Wiring in OBD on a Swap

h.ubk · Jan 31, 2017

Hi All,

I am starting to look into getting my OBD working on my 1997 Jetta Tdi again. Right now, I have power to the circuit, but no communication with the ECU. My car has a messed up electrical harness and possibly ancillary damage (see here for details -- http://forums.tdiclub.com/showthread.php?t=469276).

The car runs just fine. I just don't have OEM coolant temperature or VSS.

The goal is to drive it for a few years and then swap the engine into a Samurai or a Geo Tracker. For people who have swapped their engine into something else, could you enlighten me on what you did with the electrical wiring to make an OBD connection?

Thanks,

h.ubk

Alchemist · Feb 1, 2017

OBD II connections are pretty simple. All you need is power, ground, and K Line. The Pin 61 from ECU is based on an AHU, so you may have a different pin number, but the wire will be the same colour.

OBD Connector
4 Ground
5 Ground
7 K Line (Gray/White wire from ECU Pin 61)
16 Battery Power

h.ubk · Feb 1, 2017

Thanks, I just figured it would be a nightmare since there are so many pins on the connector. I suppose I could just relocate the port to under the hood if I don't want to trace the connector all the way...

h.ubk

frambach · Feb 2, 2017

On an ALH, the gray/white wire from the Data Link Connector (DLC) goes to the Instrument Cluster (IC). That's where the wiring schematic I'm using from ProDemand loses it.

There is also a gray/white wire coming from pin 16 of the ECM to the IC.

Using the same logic as for the AHU, do you think that if I ran the gray/white from pin 16 right to the DLC, I'd be good?

vtpsd · Feb 3, 2017

Alchemist nailed it. Very simple. Only those 3 wires. The k-line comes straight from the ecu.

pdq import repair · Feb 3, 2017

K line is where the communication happens. I have hooked up power and ground and k line only to ECU's on the bench and powered them up to talk to them independent of the car. Clusters too.

K line is the communication spider web so to speak. It does not go through any component, but rather to each component. The network of lines all communicate across it, and in theory if one component drops out the others wont be affected as they are all hooked in parallel to each other.

Shenandoah · Feb 3, 2017

Folks,

I took a look at the 2002 Golf wiring diagram from the Bentley and the Mitchell diagrams and see the following:

T121/16 (ECM grey/white) -> T10/1 (orange connector in plenum) -> T32a/5 (cluster green connector)

On the Bentley wiring diagram this has a 'W' next to the pin number on the ECM and the pin number on the cluster.

The K wire that goes to the 16 pin Data Link Connector comes from T32/25 (cluster blue connector).

Is the W wire (T121/16 ECM) the same as the K wire (T32/25 cluster)? OR does the cluster do something with the W wire from the ECM to make it the K wire?

Eric

oilcan_boyd · Feb 26, 2017

Shenandoah said:
Folks,

I took a look at the 2002 Golf wiring diagram from the Bentley and the Mitchell diagrams and see the following:

T121/16 (ECM grey/white) -> T10/1 (orange connector in plenum) -> T32a/5 (cluster green connector)

On the Bentley wiring diagram this has a 'W' next to the pin number on the ECM and the pin number on the cluster.

The K wire that goes to the 16 pin Data Link Connector comes from T32/25 (cluster blue connector).

Is the W wire (T121/16 ECM) the same as the K wire (T32/25 cluster)? OR does the cluster do something with the W wire from the ECM to make it the K wire?

Eric

I am in the middle of a ALH to Wrangler swap. The donor is a 2003 golf.
I can confirm the grey and white wire from PIN 16 does work when used for the OBD connector.

I don't know why the manual labels the wire "W" but when I connected that I was able to use Vag-com to see the ECM

h.ubk · Jun 9, 2017

So, I am thinking of moving the OBD port to under the hood just to make it easier when I eventually do my engine swap. I found a 1997 Jetta junkyard car (same car but gas) and pulled the OBD port. I also need Vagcom to time IP since I have a new timing belt.

