Edit: It is a 2001 TT.
The car runs fine. I have tested power and ground on the OBD2 port. I tried disconnecting the ABS fuse. Tested the resistance through the power supply to the on board diagnostics and everything has checked out. Removed the ECU and inspected it externally and all looks good. Re tested wiggling wires at the ECU and at the obd2 port and got no result.
I am thinking that it is the ECU. Are there any other tests I can do or is it time to either send the ECU and or the whole car to the dealer for testing.
Dont want to swap out the ECU. This is a customers car and I want to make sure it is the ECU before we go there as they are pricy.
Have you checked continuity of the data wire from the obd-II port to the ECU?
I had a passat with a 1.8t that did that, the obd2 portitself was weird and would communicate if you wiggled it just right. Hope that helps.
In reply to Keith Tanner:
Working on figuaring out what pin out on the ecu is the data link. It looks like #30 but I am looking for conformation.
logdog
SuperDork
6/6/15 2:51 p.m.
More than just the ECU can pull the bus down. If any module has issues it can kill the network, or part of it. Are you using a scan tool that can check communication to things like the door or transmission modules? Is anything talking?
Yes I am using a bi directional scan tool. I have also taken the DOT emissions test equipment off line and tried. Neither can comunicate with the ECU.
Does anyone know the data pin out number on the ECU
logdog wrote:
More than just the ECU can pull the bus down. If any module has issues it can kill the network, or part of it. Are you using a scan tool that can check communication to things like the door or transmission modules? Is anything talking?
The thing is I dont think there is a can buss issue. I think it is an issue with the data port to the OBD2 conector from the ECU. I just need to verify continuity frm the obd2 port to the ECU. If that cheacks out it is almost certianly an issue in the ECU with the OBD2 data port.
The car runs fine and there are no lights on the dash saying there are any issues/codes.
In reply to dean1484:
Sounds like you just need to cut your losses and dump the car to someone in a location without inspections.
How much are you asking??? 
I can ask the customer but the REALLY like there car.
Does the customer know if the ECU has been reflashed or chipped?
+1 on asking for the tune/chip, some of those remove OBD functionality.
Also, are you using VAG-COM or a generic scan tool?
Using VAG-COM
The biggest test and the real necessity is getting the DOT emissions computer to talk to it. It knows it us plugged in to the car but can not communicate with the ecu to query it to get the emissions info.
No tuning or chipping of the car
And yes we know the DOT computer OBD2 is working. I inspected several other cars during the day while working on the TT.
