K-line issue (just another one)

So after weeks (if not months) of occasional trial and error and not solving my issue I decided to try my luck here.. As the title suggests, this is (just another) K-line issue.

In summary: I have not been able to get any useful data from my ’99 Golf MKIV’s OBD-2 connection. I’ve spent hours browsing and reading into possible causes and have tried the solutions feasible with my limited resources. It seems that the K-line bus is fine, but my ECU doesn’t feel like responding.

Below is a list of the things I have already tried (and their results). In case I forgot some easy check/procedure, I’d be happy to find out. If not, the list might serve as a nice checklist for others with similar K-line issues.

• Started with a mobile ELM327 Wifi device, i.c.m. two different iPhone apps. OBD-II protocol error, or no connection to vehicle error. Connection to device seems fine, lights start blinking and all.
• Tested this device on a different VW Golf MK4 (petrol 2000) to rule out a faulty device, successful.
• Checked every compatibility list for OBD-2 I could find so far. If I’m correct my vehicle uses the ISO9141-2 protocol.
• Checked some fuses, amongst which fuse 12 for the OBD-2 connector and some ECU fuses. All good.
• Checked if the K-line was connected to my aftermarket radio. It is not. K-line is snipped and isolated.
• Nevertheless, unmounted the radio and tried again. No luck.
• Measured all pins on the OBD-2 connector:
  o 1-3 NC
  o 4 GND
  o 5 GND
  o 6 NC
  o 7 (K-line) 10V (which is inconclusive diagnose)
  o 8-15 NC
  o 16 12V
• Pulled, the K-line to GND using a 1kOhm resistor. Remaining voltage was c. 0.5V (if I recall correct), so no shortage to 12V (or GND).
• Started pulling fuses on K-line connected modules, amongst which ECU, ABS, Comfort system, instrument cluster, central locking and radio. After each fuse I did a retry. No luck. (BTW, airbag module has K-line but no fuse?)
• Got a 3rd party USB to OBD-2 cable. Downloaded VCDS Lite.
  o Can’t get past the test, because the interface is not found. (This is a common error in case the vehicle is unresponsive, so it seems)
  o Tried EasyOBD II to make sure my cable and interface are not faulty. It says the vehicle data bus is okay (validating my HW), but says no vehicle response. (See screenshot below)
  o (Want to try this on a different VW vehicle to ‘activate’ my VCDS Lite, but that’s currently not possible)
• Oh and before I forget, I did a ‘ECU reset’ as some call it by disconnecting the battery, putting ignition on, wait for 5 mins and restore. No luck.

Anything else I could try? Before driving off to the shop and try the real VAGCOM or start taking out modules like the ECU..

Are you able to connect to any other module? I mean you could try pulling the ECM connector off and measuring resistance on the K line from that connector to your OBD port. Is the car currently running? Why are you trying to connect with it?

I am unsure whether I can connect to the other modules. To my best knowledge, I would need the VCDS for that (which doesn't activate due to the failing initialisation test). Or is there another (free) software tool I can check that with?

I could undeed try to measure the K-line cable to check for faulty wiring. Haven't done that yet.
The car however, is running great. There is no direct urgent need to connect, however for the sake of hobby (and not being able to stand the fact that it doesn't work) I want to be able to connect and read out.

Fair enough. I'd check the continuity of the K line, see what you can get. Realistically you can connect to the K line anywhere in the system with VCDS and get a reading. Like if you take your OBD adapter with VCDS lite and tap into the K line you capped off at the radio it should work still. Just two options to start with.

pulling fuses on k line connected modules is not good enough, you need to physically unplug k connected modules one at a time until you isolate the problem... start with the door lock module driver side or take a peek inside the flex boot for broken/shorted wires

Nero Morg said:

Fair enough. I'd check the continuity of the K line, see what you can get. Realistically you can connect to the K line anywhere in the system with VCDS and get a reading. Like if you take your OBD adapter with VCDS lite and tap into the K line you capped off at the radio it should work still. Just two options to start with.

Click to expand...

Since the radio K-line was an easy one, I checked that first. Direct connection to the K-line on the OBD. So nothing new there.

For the ECM, I am starting to doubt whether it has a direct K-line connection. My Haynes manual has a page on the Diesel Injection Unit wiring (which I presume is ECM) with two gray/white wires of which one is at T121/16W. This wire only connects to the instrument cluster at T32a/5 apparently. The 'rest' of the K-line enters the instrument cluster at T32/25.
I am unsure whether there isn't another connection from the ECM directly to the K-line at this point. Otherwise this would mean that the instrument cluster could be the issue. Any thoughts here?

Nevertheless I ordered some play around wires and a female OBD-2 connector to be able to 'tap' the K-line and run diagnosis from there. May take a while since some things come from abroad

jimbote said:

pulling fuses on k line connected modules is not good enough, you need to physically unplug k connected modules one at a time until you isolate the problem... start with the door lock module driver side or take a peek inside the flex boot for broken/shorted wires

Click to expand...

I think I partially agree there. In case of a short you are absolutely right. But when a module is jamming the signal, wouldn't powering it off be sufficient?

