VAG cable does not work with engine running

[20VTGuy]

I have a 2001 GTI and I am using a generic VAG cable. Originally it worked fine. I can swear I was able to run the car with it plugged in and it pulled codes and such without issue. Now for some reason the only way I can pull codes is when the key is turned off. When the cable is plugged in and the car is running the software is unable to detect that its plugged in. The COM port settings are correct because as I said it works with the key off. I tried another generic cable with the same result. It used to work fine with the generic cable so not sure its to blame. Any idea why this is happening suddenly? The OBD port isn't the problem because it worked fine with the engine running for the cars recent NYS inspection.

[Dana @ Ross-Tech]

The only 2001 AWW Golf I had those issues with was hit by lightning and the ECM was bad. Before we go assuming the worst, run and save a complete Auto-Scan with the current VCDS-Lite release and post the results.

If possible, see if someone in your local area has a genuine VCDS system, like the KII-USB or HEX-USB+CAN, click Options -> Test and post those results with the communication outcome of the engine Key On and Running at idle.

[20VTGuy]

Thanks, I will try and run a Autoscan. I also just remembered I had a shop that works on Audi's and VW's pull codes and run some diagnostics about a month ago without a problem with the car running. I had them do it because all I am able to do with my cable is pull codes. I can't run any other diagnostic tests since it won't work for me with the engine on. So clearly it seems to be working normal except for me and my cables :-)

[20VTGuy]

I know this post of mine is old but I never followed up with it. I ran the autoscan but it won't complete. It only completes the engine module. Never gets through any other modues. And again it only works with the key off. And as I said originally this is with two different generic cables. As long as I keep the key off I can complete the engine module and read and clear the codes. Unable to do measuring blocks which is really what I want to do but the car has to be running for that and of course it won't work. Same error occurs. "No response from controller". Just seems odd that the ECM could be damaged since it will communicate with the the VAG with the ey off and it also read fine with the car running when it was hooked to our states inspection machine last year. What else could it be?

[Anony00GT]

A year later this still isn't resolved?

Have you gotten someone with a genuine interface to give it a shot, as suggested above?

[20VTGuy]

I just never followed up on it. The car was running fine and was getting through inspection so I just kinda put it by the wayside. Also it worked fine last fall with tester of a VW mechanic I use. He had a portable VAG and was diagnosing an idle problem and his VAG worked fine with the engine running. So the problem seems to be with my two cables and the VCDS Lite. When my first generic cable stopped working I assumed it was bad so I bought another generic but that didn't work either which is what lead me to post this originally. Guess I will try to track down a local guy with a Rosstech cable.

[Anony00GT]

Was your VW mechanic using a laptop or tablet with full VCDS on it? That may be your answer

[20VTGuy]

No, it definitely wasn't simply a laptop or tablet running Rosstech software. It was some sort of portable OBDII type machine about maybe 10"X6" and about 1.5" thick with the cable coming off it. It had a small LCD display and a series of membrane keys below. It was much larger than those handheld VAG scanners I see online. Didn't see it closely so not sure what make and model of product it was. He was running a series of tests with it, not just pulling codes, so I assume it was some sort of portable VAG.. He specializes in VW and Audi so I expect thats what it was.