VAGCOM Problems: New Issues and Solutions

Hello.

My attempts at data logging during test drives failed miserably today due to constant communication problems and a barrage of error messages, while all functions work perfectly fine with the engine idling.

Possible causes could be:
1. Vibrations from the running engine may cause loose connections to move.
2. Electrical system faults (e.g., voltage spikes from the alternator).
Batteries with voltages exceeding approximately 13 volts are causing problems.

The observation that isolated communication problems persist even after the engine is switched off (visible through the IC/TE/RE indicators and the fluctuating sampling rate of the measurement blocks), but disappear within a few minutes, suggests a voltage sensitivity in the communication system, which may originate from the adapter (since the battery voltage gradually decreases from approximately 14 to around 13 volts after the engine stops).

I understand that, under that assumption, it would be my responsibility to redesign the adapter accordingly.

However, I would like to ask beforehand if these symptoms are known and what you think the cause might be.

How is the K-line distributed within the vehicle's electrical system? During communication with the engine off, I always hear an irregular, faint ticking sound coming from deep within the dashboard, which could be something like a reed relay.
If the communication is happening through that system, and for example, its contacts are faulty, which component or control unit would need to be replaced or repaired?

What sampling rate do you achieve when displaying a group of values (usually four)?

With my auto-intern adapter, I achieved a measurement delay of approximately 0.38-0.45 seconds. However, this was without any fine-tuning; I didn't attempt to extract more data by increasing the data rate – it was essentially using the program's default settings.

When displaying three groups simultaneously, this value increased to 1.3...1.4 seconds.

What values are you getting approximately? If your sampling rate is significantly higher, that could be the cause, and your adapter might be innocent.

It ran stably, both when stationary and during operation, which had its fair share of jolts, and regardless of the engine speed (which, in my opinion, likely affects the CPU load of the control unit), as demonstrated by GarfieldMZs issues, where communication failed at higher engine speeds.

Best regards,

Jan.

Jan6K wrote:

What sampling rate do you achieve when displaying a group (usually four values)?

Hi Jan,

My standard display in the top left corner shows a value of 2.0 for group 1 (it fluctuates slightly when other groups are selected, but stabilizes again when the engine is stationary).

For groups of approximately 1.3, and for groups of approximately 0.7.

Quote:

What values are you getting, approximately? If your sampling rate is significantly higher, that could be the cause, and your adapter might be innocent.

Probably not, see above.

Quote:

It ran stably, both when stationary and during operation, which had its fair share of jolts, and regardless of the RPM (which, in my opinion, should affect the CPU load of the control unit), as GarfieldMZs' problems demonstrate, where communication failed at higher RPMs.

What still makes me suspicious:

Yesterday, I tried the same thing again, and everything went perfectly (or at least, I didn't notice any errors).
I did four data logging sessions with different injection starts, but I haven't figured out yet that the same filename is always used, so the old file is overwritten.
So, in the end, I only had the most uninformative file in the logs folder .

Today, after I finally figured out a quick way to preserve all the files (by renaming and moving them), my digital technology, my friend, of course, had something else in mind to mess with me...

Hi Ulf,

Sampling rate 2 closes at 0.5 seconds (I always calculate based on the timestamps in the log files, which is more accurate than the display, which I can't even see while driving), so it's very similar to mine.

I wasn't aware of the issue with the file names either. So far, I've only ever logged various things or had continuous logging running, which is more convenient than fiddling around with the computer (this is especially useful for the stress test; you can set these "markers" by precisely positioning the notebook's mouse pointer over them, and then just blindly press the mouse button while driving). However, this probably isn't a solution for you if you want to change values in the middle of the process.

Regarding the "splitting" of the control line, I'm afraid I can't help you with that either. However, I don't believe in relays that do that. My reasoning is that I've often read about aftermarket radios drawing the K-line to ground, which would disable the entire diagnostic system. This wouldn't be the case if they were individually selected. Therefore, I suspect a bus structure with appropriate addressing, so that everyone receives everything and can determine who it's intended for based on the address.

I still can't explain the relay ticking... are you sure it only happens during diagnosis and not also when you have the ignition on for a longer period? For example, the pre-glow might be reactivated if the engine hasn't started after a certain amount of time of glowing.

Are you taking the 12 volts directly from the car's battery for your circuit, or is there a stabilizer and smoothing circuit in between?