Nevertheless I can give it a go. For the central door locking you refer to the CCM under the steering column (above the relais box) right?

Not always. When I did my manual swap I tried to just pull the fuse for the tcm, and it caused my ABS to go haywire. So I just disconnected the connector and all has been well since.

try a universal OBD2 scanner, such as a Launch CRP123, or what they use at the parts stores.
Just a regular, stand-alone OBD2 scanner. If that thing doesn't work, you got issue with the car.

If it does work, you probably have issues with the operating system on your computer.

I just bought a VagTacho 3.01 cable. And I was using on an older laptop, that was running Windows 10.
I didn't think anything about it, but spent about 6 hours trying every combination of variables I could think of. Hunting down ancient firmware files, trying 32-bit versions, 64-bit versions, etc. No matter what I did, the "interface is not found" would be the scenario.

I figured out that I should try the ol' reliable Windows XP. So I used a "virtual machine" emulator to boot XP inside of Windows10. I had that sucker working perfectly within 5 minutes.

As far as the ELM327 - I don't trust it. I used to own one of the bluetooth versions, and it was spotty, and only mildly helpful for checking basic OBD codes. That was about 3-4 years ago. I junked it when I figured out it doesn't "subscribe" to iPhone bluetooth protocols, so it will never connect, and the only way to use one is a wifi module like you specified. Still, I don't trust it much.
Mine (bluetooth, non-wifi) cost $7 on Amazon, and that's just about how much value I gained from it.

Although I'm a major amateur, I have strong feelings that the 1999 Golf ECUs are a different animal than even mine (a 2000) in terms of ISO protocols and K-line

Trying an auto parts store scanner (above) should rule out car problems.

By 'unmounted the radio and tried again' I assume you have an aftermarket radio.
Did you change the radio or did it come with the car?

There is an issue with this if the radio is not hooked up correctly.

Does your software work when used on other cars?

I all my enthusiasm I'm almost forgetting to thank everyone for his/her input. So here goes: Thank you!

2000alhVW said:

try a universal OBD2 scanner, such as a Launch CRP123, or what they use at the parts stores.
Just a regular, stand-alone OBD2 scanner. If that thing doesn't work, you got issue with the car.

[... a lot of stuff on compatibility, windows version and VWare ...]

Although I'm a major amateur, I have strong feelings that the 1999 Golf ECUs are a different animal than even mine (a 2000) in terms of ISO protocols and K-line

Click to expand...

Thanks, I knew I had forgotten something in my original list. My lil' brother works at a garage. Although they mostly do trucks and company vans, he tried to do a readout with a generic OBD-2 reader. No success. He recommended me to try find a VAGCOM somewhere. I have tried my ELM327 reader on other vehicles in the past. Successful! So yeah, I'm afraid the issue is with the car.

Regarding your comments on compatibility. I now know to re-install VMWare in case VCDS Lite also has trouble on other vehicles. I think I'll be able to try that (on a VW-vehicle) in two weeks or so. That application should be able to get much more info out than all the other generic readers, so will keep trying that.

wonneber said:

Trying an auto parts store scanner (above) should rule out car problems.

By 'unmounted the radio and tried again' I assume you have an aftermarket radio.
Did you change the radio or did it come with the car?

There is an issue with this if the radio is not hooked up correctly.

Does your software work when used on other cars?

Click to expand...

Radio is indeed aftermarket. Dealer put it in when I bought it as part of the deal. Haven't changed it since, but given that it's a crappy old thing I'm considering replacing it with one that does fancy bluetooth stuff.

As mentioned above the ELM327 has worked on other cars. Haven't been able to try the VCDS Lite on VW-car yet..

I haven't gotten my ELM327 to work with mine.
I use my original cable to my laptop.

So this morning I did some work again on the MK4 to figure out what's messing up the K-line. I disconnected the CCM, the driver side window motor/controller and the instrument panel (in various combinations). Unfortunately, still no luck. Same problem.

Next steps will be airbag and ABS. Is there anything else I'm forgetting to try disconnecting (besides ECM)?

I did find something else that I cannot wrap my head around.. I was under the impression that the CCM also controls central locking (no remote here). I was wrong, partially. With everything connected my central locking locks in a sort of a strange two step manner. First it locks the driver side lock together with another lock, when done, it locks two more locks, roughly 1 sec delay (not sure what locks which order). I always found that odd but didn't really bother. With the CCM disconnected, the central locking locked everything all at once. Apparently this is controlled from the window/controller. Very smooth. After reconnecting CCM, it went back to the old. What is up with that? After reading up on this, it seems that the two steps is 'normal' behaviour (and I was wrong about not all locks locking together, it's hard to tell..). Apparently first step is lock and second step is 'deadlock'..

Quick update on the above, for reference purposes.

I managed to do a read-out using VCDS-Lite. All my modules seem fine. Given that I now have the ability to read and clear fault codes I will no longer pursue a readout using general OBD-2. Also according to VCDS, the general OBD-2 readout is not supported on my vehicle, which is still confusing to me.