Signals on DLC connector, 1997 Jetta TDI

clyde

Veteran Member
Joined
Apr 8, 2000
Location
confluence, Snake/Clearwater
TDI
1998 Jetta, 1959 DeSoto with leopard-skin seat covers
In final stages of TDI conversion (1997 Jetta TDI 1Z engine into 1990 Jetta) I'm considering VAG-COM to get things set correctly.
So I checked the Bentley to see how the Data Link Connector is wired. That's where things got confusing.
According to the Bentley manual the 16-pin DLC connector is wired as follows:
pin 4 Brown ground
pin 5 Brown ground
pin 7 gray-white ABS, Motronic, airbag
pin 15 yellow transmission control module
pin 16 red-white +12 V
While I'm not an engineer, it seems quite strange that a computer program could diagnose what's going on with the electronic controls and the engine from +12V, ground, and airbag signals.
A first guess is that the schematic is a general diagram and that it is mislabeled, and that the pin 7 signal labeled "ABS, Motronic, airbag" (Motronic is an ECU used with a gas engine), actually is the signal from the diesel ECU used with the 1997 Jetta TDI.
If the pin 7 signal is the crucial signal line, it is probably wired appropriately for the TDI control unit.
This car has a manual transmission so its transmission control module is the driver, whose output signals are audio—not electrical via wire…
What I need to know is:
1. Whether I've been testing the right connector (it's black with purple on the exposed end—where another connector would plug in);
2. Whether a VAG-COM will work with only one active signal;
3. Any tests I can make to confirm that the DLC is wired right. It should be—it came from the factory this way; and
4. Anything else to help the newbie find his way out a corner.
Thanks!
 

Uwe

Vendor , w/Business number
Joined
Feb 24, 2000
Location
Lansdale, PA, USA
Yes, VAG-COM (or the factory scan tool) works with only one active signal on a car like yours, the K-Line on pin 7 of the diagnostic socket. Of course the interface also needs +12 (from pin 16) and Ground (from pin 4).

Check that you have +12 on pin 16 (test the voltage), a good ground on pin 4 (check resistance between there and the chassis, should be less than 1 ohm), and check continuity between pin 7 and the relevant pin on the harness connector for the ECU. That should be all you need for a scan-tool to talk to the ECU.

-Uwe-
 
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