And finally... where does the device get its power? Did you choose this "Elite" model without a battery, or one with a battery? If both are connected to the car's ground (powered from the car's power outlet), there could still be some disruptive interference.

Here are a few thoughts on the issue...

Best regards,

Jan.

Hello Ulf,

Under certain circumstances, specific versions of files that are included with Internet Explorer can also cause connection interruptions. This is because, within the Microsoft DLL ecosystem, such issues are unfortunately possible.
I once experienced this issue on Windows 2000, using a colleague's laptop.
The same notebook worked perfectly fine under Win98 a few weeks prior.
You should be able to find something on Uwe Ross's homepage regarding this topic. It doesn't always have to be a problem with the hardware.

Best regards, Rainer.

Jan6K wrote:

Of course, I still can't explain the relay ticking... are you sure that he only experiences this during diagnosis and not also when the ignition is on for a longer time? For example, the pre-glow might be reactivated if the engine hasn't started after a certain amount of time of glowing...

Hi Jan,

Ticking is definitely related to communication. Without it, I can keep the ignition on for as long as I want - nothing happens.
While communicating via VAGCOM or a Pocket diagnostic tool, a ticking sound can be heard at variable rhythms, typically around 1 Hz. In some cases, it even occurs in sync with the K-line LED.

Quote:

Are you taking the 12 volts directly from the car for your circuit, or is there a stabilizer with smoothing circuitry in between?

A small smoothing capacitor, as shown in the diagrams on Rainer's website: 10 ohms and 100 µF, along with a 10 nF SMD capacitor.

Quote:

And finally... where does the device get its power? Did you get this elite group without a battery, or did you choose something with a battery? If both are connected to the car's ground (power supply from the onboard socket), there might still be something disruptive happening.

I have the Elitegroup model without a battery, powered by the included adapter. By the way, that adapter is a real voltage converter.
For example, it converts 11 volts at the input to 13 volts at the output and switches off completely at a voltage significantly below 11 volts (measured without load).

"In my opinion, voltage differences shouldn't really matter because the optocouplers provide galvanic isolation, which is, of course, 'offset' by the antistatic resistors..."

Rainer K. wrote:

Under certain circumstances, specific versions of files that are included with Internet Explorer can also cause connection interruptions. Because, in the M$ DLL hell, such things are possible. I once experienced this issue on Windows 2000, using a colleague's laptop. The same notebook worked perfectly fine with Windows 98 a few weeks prior. You should be able to find something on Uwe Ross's homepage regarding this topic. It doesn't always have to be a problem with the hardware.

Hi Rainer,

I'm generally already familiar with those software issues.

What makes me doubt that is:
Why does the communication work as soon as I turn off the engine?
(I can do this without the "ignition off" signal; I've installed a bypass button on pin 38 of the engine control unit / for the ALH and AHF models, it might be pin 47).
and the laptop continues to run with VAGCOM without any "disruptive intervention" from my side? Suddenly, the inputs that were just now acknowledged with hourglasses and error messages are executed flawlessly .

I have the Office 2000 package installed on my laptop running Windows 98SE, but I have everything disabled while VAGCOM is running.

Hi Ulf,

Rainer meant Windows 2000, not the Office suite, which is relatively harmless, and Windows 98 should also work fine.

Since it works perfectly fine when stationary, and only occurs during engine operation, I think the problem lies within the car itself, as the computer is largely unaffected.

What happens if you set the baud rate to half its value, meaning you sample less frequently?

Otherwise, it could be a fluctuation, but I'm not really sure about that. What does your pocket tester show when you connect it while the engine is running?

Best regards,

Jan.

Jan6K wrote:

Since it works perfectly fine when the engine is not running, and only occurs during operation, I think the problem is likely on the car's side, as the computer is essentially unaffected. What does your pocket tester do when you connect it while the engine is running?

Hello everyone.

I haven't yet specifically researched using a pocket tester while the engine is running - it can only read the memory, and for that, the engine doesn't need to be running.
I think I remember that it also works normally with the engine running - I think I saw a test done some time ago about disconnecting the EGR solenoid valve while the engine is running.


I just re-examined the approach of "excessive board voltage during motor operation" and replaced the R 6 resistor in the adapter from 2.2 kΩ to 3.3 kΩ.