Can I just take that OBD port and connect 4 and 5 to ground under the hood, 16 to battery power, and 7 to the grey/white pin 61 wire? Is there any possibility of damage if I just disconnect the battery, splice into the 61 wire and connect the OBD port from there?

Thanks,

h.ubk

h.ubk · Jun 9, 2017

It looks like I have an extra wire from the gasser 1997 Jetta I pulled the OBD port from. This is what I have:

4 and 5 = orange
7 = grey/white
15 = yellow
16 = red/white

What is the yellow wire?

h.ubk

vtpsd · Jun 12, 2017

who knows, but you dont need it if you want basic ECU comms. My AHU has power, ground and k-line. Works perfect.

BoostedOne · Jun 16, 2017

The yellow wire was another K line thats not needed for the ECU.. From what i remember, it is for the radio or something.
Also, its just me but I wouldnt go hacking up your harness further. The grey/white wire from the ECU goes to one of those colored junction boxes by the fuse box. then the OBD port wire plugs into that junction box.
Maybe one of the two just got unplugged from the junction box.

h.ubk · Jun 19, 2017

Thanks for the responses. Some of the wiring on this car is FUBAR (one reason it makes an excellent swap candidate). I was able to connect into pin 61 (gray/white) under the hood and wire up a junkyard OBD connector that let me communicate and check the timing. This really helps as it is one less thing I need to deal with when I pull the engine in the future.

h.ubk

Ric21 · Nov 16, 2022

Hi guys im running in a litle problem...i have a golf mk3 TDI 1z and i did a asv with a edc15vm+ swap car runs fine but if i start the car i cant comunicate with the ECU but if i only put the ingnition on (car not runing) i can enter the ECU like a normal car ... I have the k-line conected directly from odb to the ECU...Sorry about my poor English

Any ideas ? Thx for any help you guys can give me.

CasaEd · Nov 16, 2022

I would check your OBD plug connections. Check pin 16 in the obd plug is permanent live, engine off and running. Pin 4 in the OBD plug is earth, make sure that has a good connection, and also check pin 7 back to the ECU pin 16 with a multi-meter. Out of curiosity, is the K-line a direct line to the ECU, or are you connecting it to the original 1z connector block on the steering column ?

Ric21 · Nov 17, 2022

K line directly to the ECU ... I forgot to tell if i start the car and start coms with the ECU the car shuts down... If i only put the key on diagnostics works just fine ...Thx for your help

CasaEd · Nov 20, 2022

Never seen that problem before. How have you wired the ECU ? The same as the original ? Or seperate relay ? The car runs without vcds connected ?

Ric21 · Nov 21, 2022

Car runs fine without VCDs conected ... And VCDs works fine if i only put ing on... I connected obd directly to the batery and k line going directly to obd... And im getting 12v constante in the k line ( k line directly and only connected to odb)

CasaEd · Nov 21, 2022

You should not have 12v feed down the k-line, When you say OBD K-line wire direct you mean in the obd plug it's connected to pin 7 and in the 81pin
ECU plug it's connected to pin 16 ?

Ric21 · Nov 22, 2022

Ecu( edc15vm+) PIN 16 runing directly to obd PIN 7... so on the obd i have um PIN 16 with +12v directly from the bat PIN 4 with earth and PIN 7 going to PIN 16 on the ECU... Should i conect PIN 7 ( in obd )to PIN 81 on the ECU ? Thx for your help

CasaEd · Nov 22, 2022

Pin 81 of the ECU is for intake manifold air control solenoid, so no don't connect it there. If the car is running and you then plug into the obd plug the car stops ?

Ric21 · Nov 22, 2022

Let me try to explain ... You put ing on and you can see ECU dtcs real values etc if you start the car and try to do the same ( see dtcs ir real values) the car shuts down ...the car only shuts down when you start to communicate with ECU... You can leave the the obd plug with the car runing as long as you dont try to enter ECU ... Is like the ECU enters some safe mode and shuts down the car...

CasaEd · Nov 23, 2022

Do you have any fault codes in the ECU, and if so what are they ?

Wiring in OBD on a Swap

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