harness if you have different interior wiring.
There is simply one wire that comes into the car that is for the CEL, it is a negative signal that can either be constant or pulse. There is a second that comes in directly from the ECU to pull the codes. Everything else you can hook up to existing wiring since they are just power and ground connections no mater what wiring you have in your car (or run direct to fuse box) *once the wires (CEL and VAG connections) are in the car there are multiple places you can find them but you can always go back to the source to tap in if you need to


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## [email protected] (Jun 5, 2002)

*Re: Another MK2 swap secret revealed..... VAG-COM and Check Engine How To (smokinjoe644)*

Great info. The only thing I'd add is that the k-line isn't always on pin 43 of the ECU (check the wiring diagram for the donor car to know for sure) and some older vehicles have an L-line that needs to be hooked up in the same manner (again check the wiring diagram for the donor car to know for sure).








There's really no point in trying to wire up the separate black and white 2x2 connectors for pre-OBD-II since you'll just be using an adapter to convert them to 16-pin DLC anyway. http://****************.com/smile/emthup.gif


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## WolfzGangVR6 (Jan 1, 2002)

*Re: Another MK2 swap secret revealed..... VAG-COM and Check Engine How To ([email protected])*


_Quote, originally posted by *[email protected]* »_
There's really no point in trying to wire up the separate black and white 2x2 connectors for pre-OBD-II since you'll just be using an adapter to convert them to 16-pin DLC anyway. http://****************.com/smile/emthup.gif 

so instead of wiring the smaller connector, i would just run the L-line for my obd1 to slot 15 on a obd2 style connector?? 
thanks again andy and smokinjoe!! cheers


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## smokinjoe644 (Nov 29, 2001)

*Re: Another MK2 swap secret revealed..... VAG-COM and Check Engine How To (WolfzGangVR6)*

Ok... so as far as the Golf/Jetta swaps go for 2.0s and VR6s
Bentley shows all K-lines at Pin #43 at the ECU and as Grey/white on older OBD1s (93-94) the L-line is at Pin #21 and is Yellow
As posted above in the picture the K line goes to #7 on the DLC and the L line goes to #15
**Trying to get my hands on a Passat and Corrado Bentley to double check those locations** (anyone local to allentown that has them would be a great help)


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## WolfzGangVR6 (Jan 1, 2002)

*Re: Another MK2 swap secret revealed..... VAG-COM and Check Engine How To (smokinjoe644)*


_Quote, originally posted by *smokinjoe644* »_Ok... so as far as the Golf/Jetta swaps go for 2.0s and VR6s
Bentley shows all K-lines at Pin #43 at the ECU and as Grey/white *on older OBD1s (93-94) the L-line is at Pin #21 and is Yellow*
As posted above in the picture the K line goes to #7 on the DLC and the L line goes to #15
**Trying to get my hands on a Passat and Corrado Bentley to double check those locations** (anyone local to allentown that has them would be a great help)

what about a 95 obd1 vr6?? yes i pulled mine from a passat glx wagon. so would my L-line be yellow? 
sorry for constantly questioning, but i don't own a bently at the moment and don't have a way of finding the correct wire colors to splice. 
i picked up my obd2 connector and i'm in the process of looking for a dash switch check engine light cuz i think that's more mk2 style then in the cluster light.
again thanks a million. you just hooked up alot of swappers that didn't already have this info










_Modified by WolfzGangVR6 at 3:06 PM 8-21-2006_


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## smokinjoe644 (Nov 29, 2001)

*Re: Another MK2 swap secret revealed..... VAG-COM and Check Engine How To (WolfzGangVR6)*

Again, that info was for Golfs/Jettas.... as mentioned I do not have a passat bentley, I would guess it is also yellow but I cannot give you a 100% on that. 
Most 95s went to the 16 pin DLC not the 2 single connections according to the wiring diagrams I am working from, they still use the 2 wire setup, but in the newer plug.


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## WolfzGangVR6 (Jan 1, 2002)

*Re: Another MK2 swap secret revealed..... VAG-COM and Check Engine How To (smokinjoe644)*

perfect http://****************.com/smile/emthup.gif 
i should have it done by the weekend..
thanks again for all your help











































theres a sixer for you!
P.S. this is definitely one for the DIY section


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## splitmeister (Aug 9, 2001)

*Re: Another MK2 swap secret revealed..... VAG-COM and Check Engine How To (WolfzGangVR6)*

i def wouldnt go with the old DLC, unless youre goin for that old timey vintage status, as if you dont have your adapter, youre SOL scanning it.
Also, if you are doing a 1.8t and wire it into the old 2 plug DLC, for some reason revo SPS 3 will not work thru the 5051/3 adapter. weird, but it jus dun do it.


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## WolfzGangVR6 (Jan 1, 2002)

*Re: Another MK2 swap secret revealed..... VAG-COM and Check Engine How To (splitmeister)*

bringing back the dead.....
well i went to my local u-pull-it and grabbed a 16 port DLC connector out of a mk3 2.0 gl golf








i was looking at the chart up top and found that i have an extra ground in pin #5.. buth other then that all the wires are there... now to try and find the wires under dash


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## SuperChicken13 (Dec 6, 2003)

*Re: Another MK2 swap secret revealed..... VAG-COM and Check Engine How To (WolfzGangVR6)*

There's a DLC in here somewhere....
OBD2 ABA -> CE1 car. All you need is the DLC wire and a Ground / Track 15 source.


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## Pablo_san2 (Oct 3, 2008)

*Re: Another MK2 swap secret revealed..... VAG-COM and Check Engine How To (smokinjoe644)*

Any progress on an OBD1 go-around for this project?


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## bonesaw (Aug 8, 2004)

*Re: Another MK2 swap secret revealed..... VAG-COM and Check Engine How To (Pablo_san2)*

what go around? if its obd2 itll only have the grey/white wire. if obd1 you need the yellow wire also. power and ground. thats it.


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## theshanks (Sep 14, 2011)

Bringing back an old thread, sorry for that.

If one didn't have an OEM Check engine switch, as they are impossible to find, could you just use another 3 pole on off switch? I ask because there are several out there that directly fit into a Mk2 dash looking somewhat OEM and would probably do.

The car in question is neither OBD 1 or 2. Its an 8V Digi2 non California car. My understanding is that the wiring out of the ECM is still present tho.


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