After an initial quick test, everything now works even with the engine running.
However, under slightly different ambient conditions than yesterday: The engine and vehicle were cold to lukewarm, the outside temperatures were about 15°C lower, and the laptop was also cooler (yesterday, it took about 20 minutes before the trips to explore the data logging function --> saving instead of overwriting, etc.).

The on-board voltage is likely no longer a factor, as the charging voltage for the battery is adjusted to be slightly higher at lower temperatures, so we should have seen even more problems this morning.

Can general temperature differences, even those within the "normal" range, alone cause such error patterns?

I will observe the situation over the next few days and, if necessary, create another update for the adapter schematic.

ulf wrote:

...What makes me doubt that, however: Why does the communication work as soon as I turn off the engine? (I can do this without the "ignition off" signal; I've installed a bypass button on pin 38 of the engine control unit / for the ALH and AHF models, it might be pin 47). and the laptop continues to run with VAGCOM without any "disruptive intervention" from my side? Suddenly, the inputs that were just now acknowledged with hourglasses and error messages are executed flawlessly . I have the Office 2000 package installed on the laptop under W98SE, but I have disabled everything while VAGCOM is running.

Hello Ulf, here's how it manifested for me:
- constant clicking sound from the dashboard.
- When stationary with the engine off, there is a clicking sound, and connection drops occur occasionally.
- During test runs, there is always a failure at engine speeds above 3500 rpm .
I don't understand it, but it was like this .

Best regards, Rainer.

I don't understand it at all.

My equipment:
-toshiba tecra 540CDT
- DIY interface based on Jeff's interface (using optocouplers ILQ5, transistors BC546, and the rest according to the schematic), assembled on a breadboard and soldered with wire wrap ( http://www.ralfhandel.de/interface.jpg http://www.ralfhandel.de/interface-oben.jpg http://www.ralfhandel.de/interface-unten.jpg) ).
-1 meter shielded cable with open strands, connecting to the OBD connector.
-1.5m cable, 9-pin D-Sub, pre-wired.

In the initial logs, the laptop was running on battery power. From that point on, it was always connected to the power supply.
The last trip covered over 700 km to Austria and back (a total of 1400 km) in a Passat 1.8T, with a constant connection to VAG-COM.

The aging laptop (P233, 64MB, Win98) manages to process 1.7 log files per second in the engine control unit.

Other vehicles: A4 (year 1997), A4 (year 1999), Octavia (year 2002), Ibiza (year 1995, with L-line trim), Golf-II (year 1993, with L-line trim), Passat (year 2001).

No problem.

CU Gremlin.

btw: Rainer, your creations in the forum seem to be doing well .

Hello Ulf,

Perhaps the reason it's not working correctly while the machine is running is due to your potential equalization resistors.
Electrically, this creates a ground loop. When the motor is running, the ground potential can increase (due to the voltage drop on the ground wire) due to the connected devices. This leads to equalization currents flowing through the ground loop. Disturbances also readily couple into such loops. You can often hear this with ground loops in car radio amplifier connections. Your laptop will likely draw several amps through the power supply (which doesn't provide true galvanic isolation).
'Why don't you try running a test without a ground loop?'

Regards,

Eike.

PS: I will replicate the adapter as soon as it is running safely and stably at your place.

The November issue of the magazine Elektor also contains a circuit diagram.

Unfortunately, I do not have these http://www.elektor.de/ln/ln.htm.
I'm also interested in the article, maybe someone here has a subscription to that newspaper???

Aah, yes...


see also: http://www.elmelectronics.com/DSheets/ELM323DS.pdf


In simple terms: this device converts OBD data into ASCII format and functions similarly to a modem.

So, I forgot because it's not compatible with VAG-COM...

The circuit diagram is actually included in the datasheet, so 'don't worry about Elektor' .


CU Gremlin.

Rainer K. wrote:

In my case, it manifested itself as follows: - constant clicking sound from the dashboard. - When stationary with the engine off, there is a clicking sound, and connection drops occur occasionally. - During test runs, there is always a failure at engine speeds above 3500 rpm . I don't understand it, but it was like this

.

Hi Rainer,

was genau meinst Du mit "es" (im 1. Sure, here is the translation of the text from German to English:

"Sentence?"

Software incompatibilities? Or how else did you "solve" it?

Hello Ulf,

Yes, "it" was the Windows configuration that was behaving strangely.
I fixed the problem by buying a notebook myself.

http://www.ross-tech.com/vag-com/faq_2.html#Comm-None

Best regards, Rainer.